Category: Class 9

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 27 Hardware and Software Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 27 Hardware and Software

9th Science Guide Hardware and Software Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Find out the part which is not found in CPU?
(a) Mother Board
(b) SMPS
(c) RAM
(d) Mouse
Answer:
(d) Mouse

Question 2.
Which of the following is correct?
(a) Free and Open source
(b) Free and Traditional software
(c) Passive and Open source
(d) Passive and Traditional source
Answer:
(a) Free and Open source

Question 3.
LINUX is a
(a) Paid Software
(b) Licensed Software
(c) Free and Proprietary software
(d) Free and Open source software
Answer:
(d) Free and Open source software

Question 4.
Find out the Paid and Proprietary software from the given list
(a) Windows
(b) MAC OS
(c) Adobe photoshop
(d) All the above
Answer:
(d) All the above

Question 5.
……………… is an Operating system.
(a) Android
(b) Chrome
(c) Internet
(d) Pendrive
Answer:
(a) Android

II. Match the following :

MAC OS	Free and Open source Software
Software	Paid and Proprietary Software
Hardware	Input Device
Keyboard	RAM
LINUX	Geogebra

Answer:

MAC OS	Paid and Proprietary Software
Software	Geogebra
Hardware	RAM
Keyboard	Input Device
LINUX	Free and Open-source Software

III. Answer in brief:

Question 1.
What are Hardware and Software?
Answer:
Hardware is the parts of a computer which we can touch and feel. Hardware includes Input and Output devices, Cabinet, Hard Disk, Mother Board, SMPS, CPU, RAM, CD Drive, and Graphics Card.

Software is programmed and coded applications to process the input information. The software processes the data by converting the input information into coding or programmed language.

Question 2.
What do you mean by Operating System? How does it work?
Answer:
Operating System (System software): Operating system is software that makes the 1 hardware devices process the data fed by the user.
Working of Operating system: It works by displaying the results on the output devices ‘ like Monitor.

Question 3.
What is Free and Open Source Software? Give any two examples.
Answer:
Free and open software is available free of cost and can be shared with many end-users. Free software is editable and customizable by the user and this leads to the update or development of new software. Examples of Free and Open source software are LINUX, Open office, Geogebra, etc.

9th Science Guide Hardware and Software Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
The Software gives …………… in the monitor.
(a) input
(b) output
(c) a & b
(d) None of these
Answer:
(b) output

Question 2.
Word Processing Software is ………………
(a) Application Software
(b) System Software
(c) Hardware
(d) None of these
Answer:
(a) Application software

Question 3.
Windows is ……………..
(i) Application Software
(ii) Operating System
(iii) Free and Open-source Software
(iv) Paid and Proprietary Software
(a) i and ii
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer:
(d) (ii) and (iv)

Question 4.
Which one of the following is an Application Software?
(a) Mac
(b) Chrome
(c) Windows
(d) Android
Answer:
(b) Chrome

II. Fill in the blanks :

1. Graphic Card is a …………….
Answer:
Hardware

2. The Software processes the data by converting the input information into coding (or) programming ……………..
Answer:
Language

3. Free software is…………….. and …………….. by the user.
Answer:
editable, customizable

4. The application programmes can be installed in the …………….. for usage on a particular computer.
Answer:
Hard Disk

III. State whether true or false. If false, correct the statement:

1. The functions of Hardware and Software are separate.
Answer:
False.
Correct statement: The functions of Hardware and Software combine together.

2. We cannot see the functions of Software.
Answer:
False.
Correct statement: We can see the functions of the software in the form of output.

3. Application Software completes more than one work of the end-user.
Answer:
True.

4. The end users can legally use the pirated version of the paid and proprietary software.
Answer:
False.
Correct statement: The end users are legally prohibited to use the pirated versions of the paid and proprietary software.

IV. Assertion and Reason type questions : 

Mark the correct choice as :
(a) If both assertion and reason are hue and Reason is the correct explanation of Assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.

Question 1.
Assertion (A) : The functions of hardware and software combine together to make the computer functional.
Reason (R) : A computer is a device comprising both hardware and software.
Answer:
(a) Both assertion and reason are true and Reason is the correct explanation of Assertion

Question 2.
Assertion (A) : The free and open-source software cannot be updated (or) developed to new software.
Reason (R) : Free software is editable and customizable by the user.
Answer:
(d) Assertion is false but the reason is true
Assertion (A) : The free and open-source can be updated (or) developed to new software.

V. Answer very briefly :

Question 1.
How are parts of a computer compared to humans?
Answer:
A computer is like a human body, where the human body is the hardware and the soul is the Software.

Question 2.
What are the two forms of the operating system and application software?
Answer:
The Operating system and application software are available in two forms.
They are:

• Free and Open-source.
• Paid and Proprietary Software.

Question 3.
WhatisOSI?
Answer:
The Open Source Initiative (OSI), is an organization dedicated to promoting Open Source Software.

VI. Answer in detail :

Question 1.
What is Application software? How is it utilised?
Answer:
Application software is a program (or) a group of programs designed for the benefit of the end-user to work on a computer.

UTILISATION:

• The application programs can be installed on the hard disk for usage on a particular computer.
• This type of application program completes one or more than one works of the end-user.
  The following are examples of the application program:
  (e.g) Drawing tools, Editing software, Word Processing Software, Video player, Audio player, etc.

Question 2.
Write the conditions in the use of Paid and Proprietary Software.
Answer:
Conditions of Paid and Proprietary Software :

• The software needs a license to use it.
• We have to pay to use the software permanently (or) temporarily.
• The end-user is legally prohibited to steal the software program.
• The end-user is also prohibited to use the pirated versions of the software.
  (e.g.) Windows, Microsoft Office, Adobe Photoshop.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 22 World of Microbes Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 22 World of Microbes

9th Science Guide World of Microbes Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Which of the following is transmitted through air?
(a) Tuberculosis
(b) Meningitis
(c) Typhoid
(d) Cholera
Answer:
(a) Tuberculosis

Question 2.
One of the means of indirect transmission of a disease is
(a) sneezing
(b) coughing
(c) vectors
(d) droplet infection
Answer:
(c) vectors

Question 3.
Diptheria affects the
(a) lungs
(b) throat
(c) blood
(d) liver
Answer:
(b) Throat

Question 4.
The primary organ infected during tuberculosis is
(a) bone marrow
(b) intestine
(c) spleen
(d) lungs
Answer:
(d) lungs

Question 5.
Microbes that generally enter the body through nose are likely to affect
(a) gut
(b) lungs
(c) liver
(d) lymph nodes
Answer:
(b) lungs

Question 6.
The organ affected by jaundice is
(a) liver
(b) lungs
(c) kidney
(d) brain
Answer:
(a) liver

Question 7.
Poliomyelitis virus enters the body through
(a) skin
(b) mouth and nose
(c) ears
(d) eye
Answer:
(b) mouth and nose

II. Fill in the blanks:

1. …………….. break down organic matter and animal waste into ammonia.
Answer:
Decomposers

2. Typhoid fever is caused by ………………
Answer:
salmonella typhi

3. H1N1 virus causes……………..
Answer:
swine flu

4. …………….. is a vector of viral disease dengue.
Answer:
Aedes aegypti mosquito

5. …………….. vaccine gives considerable protection against tuberculosis.
Answer:
BCG

6. Cholera is caused by…………….. and malaria is caused by………………
Answer:
bacteria (Vibrio cholera), protozoa (plasmodium)

III. Expand the following:

1. ORS – Oral Rehydration Solution.
2. HIV – Human Immunodeficiency Virus.
3. DPT – Diphtheria Pertussis Tetanus.
4. WHO – World Health Organisation.
5. BCG – Bacillus Calmette Guerin.

IV. Pick out the odd one :

1. AIDS, Retrovirus, Lymphocytes, BCG, – BCG.
2. A bacterial disease, Rabies, Cholera, Common cold, and Influenza – Cholera.

V. State whether True or False. If false, correct the statement:

1. Rhizobium, associated with root nodules of leguminous plants fixes atmospheric nitrogen.
Answer:
True.

2. Non-infectious diseases remain confined to the person who develops the disease and do not spread to others.
Answer:
True.

3. The process of vaccination was developed by Jenner.
Answer:
True.

4. Hepatitis B is more dangerous than Hepatitis A.
Answer:
True.

VI. Match the following :

Swine flu	Human Papilloma vims Influeuza vims HINl
Genital warts	Human Immunodeficiency Vims
AIDS	Mycobacterium
Tuberculosis	Influenza vims HINl

Answer:

Swine flu	Influenza vims HINl
Genital warts	Human Papilloma vims
AIDS	Human Immunodeficiency Vims
Tuberculosis	Mycobacterium

VII. Define the following:

1. Pathogen
2. Bacteriophages
3. Vaccines
4. Prions
Answer:
1. Pathogen – A pathogen is a biological agent that causes disease due to its host E.g. Bacteria, Virus, etc.,
2. Bacteriophages – Virus that infect bacterial cells E.g. T4 bacteriophage.
3. Vaccines – Preparation of antigenic proteins of pathogens (weakened or killed) which on inoculation into a healthy person provides temporary / permanent immunity against a particular disease.
4. Prions – Prions are viral particles which contain only proteins. They do not contain nucleic acid.

VIII. Answer very briefly :

Question 1.
Distinguish between Virion and Viroid.
Answer:
Virion

1. Simple vims particle.
2. Grow and multiply in living cells.

Viriod

1. The protein-free pathogenic RNA of vims.
2. Found in plant cells and causes disease in plants.

Question 2.
Name the vector of the malarial parasite. Mention the species of malarial parasite which cause malignant and fatal malaria.
Answer:
The vector of the malarial parasite is the female Anopheles mosquito.
Malaria caused by Plasmodium falciparum is malignant and fatal.

Question 3.
What is triple antigen? Mention the disease which can be prevented by using the antigen.
Answer:
Triple antigen : It is combination of three vaccines (DPT).
Preventable diseases : Diptheria, Pertussis (Whooping cough) and Tetanus.

Question 4.
Name the chronic diseases associated with respiratory system.
Answer:
Chronic diseases associated with the respiratory system are; Diptheria, Whooping Cough, Tuberculosis.

Question 5.
Name the organism causing diarrhoeal disease and give one precaution against it.
Answer:

1. Rotavirus.
2. Precaution : Proper sanitation and hygiene.

Question 6.
Name two common mosquitoes and the diseases they transmit.
Answer:
Anopheles mosquito and Aedes aegypti mosquito are common mosquitoes that transmit malaria, Chikungunya and Dengue.

IX. Answer briefly :

Question 1.
Give an account of classification, of bacteria based on the shape.
Answer:
Bacteria are microscopic, single-celled prokaryotic organisms without a nucleus and other cell organelles. Although the majority of bacterial species exist as single-celled forms, some appear to be filaments of loosely joined cells. The size varies from less than 1 to 10 µm in length and 0.2 to 1 µm micrometer in width.
Based on the shapes, bacteria are grouped as:

1. Spherical shaped bacteria called cocci (or coccus for a single cell).
2. Rod-shaped bacteria called bacilli (or bacillus for a single cell).
3. Spiral shaped bacteria called spirilla (or spirillum for single cell)

Question 2.
Describe the role of microbes in agriculture and industries.
Answer:
Microbes in Agriculture :
Microbes play an important role in agricultrue as biocontrol agents and biofertilizers.
(i) Biocontrol agents :
Microorganisms used for controlling harmful or pathogenic organisms and pests of plants are called as biocontrol agents Biopesticides.
(E.g) Bacillus Thuringiensis.(Bt) is a species of bacteria that produces a protein called as ‘cry’ protein.

(ii) Biofertilizers:

• Microorganisms which enrich the soil with nutrients are called as biofertilizers.
• Bacteria, cyanobacteria and fungi are the main sources of biofertilizers .
• Atomspheric nitrogen has to be converted to available form of nitrogen.
  Example: Azotobacter, Nostoc (free living), Symbiotic microbes like Rhizobium, Frankia.

Microbes in Industries
Microorganisms play an important role in the production of wide variety of valuable products for the welfare of human beings.

Production of fermented beverages: Beverages like wine are produced by fermentation of grape fruits by Saccharomyces cerevisiae.

Curing of coffee beans, tea leaves and tobacco leaves : Beans of coffee and cocoa, leaves of tea and tobacco are fermented by the bacteria Bacillus megaterium. This gives the special aroma.

Production of curd : Lactobacillus sp. converts milk to curd.

Production of organic acids, enzymes and vitamins : Oxalic acid, acetic acid and citric acid are produced by fungus Aspergillus niger. Enzymes like lipases, invertase, proteases, and glucose oxidase are derived from microbes. Yeasts are rich source of vitamin-B complex.

Question 3.
Explain the various types of viruses with examples.
Answer:
Viruses are categorised as :
1. Plant virus : Virus that infect plants.
E.g. Tobacco mosaic vims, Potato vims, Cauliflower mosaic virus.

2. Animal virus : Vims that infect animals.
E.g. Adenovims, Retrovims (HIV), Influenza vims, Polio vims.

3. Bacteriophages : Vims that infect bacterial cells.
E.g.T4 bacteriophage.

Question 4.
Suggest the immunization schedule for a new born baby till 12 months of age. Why it is necessary to follow the schedule?
Answer:
The immunization schedule must be followed so that the vaccines administered will protect the children in the future from infectious and life-threatening diseases.

Immunization Schedule for Children

X. Assertion and Reason :

Mark the correct statement as:
(a) If both A and R are true and R is correct explanation of A.
(b) If both A and R are true but R is not the correct explanation of A.
(c) If A is true but R is false.
(d) If both A and R are false.

Question 1.
Assertion : Chicken pox is a disease indicated by scars and marks in the body.
Reason : Chicken pox cenlses rashes on face and further spreads throughout the body.
Answer:
(a) Both A and R are true and R is correct explanation of A

Question 2.
Assertion: Dengue can be treated by intake of antibiotics.
Reason : Antibiotics blocks the multiplication of viruses.
Answer:
(d) Both A and R are false

XI. Higher Order Thinking Skills :

Question 1.
Suggest precautionary measures you can take in your school to reduce the incidence of infectious disease.
Answer:

• Clean and hygienic environment should be maintained inside and outside the school.
• Enough first aid medicines should be kept in the school.
• Proper awareness about healthy diet and health instructions should be instructed to the students.
• If a student is identified with disease, it must be properly communicated to the students and nearby health authorities.
• The infected student / person must be kept away from other students in order to avoid the spread of infection.

Question 2.
Tejas suffered from typhoid while, Sachin suffered from tuberculosis. Which disease could have caused more damage and why?
Answer:
Tuberculosis is more dangerous than typhoid.
Reason : Tuberculosis (TB) primarily affects lungs and also affect intestines, bones, and joints and other tissues of body. Severe cases may lead to death.

Intext Activities

ACTIVITY – 1

Take the root nodules of any pulse or leguminous plant available in your locality. Wash it thoroughly with water. Crush the nodules on a clean glass slide. Add a drop of distilled water to the crushed material on the glass slide. Observe the preparation under compound microscope.

Observation of Symbiotic microbes.

Aim : To observe symbiotic bacteria shape on a clean glass plate.

Materials Required :
1. Root nodules of leguminous plant, Clean glass slides, Water, Distilled water.

Procedure :

1. Take the root nodules of the leguminous plant.
2. Wash it thoroughly with water.
3. Crush the nodules on a clean glass slide.
4. Add a drop of distilled water to the crushed material on the glass slide.

Observation:

Conclusion :
The structure of symbiotic bacteria is observed in a clean glass plate.
[End of the activity]

ACTIVITY – 2

Observe the mosquitoes that are active during the day time. Catch them using an insect net and observe their body and legs. What do you observe? Why are cases of Dengue reported in large numbers during post-monsoon season?

Observation :
Body and legs of Aedes aegypti :
We can find black and white stripes on the bodies and leg.
The white marking in the leg is in the form of a lyre.

High Dengue cases during post-monsoon

1. Due to the rainy season, conditions like stagnant water favours the mosquitoes to grow in large number.
2. Thus, a sharp rise in dengue cases are reported. [End of the activity]

9th Science Guide World of Microbes Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Which one of the following is a symbiotic bacteria?
(a) Azospirillum
(b) Azotobacter
(c) Rhizobium
(d) None of these
Answer:
(c) Rhizobium

Question 2.
The shape of Vibrio cholerae is
(a) Spherical
(b) Spiral
(c) Rod
(d) None of these
Answer:
(b) Spiral

Question 3.
……………are the site of protein synthesis in bacteria.
(a) Ribosomes
(b) Chromosomes
(c) Plasmid
(d) Nucleus
Answer:
(a) Ribosomes

Question 4.
Fungi reproduce through …………..
(a) binary fission
(b) budding
(c) spore formation
(d) all of these
Answer:
(d) all of these

Question 5.
Which one of the following is not an antibiotic derived from Bacteria?
(a) Cephalosporin
(b) Erythromycin
(c) Bacitracin
(d) Streptomycin
Answer:
(a) Cephalosporin

Question 6.
AIDS is’ a …………… disease.
(a) Endemic
(b) Epidermic
(c) Pandemic
(d) Sporadic
Answer:
(c) Pandemic

Question 7.
Fever, sore throat, and choking of air passage are symptoms of ……………
(a) influenza
(b) diphtheria
(c) whooping cough
(d) typhoid
Answer:
(a) influenza

Question 8.
Myxovirus is the causative agent for …………… disease.
(a) common cold
(b) measles
(c) influenza
(d) diarrhoea
Answer:
(c) influenza

Question 9.
The symptoms of measles is ……………
(a) eruption of small rashes in skin
(b) redness of eye
(c) pneumonia
(d) all the above
Answer:
(d) all the above

Question 10.
The stages of malarial parasite are developed in the …………… of mosquito
(a) respiratory tract
(b) gastrointestinal tract
(c) intestinal tract
(d) none of these
Answer:
(b) gastrointestinal tract

Question 11.
Incubation period of the virus for chikungunya is usually . ……………
(a) 2-12 days
(b) 2-7 days
(c) 4-8 days
(d) 3-9 days
Answer:
(a) 2-12 days

Question 12.
The disease that displays Nocturnal periodicity ……………
(a) swine flu
(b) dengue
(c) filaria
(d) influenza
Answer:
(c) filaria

Question 13.
Nasal spray vaccine can be administered to ……………patients.
(a) chikungunya
(b) dengue
(c) influenza
(d) swine flu
Answer:
(d) swine flu

Question 14.
Human Immuno deficiency Virus (HIV) was first isolated by …………..
(a) Robert Koch
(b) Robert Gallo
(c) Ronald Ross
(d) Louis Pasteur
Answer:
(b) Robert Gallo

Question 15.
The disease that is eliminated totally by the vaccination process is …………….
(a) chicken pox
(b) Filaria
(c) smallpox
(d) None of these
Answer:
(c) small pox

Question 16.
Among the following, which is belongs to water-borne diseases?
(a) Hepatitis A
(b) Hepatitis B
(c) Influenza
(d) Dengue
Answer:
(a) Hepatitis A

Question 17.
Measles vaccine can be administered to the child at the age of ……………
(a) 18-24 months
(b) 15-18 months
(c) 9-12 months
(d) 14th week
Answer:
(c) 9 – 12 months

Question 18.
Mycology is the branch of biology that deals with the study of ……………
(a) algae
(b) virus
(c) bacteria
(d) fungi
Answer:
(d) fungi

Question 19.
The major constituent of vinegar is ……………
(a) citric acid
(b) acetic acid
(c) oxalic acid
(d) hydrochloric acid
Answer:
(b) acetic acid

Question 20.
Bacteria involved in curd formation is ……………
(a) Lactobacillus acidophilus
(b) Nitrosomonas
(c) Bacillus ramous
(d) none of the above
Answer:
(a) Lactobacillus acidophilus

Question 21.
The most fetal form of malaria is caused by ……………..
(a) Plasmodium ovale
(b) Plasmodium falciparum
(c) Plasmodium malariae
(d) Plasmodium vivax
Answer:
(b) Plasmodium falciparum

Question 22.
Syphilis is caused by ………………….
(a) Treponema pallidum
(b) Leptospira
(c) Pasteurella
(d) Vibrio cholerae
Answer:
(a) Treponema pallidum

Question 23.
Mosquito-borne viral diseases are …………………
(a) malaria and yellow fever
(b) dengue and chikungunya
(c) filariasis and typhus
(d) kala-azar and diphtheria
Answer:
(b) dengue and chikungunya

Question 24.
Which one of the following is a pair of viral disease?
(a) Filariasis, AIDS
(b) Common cold, AIDS
(c) Dysentery, Common cold
(d) Typhoid, Tuberculosis
Answer:
(b) Common cold, AIDS

Question 25.
Which of the following disease is spread by animal bite?
(a) Pneumonia
(b) Tuberculosis
(c) Cholera
(d) Rabies
Answer:
(d) Rabies

II. Fill in the blanks :

1. Bacterial cell was covered by a strong cell wall made up of ……………
Answer:
peptidoglycan

2. In bacteria, a small extra chromosomal circular DNA called ………….. is found in the cytoplasm.
Answer:
plasmid

3. ………………bacteria live on dead organic matter.
Answer:
Saprophytic

4. Viruses are non-cellular, …………………… parasites.
Answer:
self-replicating

5. Adenovirus is………………….virus.
Answer:
animal

6. The cell wall of fungi is made up of ……………… and …………….
Answer:
cellulose, hemicellulose

7. Prions do not contain …………………..
Answer:
Nucleic acid

8. ‘Cry’ protein is produced by the bacteria………………….
Answer:
Bacillus Thuringiensis

9. Yeasts are rich source of …………………..
Answer:
vitamin – B complex

10. Vaccines stimulate the body to produce …………………. against the …………………. in the microbes.
Answer:
antibodies, antigen

11. Cholera is a ………… disease
Answer:

12. The interval between infection and first appearance of the diseases is called …………………..period.
Answer:
incubation

13. …………. is the Father of Bacteriology
Answer:
Robert Koch

14. The causative agent (bacteria) of whooping cough is ………….
Answer:
Bordetalla pertussis

15. Inflammation of nasal mucosa and pharynx are the symptoms of ………….
Answer:
influenza

16. The most vulnerable age of polio is between ………… years
Answer:
3 – 6

17. Use of ………… drugs kills the stages of malaria parasite.
Answer:
Quinine

18. Dengue is known as ………… fever.
Answer:
Break bone

19. Nilavembu kudineer is known to increase…………
Answer:
blood platelet count

20. The process of vaccination was introduced by ……………….
Answer:
Edward Jenner

21. The hyphae with branches form a complex network called ……………
Answer:
mycelium

22. First antibiotic …………… was developed by ……………
Answer:
penicillin, Alexander Fleming

23. Baker’s yeast is …………….
Answer:
the yeast used in baking bread

24. The two non-symbiotic nitrogen fixing bacteria are ……………and ……………
Answer:
cyanobacteria, Azotobacter

III. Match the following :

I.

1. World Anti-Tuberculosis day	a) 7th April
2. World Malaria day	b) 1st December
3. World Health day	c) 24th March
4. World AIDS day	d) 25th April

Answer:
1 – c, 2 – d, 3 – a, 4 – b II.

II.

1. Rhizobium	a) Phosphorus
2. Azotobacter	b) Soil bacterium
3. Mycorrhizae	c) Anabaena
4. Azolla	d) Antifungal compounds

Answer:
1 – b, 2 – d, 3 – a, 4 – c

III.

1. Saccharomyces cerevisiae	a) Biofertilizers
2. Mycorrhizae	b) Organic acids
3. Aspergillus Niger	c) Fermented beverages
4. Bacillus Megaterium	d) Curing of tobacco leaves

Answer:
1 – c, 2 – a, 3 – b, 4- d

IV.

Diseases	Incubation Period
1. Dengue	a) 2-12 days
2. Chikungunya	b) 5-6 days
3. Filaria	c) 4 2-7 days
4. Avian Influenza	d) 8-16 months

Answer:
1 – b, 2 – a, 3 – d, 4- c

V.

Answer:

IV. State whether True or False. If false write the correct statement

1. Virions are the smallest among the infective agents.
Answer:
True.

2. Viruses are devoid of cellular organelles like ribosomes^ mitochondria, etc.
Answer:
True.

3. Prions are found in neurons and are cone-shaped.
Answer:
False.
Correct statement: Prions are found in neurons and are rod-shaped.

4. In human beings, antibodies are used to cure infectious diseases like cholera, typhoid, etc.
Answer:
False.
Correct statement: In human beings, antibodies are used to control infectious diseases like cholera, typhoid, etc.

5. An infection develops when these pathogens enter the human body.
Answer:
True.

6. Airborne diseases are caused by fungi.
Answer:
False.
Correct statement: Airborne diseases are caused by bacteria and viruses.

7. Influenza commonly occurs during adult age.
Answer:
False.
Correct statement: Influenza commonly occurs during childhood.

8. Malaria is caused by the fungal parasite plasmodium.
Answer:
False.
Correct statement: Malaria is caused by the protozoan parasite Plasmodium.

9. Filaria is transmitted by the bite of an infected Culex mosquito.
Answer:
True.

10. Swine flu spreads through the air by an acute respiratory virus.
Answer:
True.

11. Hepatitis A causes cirrhosis of the liver.
Answer:
False.
Correct statement: Hepatitis B causes cirrhosis of the liver.

12. Oral polio vaccine is a killed vaccine.
Answer:
False
Correct statement: Oral polio vaccine is a Live vaccine.

13. Glycogen and oil globules are stored forms of food in fungi.
Answer:
True.

14. One of the differences between virus and viroid is the presence of protein coat in viroid and its absence in the virus.
Answer:
False.
Correct statement: One of the differences between virus and viroid is the presence of protein coat in vim:: and its absence in viroid.

V. Assertion and Reason :

Mark the correct answer :
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but the reason is not the correct explanation of assertion.
(c) If Assertion is true but Reason is false.
(d) If Assertion is false but Reason is true.

Question 1.
Assertion: Some bacteria may be non-motile.
Reason: Bacteria have a special structure called flagella which are found on cell surfaces.
Answer:
(d) Assertion is false but Reason is true

Question 2.
Assertion : Bacillus Thuringiensis is a biocontrol agent.
Reason : It produces a protein called ‘cry protein’ which kills insect larva.
Answer:
(a) Both assertion and reason are true and Reason is the correct explanation of Assertion

Question 3.
Assertion : Cancer is a non-infectious disease.
Reason : Cancer is caused by external factors like pathogens invading the body.
Answer:
(c) Assertion is true but Reason is false
Reason : Cancer is caused by internal factors like the malfunctioning of organs.

Question 4.
Assertion : An infection develops when pathogens enter the human body.
Pathogen enters the human body through contaminated air, water, food, soil, physical contact etc.
Answer:
(a) Both assertion and reason are true and Reason is the correct explanation of Assertion

Question 5.
Assertion : Chikungunya is transmitted in humans by the bite of infected Aedes aegypti mosquito during the day time.
Reason : Chikungunya is caused by Rotavirus.
Answer:
(c) Assertion is true but Reason is false]
Reason : Chikungunya is caused by a single-stranded RNA virus.

VI. Expand the following :

1. CJD
2. TT
3. OPV
4. HAY
5. AIDS
6. MMR

Answer:

1. CJD – Creutzfeldt -Jakob Disease
2. TT – Tetanus Toxoid
3. OPV – Oral Polio Vaccine
4. HAV – Hepatitis A Virus
5. AIDS – Acquired Immuno Deficiency Syndrome
6. MMR – Mumps, Measles, Rubella

VII. Define the following :

1. Disease, 2. Infection, 3. Antibiotics, 4. Toxin, 5. Vector
Answer:
1. Disease:
The disease can be defined as an impairment or malfunctioning of the normal state of the living organism that disturbs or modifies the performance of vital functions of the body.

2. Infection:
Infection is the entry, development, or multiplication of an infectious agent in the human body or animals.

3. Antibiotics:
Antibiotics are metabolic products of microorganisms whose very low concentrations are inhibitory or detrimental to other microbes.

4. Toxin :
The poisonous substances secreted by pathogens that cause diseases are called toxins.

5. Vector:
Vector is an agent that acts as an intermediate carrier of the pathogen.

VIII. Answer in one or two sentences :

Question 1.
What is bacteria?
Answer:
Bacteria are microscopic, single-celled prokaryotic organisms without a nucleus and other cell organelles. >

Question 2.
Differentiate Parasites and Saprophytes.
Answer:
Parasites :
Fungi living on living hosts.

Saprophytes :
Fungi living on dead organic matter.

Question 3.
What is the incubation period?
Answer:
1. The interval between infection and the first appearance of the diseases is called the incubation period.
2. It may vary from few hours to several days.

Question 4.
Differentiate Exotoxins and Endotoxins.
Answer:
Exotoxins :
There are directly secreted by the pathogens.

Endotoxins :
There are released by the disintegration of pathogens.

Question 5.
Why is dengue also known as break-bone fever?
Answer:
The name break bone fever was given because contortions caused intense joint and muscle pain.

Question 6.
What is an immunization?
Answer:
Immunization is a process of developing resistance to infections by administration of antigens (or) antibodies. .

Question 7.
What is TAB?
Answer:
TAB is a combined vaccine for Typhoid, Paratyphi A and Paratyphi B.

Question 8.
Name two diseases transmitted by Aedes aegypti mosquito?
Answer:

1. Chikungunya,
2. Dengue.

Question 9.
What is known as reservior of infection? Give two example.
Answer:
Reservoir of infection are breeding ground for pathogens. E.g. Water, soil.

Question 10.
Differentiate signs and symptoms of disease.
Answer:
Signs :
Signs of disease provide information about particular disease.

Symptoms :
Symptoms are recognizable signs of infectious disease.

Question 11.
Name one disease that is transmitted by houseflies. Mention their causative pathogen.
Answer:
Cholera – Vibrio cholerae (pathogen)

Question 12.
Name the scientist who first discovered penicillin antibiotic. Can you name any other known antibiotic?
Answer:

1. Penicillin was discovered by Alexander Fleming.
2. Other known Antibiotic – Tetracycline.

Question 13.
A baby is suffering from diarrhoea, while other babies in the same locality do not.
Mention the possible causes that you think. What would be the possible solutions for this? »
Answer:

1. Cause for Diarrhoea: Contaminated food (or) water.
2. Possible solutions: Hygienic sanitary condition, Use of Oral Rehydration Solution (ORS).

Question 14.
Sanjay had an attack of chickenpox and has just recovered. The health officer of his locality says that the disease would not occur again for him. What would be the reason for this?
Answer:
While Chicken Pox attacks the first time, it develops immunity for the rest of life.

IX. Short answer questions :

Question 1.
Briefly explain the reproduction of fungi using a flow chart.
Answer:

Question 2.
What is an epidemic disease?
Answer:
Epidemic disease is a disease that breaks out and affects large number of people in a particular geographical region and spreads at the same time. E.g. Influenza.

Question 3.
Differentiate between Infectious and Non-Infectious disease.
Answer:
Infections Disease

1. They are communicable diseases. .
2. They are caused by external factors. Invading of pathogens such as bacteria, virus, vectors, parasites etc.
   E.g. Cholera, Malaria, Chickenpox.

Non-infectious disease

1. They are non-communicable diseases
2. They are caused by internal factors.
   • Malfunctioning of organs,
   • Genetic causes,
   • Hormonal imbalance and
   • Defective Immune system
     E.g. Cancer, Diabetes.

Question 4.
What causes illness?
Answer:
An illness is casual due to a specific infectious agent, capable of being directly or indirectly transmit infection from person to person, animal to animal or from the environment (air, water & food) and insects.

Question 5.
How are respiratory tract infections acquired?
Answer:
Respiratory tract infections are acquired by inhaling air containing the pathogen that is transmitted through droplets caused by cough (or) sneeze, dust, spores, etc.

Question 6.
Name the different species of protozoa plasmodium.
Answer:
The different species of plasmodium are –

1. Plasmodium vivax
2. Plasmodium malariae
3. Plasmodium falciparum
4. Plasmodium ovale.

Question 7.
List the precautionary measures to avoid Avian Influenza.
Answer:
Prevention and Control:

• Avoid open-air markets where infected birds are sold.
• Avoid contact and consumption of infected birds.
• Proper cleaning and cooking of poultry.

Question 8.
Mention the symptoms of poliomyelitis.
Answer:
Symptoms of poliomyelitis :

• Paralysis of limbs and muscles.
• Difficulty in walking.

Question 9.
When Malar, who is suffering from high fever, muscle, and joint pain, undergoes a blood test, it was found that her blood platelet was decreased.
a. What disease is Malar infected with?
b. How is the disease transmitted?
c. How can it be treated?
Answer:
a. Dengue fever.
b. Dengue was caused by a virus which is transmitted by the Aedes aegypti mosquito.
c. Treatment:

• Administer paracetamol to reduce fever and body ache.
• Increase intake of fluid to increase immunity.
• Complete rest for rehabilitation.

Question 10.
How is typhoid prevented and treated?
Answer:
Prevention:

• Contaminated food by flies-and dust should be prevented.
• Basic sanitation and hygienic practices should be improved.

Treatment:
Typhoid should be treated with antibiotic drugs.

Question 11.
We are advised to take bland and nutritious food when we are sick. What is the reason?
Answer:

• Bland and nutritious food are soft, less spicy and low in fibre.
• They are easy digestable and energy giving food. . . .
  Thus, sick person can restore his immunity through bland and nutritious food.

Question 12.
How will you differentiate Hepatitis A from Hepatitis B?
Answer:

Hepatitis A	Hepatitis B
1. Caused by Hepatitis A virus (HAV)	1. Caused by Hepatitis B virus
2. Transmitted through Contaminated water Food Oral route	2. Transmitted through contact (from infected person to a healthy person) Sexual. Blood contact. By surgical equipment (infected needles and syringes). Material (foetal transmission from infected mother to the foetus).
3. Liver is affected in Jaundice (Yellow fever)	3. Cirrhosis of liver.

X. Long Answer question : 

Question 1.
Enumerate the living and non-living characters of virus.
Answer:
1. Living characters of viruses:

• They have nucleic acid DNA or RNA i.e., the genetic material that can replicate.
• They can multiply in the living cells of the host.
• They can attack specific hosts.

2. Non-living characters of viruses:

• Viruses remain as inert material outside their hosts.
• They are devoid of the cell membrane and cell wall.
• They are devoid of cellular organelles like ribosomes, mitochondria, etc.
• They can be crystallised.

Question 2.
Discuss how diseases are categorised.
Answer:
Disease can be catagorized on the basis of:

(i) Extent of occurrence
(ii) Infectious nature
(iii) Type of pathogen
(iv) Transmitting Agent

(i) Extent of occurrence :

• Endemic diseases – Found in the certain geographical area affects the fewer number of people, E.g. Goitre in sub = Himalayan region.
• Epidemic diseases – Disease which breaks out and affects a large number of people in a particular geographical region and spreads at the same time. E.g. Influenza.
• Pandemic disease – Widely distributed on a global scale. E.g. AIDS.
• Sporadic disease – Occasional occurrence of a disease. E.g. Cholera and malaria.

(ii) Infectious nature:

1. Infectious disease are communicable diseases. Caused by external factors pathogenic organisms. E.g. Chickenpox and malaria.

2. Non-Infectious disease:

• Non-communicable diseases.
• Caused by internal factors like :
• Malfunctioning of organs and genetic causes. Hormonal imbalance and immune system defect. E.g. Diabetes, coronary heart diseases, obesity, cancer, goitre etc.

(iii) Types of pathogen :

• Bacterial diseases
• Viral diseases
• Fungal diseases
• Protozoan diseases

(iv) Transmitting agent:

• Airborne diseases: Due to continuous inhalation of contaminated air.
  E.g. Tuberculosis.
• Waterborne diseases: Microbes present in the contaminated water cause various infectious diseases.
  E.g. Cholera, typhoid, etc.
• Vector-borne diseases: Vector is an agent that acts as an intermediate carrier of the pathogen.
  E.g. Malaria, filaria, chikungunya.

Question 3.
Discuss the strategies to adopt to prevent diseases transmitted through mosquitoes.
Answer:

• Prevention of mosquito bites by using mosquito nets mosquito screens, mosquito repellents, and ointments.
• Providing adequate sanitation, underground wastewater disposable system, and drainage of stagnant water to eliminate the breeding places.
• Avoid the collection of water in any uncovered container such as water tanks, pots, flowers, discarded tyres, etc.
• Spraying oil on stagnated water bodies to control mosquito larvae.
• Adult mosquitoes can be killed by spraying insecticides.
• Application of citronella oil (or) eucalyptus oil on the exposed skin.

Question 4.
Amal, a thirteen-year-old boy is suffering from fever, headache, body pain, vomiting, and diarrhoea. He finds it difficult to breathe.

1. Diagnose the disease.
2. What is the causative agent?
3. What prevention and control measures can be taken?

Answer:

1. Diagnosed Disease: Swine flu.
2. Causative agent: InfluerKa virus H1N1
3. Prevention and control:
   • Administration of nasal spray vaccine.
   • Avoiding close contact with a person suffering from the flu.
   • Intake of water and fruit juices will help prevent dehydration.
   • Plenty of rest will help the body fight infection.
   • Always wash hands regularly and practice good hygiene.

Question 5.
Name the causative agent of typhoid in humans. How does the pathogen gain entry into the human body? Write the diagnostic symptoms and mention the organ that is affected in severe cases.
Answer:

• Causative agent of typhoid: Salmonella Typhi (Bacteria)
• The entry of Pathogen: Food and water contaminated by the faeces of an infected person through houseflies.
• Diagnostic symptoms: Fever, weakness, and vomiting.
• Affected organ: Small Intestine.

Question 6.
Some human diseases are transmitted only when the blood of a patient comes in close contact with the blood of a healthy person. In one such disease, there is a progressive decrease in WBC of the patient.

1. Name the disease and its causative agent.
2. Name the type of WBC affected during infection.
3. How does the blood of a patient come in contact with the blood of a healthy patient?
4. Suggest three methods that help in preventing such infection.

Answer:

1. Disease Name Causative agent: AIDS (Acquired Immuno Deficiency Syndrome).
2. Affected WBC type: Human Immunodeficiency Virus (HIV)
3. Contact of blood: Lymphocytes (T-lymphocytes)
4. Prevention methods: Transfusion of unscreened blood (blood contact).
   • Usage of disposable syringes and needles.
   • Screening of blood before blood transfusion.
   • Avoid sharing shaving blades/razors.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 13 Chemical Bonding Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Chapter 13 Chemical Bonding

9th Science Guide Chemical Bonding Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Number of valence electrons in carbon is
(a) 2
(b) 4
(c) 3
(d) 5
Answer:
(b) 4

Question 2.
Sodium having atomic number 11, is ready to ______________ electron/electrons to attain the nearest noble gas electronic configuration.
(a) gain one
(b) gain two
(c) lose one
(d) lose two
Answer:
(c) lose one

Question 3.
The element that would form anion by gaining electrons in a chemical reaction is ………………..
(a) potassium
(b) calcium
(e) fluorine
(d) iron
Answer:
(c) fluorine

Question 4.
Bond formed between a metal and non metal atom is usually …………………..
(a) ionic bond
(b) covalent bond
(e) co-ordinate bond
Answer:
(a) ionic bond

Question 5.
______________ compounds have high melting and boiling points.
(a) Covalent
(b) Coordinate
(e) Ionic
Answer:
(c) Ionic

Question 6.
Covalent bond is formed by …………………
(a) transfer of electrons
(b) sharing of electrons
(c) sharing a pair of electrons
Answer:
(b) sharing of electrons

Question 7.
Oxidising agents are also called as …………………. because they remove eletrons form other substances.
(a) electron donors
(b) electron acceptors
Answer:
(b) electron acceptors

Question 8.
Elements with stable electronic configurations have eight electrons in their valence shell. They are ……………….
(a) halogens
(b) metals
(c) nobel gases
(d) non metals
Answer:
(c) noble gases

II. Answer briefly :

Question 1.
How do atoms attain Noble gas electronic configuration?
Answer:
Atoms of all elements, other than inert gases, combine to form molecules because they have incomplete valence shell and tend to attain a stable electronic configuration similar to noble gases. Atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to achieve the stable outer shell of eight electrons.

Question 2.
NaCl is insoluble in carbon tetrachloride but soluble in water. Give reason.
Answer:
NaCl is an ionic compound, it is soluble in polar solvent (water). Whereas CCl₄ is a covalent compound. So.it is insoluble in polar solvent (water). But it is soluble in nonpolar solvents.

Question 3.
Explain the Octet rule with an example.
Answer:
The tendency of atoms to have eight electrons in the valence shell is known as the ‘Octet rule’ or the ‘Rule of eight’ For example, Sodium with atomic number 11 will readily loose one electron to attain Neon’s stable electronic configuration. Similarly, chlorine has electronic configuration 2,8,7. To get the nearest noble gas (i.e. Argon) configuration, it needs one more electron. So chlorine readily gains one electron from another atom and obtains stable electronic configuration. Thus elements tend to have stable valence shell (eight electrons) either by losing or gaining electrons.

Question 4.
Write a note on different types of bonds.
Answer:
There are different types of chemical bonding possible between atoms which make the molecules. Depending on the type of bond they show different characteristics or properties.

Question 5.
Correct the wrong statements.
(a) Ionic compounds dissolve in non-polar solvents.
(b) Covalent compounds conduct electricity in molten or solution state.
Answer:
(a) Covalent compounds dissolve in non-polar solvents. (or) Ionic compounds dissolve in polar solvents.
(b) Ionic compounds conduct electricity in molten or solution state.

Question 6.
Complete the table given below.

Answer:

Question 7.
Draw the electron distribution diagram for the formation of Carbon dioxide (CO₂) molecule.
Answer:

Question 8.
Fill in the following table according to the type of bonds formed in the given molecule.
CaCl₂, H₂O, CaO, CO, KBr, HCl, CCl₄, HF, CO₂, Al₂Cl₆

Answer:

Question 9.
The property which is characteristic of an Ionic compound is that
(a) it often exists as a gas at room temperature.
(b) it is hard and brittle.
(c) it undergoes molecular reactions
(d) it has a low melting point.
Answer:
(b) it is hard and brittle

Question 10.
Identify the following reactions as oxidation or reduction.
(a) Na → Na⁺ + e^–
(b) Fe³⁺ + 2 e^– → Fe⁺
Answer:
(a) oxidation
(b) reduction

Question 11.
Identify the compounds as Ionic/Covalent/Coordinate based on the given characteristics.
(a) Soluble in non-polar solvents
(b) Undergoes faster/instantaneous reactions
(c) Non-conductors of electricity
(d) Solids at room temperature
Answer:
(a) Co-ordinate Covalent compound.
(b) Ionic compound.
(c) Covalent compound.
(d) Ionic compound.

Question 12.
An atom X with atomic number 20 combines with atom Y with atomic number 8. Draw the dot structure for the formation of the molecule XY
Answer:

Question 13.
Considering MgCl₂ as ionic compound and CH₄ as covalent compound give any two differences between these two compounds.
Answer:

MgCl (ionic compound)	CH4(covalent compound)
1. It is formed by the transfer of electrons (2e– ) from metal magnesium (Mg) to a non – metal atom chlorine (Cl)	It is formed by the sharing of electrons between the non-metal atoms carbon and hydrogen
2. In MgCl2 , strong electrostatic force of attraction exist between magnesium cation (Mg2+) and chlorine atoms (Cl– )	In CH4, weak force of attraction exist between the carbon atom and four hydrogen atoms.

Question 14.
Why are Noble gases inert in nature?
Answer:
Noble gases are inert in nature due to the completely filled subshells and thus have stable electronic structures which is very difficult to change. The elements Helium, Neon, Argon, Krypton, Xenon and Radon of group 18 in the periodic table are Noble gases.

III. Answer in detail :

Question 1.
List down the differences between Ionic and Covalent compounds.
Answer:

Ionic Compounds	Covalent Compounds
Formed by the transfer of electrons from a metal to a non-metal atom	Formed by sharing of electrons between non-metal atoms.
The strong electrostatic force of attraction between cations and anions.	Mutual sharing of electrons and so weak force of attraction between atoms.
Solids at room temperature.	Gases, liquids, and soft solids.
Conducts electricity in molten state or in solutions	Non-conductors of electricity.
Have high melting and boiling points.	Have low melting and boiling points.
Soluble in polar solvents	Soluble in non-polar solvents.
Hard and brittle.	Soft and waxy.
Undergo ionic reaction which is fast and instantaneous	Undergo molecular reactions which are slow.

Question 2.
Give an example for each of the following statements.
(a) A compound in which two Covalent bonds are formed.
(b) A compound in which one ionic bond is formed.
(c) A compound in which two Covalent and one Coordinate bond are formed.
(d) A Compound in which three covalent bonds are formed.
(e) A compound in which a coordinate bond is formed.
Answer:
(a) Oxygen molecule (O₂) (O = O)
(b) Sodium’Chloride (NaCl)
(c) Carbon monoxide?

(d) Nitrogen molecule (N₂) (N ≡N)
(e) NH₃ → BF₃

Question 3.
Identify the incorrect statement and correct them.
(a) Like covalent compounds, coordinate compounds also contain charged particles (ions). So they; are good conductors of electricity.
(b) Ionic bond is a weak bond when compared to Hydrogen bond.
(c) Ionic or electrovalent bonds are formed by the mutual sharing of electrons between atoms.
(d) Loss of electrons is called Oxidation and gain of the electron is called Reduction.
(e) The electrons which are not involved in bonding are called valence electrons.
Answer:
(a) Incorrect statement. Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(b) Incorrect statement. An ionic bond is a strong bond when compared to a hydrogen bond.
(c) Incorrect statement. Covalent bonds are formed by the mutual sharing of electrons between atoms, (or) Ionic or electrovalent bonds are formed by the transfer of electrons between atoms.
(d) Correct statement
(e) Incorrect statement. The electrons which are not involved in bonding are called lone pair of electrons.

Question 4.
Discuss in brief the properties of coordinate covalent compounds.
Answer:
The compounds containing coordinate covalent bonds are called coordinate compounds.
(a) Physical state – These compounds exist as gases, liquids or solids.
(b) Electrical conductivity-Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(c) Melting point – These compounds have to melt and boiling points higher than those of purely covalent compounds but lower than those of purely ionic compounds.
(d) Solubility – Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CCl₄, and toluene.
(e) Reactions – Co-ordinate covalent compounds undergo molecular reactions which are slow.

Question 5.
Find the oxidation number of the elements in the following compounds.
(a) C in CO₂
(b) Mn in MnSO₄
(c) N in HNO₃
Answer:
(a) C in CO₂
1(C) + 2(0) = 0
1x + 2(-2) = 0
x-4 = 0 ‘
x = +4 .
ON of C in CO₂ is +4

(b) Mn in MnSO₄
1 (Mn) + 1 (S) + 4(0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x – 2 = 0
x = +2
ON of Mn in MnSO₄ is +2,

(c) N in HNO₃
1(H) + 1 (N) +3(0) =0
1 (+1) + 1 (x) + 3 (-2) =0
+ 1 + x – 6 =0
x – 5 =0
x = +5
ON of N in HNO₃ is + 5.

9th Science Guide Chemical Bonding Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following atom can exist independently?
(a) Magnesium
(b) Chlorine
(c) Hydrogen
(d) Neon
Answer:
(d) Neon

Question 2.
Alkali and alkaline earth metals form ………… compound when they react with non-metals.
(a) ionic
(b) covalent
(c) co-ordinate covalent
(d) all the above
Answer:
(a) ionic

Question 3.
……………..compounds are highly brittle.
(a) Ionic
(b) Covalent
(c) Co-ordinate covalent
Answer:
(a) Ionic

Question 4.
The bond which is formed by mutual sharing of electrons is called ……………….. bond.
(a) ionic
(b) covalent
(c) co-ordinate covalent bond
(d) all the above
Answer:
(b) covalent

Question 5.
………………. is an example of a covalent compound having a high melting point.
(a) Magnesium oxide
(b) Silicon carbide
(c) Ammonia
(d) All the above
Answer:
(b) Silicon carbide

Question 6.
Which of the following compound(s) possesses a high melting point?
(a) NaCl
(b) MgCl₂
(c) CCl₄
(d) Both a & b
Answer:
(d) Both a & b

Question 7.
The element that would form cation due to the loss of electron during the chemical reaction is ………………..
(a) calcium
(b) Fluorine
(c) Chlorine
(d) all the above
Answer:
(a) calcium

Question 8.
Fajan’s rule is formulated by considering …………… the cation and ………………..of the cation and anion.
(a) charge
(b) size
(c) charge & size
(d) none
Answer:
(c) charge & size

Question 9.
The formation of brown colour on the freshly unit surface of vegetables and fruits is because ………………. of organic compounds present in them.
(a) oxidation
(b) reduction
(c) both a & b
(d) none
Answer:
(a) oxidation

Question 10.
Which of the following compounds has melting and boiling points higher than covalent compounds but lower than ionic compounds?
(a) NaCl
(b) MgCl₂
(c) H₂O
(d) NH₃→BF₃
Answer:
(d) NH₃→BF₃

Question 11.
Atoms having 1,2 or 3 electrons in their valence shell will readily form ……………..
(a) cation
(b) anion
Answer:
(a) cation

II. Fill in the blanks:

1. ……………theory explains the formation of molecules.
Answer:
Kossel – Lewis theory

The valency of noble gases is ……………..
Answer:
zero

3. …………….. is the only noble gas which does not have eight electrons in their valence shell.
Answer:
Helium

4. The atom that loses electrons will from a ________
Answer:
cation

5. ______ compounds have high density.
Answer:
Ionic

6. In covalent bond formation, the sharing of ………….. electrons takes place in their outermost shell.
Answer:
unpaired

7. Polar solvents contain bond between atoms with ………………
Answer:
different electronegativities

8. ……………….. & ………….. atoms have similar electronegativities.
Answer:
Carbon & hydrogen

9. Molecular reactions are ……………… in the covalent compound.
Answer:
slow

10. Ionic compounds are ……………..in nature.
Answer:
solid

11. The tendency of atoms to have eight electrons in the outer shell is known as ……………….
Answer:
Octet rule

12. As per Fajan’s rule, A1I₃is ……………..
Answer:
covalent

13. Oxidising agents are otherwise called as ………………..
Answer:
electron acceptors

14. The tarnishing of metals is due to the formation of ……………….
Answer:
metal oxide

15. The tarnishing of metals is an example of ……………. reaction.
Answer:
oxidation

16. The sum of oxidation number of all atoms in a compound is ………………..
Answer:
Zero

17. The ……………….. is a metal that has a high resistance to corrosion.
Answer:
Gold

III. Spot the error / correct the wrong statement:

Question 1.
In the formation of compounds, the inner shell electrons of an atom involved in bonding.
Answer:
In the formation of compounds, the valence electrons of an atom involved in bonding.

Question 2.
The atom that gains electrons will form a cation.
Answer:
The atom that gains electrons will form an anion.

Question 3.
Ionic compounds have low melting and boiling point.
Answer:
Ionic compounds have high melting and boiling point, (or) Covalent compounds have low melting and boiling point.

Question 4.
Non-polar solvents contain bonds between atoms with different electronegativities.
Answer:
Non-polar solvents contains bonds between atoms with similar electronegativities.

Question 5.
Covalent compounds are soluble in polar solvents.
Answer:
Covalent compounds are readily soluble in non-polar solvents, (or) Ionic compounds are soluble in polar solvents.

Question 6.
Greater the charge of the cation greater will be the ionic character.
Answer:
Greater the charge of the cation greater will be the covalent character.

IV. Match the following :

Question 1.

1) Monoatomic gaseous atom	a) Electrovalent bond
2) Octet rule	b) Benzene
3) Ionic bond	c) Water
4) Non-polar solvent	d) Electronic theory of valence
5) Polar solvent	e) Noble gases

Answer:
1. – e, 2. – d, 3. – a, 4. – b, 5. – c

Question 2.

1) Atomic bond	a) Oxygen and hydrogen
2) Atoms with different electronegativities	b) acceptor bond
3) Atom which accepts electron pair	c) covalent bond
4) Rusting of iron	d) donor atom
5) Atom which provides electron pair	e) oxidation
	f) ionic bond

Answer:
1. – c, 2. – a, 3. – b, 4. – e, 5, – d.

V. Find the odd one out and write the reason:

Question 1.
Water, acetone, benzene, toluene turpentine.
Answer:
Water. It is a polar solvent where a^ others air non-polar solvents.

Question 2.
Addition of oxygen, removal of hydrogen, loss of an electron, gain of electron.
Answer:
Gain of electron. It is a reduction reaction whereas other three are oxidation reactions.

Question 3.
Platinum, palladium NaBH₄, CrO₃.
Answer:
CrO₃ It is an oxidising agent whereas the other three are reducing agents.

Question 4.
Ionic bond, metallic bond, Coordinate covalent bond, Hydrogen bond.
Answer:
Hydrogen bond. It is a weak bond whereas the other three are strong bonds.

Question 5.
Soft & waxy, a bad conductor of electricity, low boiling point, solid at room temperature.
Answer:
Solid at room temperature.
It is the property of ionic compounds whereas the other three are the properties of covalent compounds.

.
VI. Answer in brief :

Question 1.
What is a chemical bond?
Answer:
A chemical bond may be defined as the force of attraction between the two atoms that bind them together as a unit called a molecule.

Question 2.
Write the basic concept of Kossel – Lewis theory.
Answer:
Kossle – Lewis theory is based on the concept of electronic configuration of noble gases.

Question 3.
Define the ionic bond.
Answer:
An ionic bond is a chemical bond formed by the electrostatic attraction between positive and negative ions. The bond is formed between two atoms when one or more electrons are transferred from the valence shell of one atom to the valence shell of the other atom.

Question 4.
The following shows the electronic distribution diagram for the formation of MgCl₂ molecule. Based on this answer the following questions.

(a) Which of the above atom loses electrons to form a cation?
(b) Which of the above atom gain electrons to form an anion?
(c) How many electrons are transferred from Mg to Cl?
(d) Write the name of the anion formed.
(e) Which noble gas configuration do these ions resemble?
(f) Write the electronic configuration of Mg²⁺ & Cl^–
Answer:
(a) Magnesium atom loses electrons to form a cation.
(b) Chlorine atom gains 1 electron to from anion.
(c) Two electrons are transferred from Mg – atom to 2 Cl – atoms (each Cl – atom gains 1e^– from Mg – atom).
(d) Chloride anion (Cl^– )
(e) Mg²⁺ ion resembles noble gas configuration of Neon Cl^– ion resembles noble gas configuration of Argon.
(f) Electronic configuration of Mg²⁺ is 2, 8. and Electronic configuration of Cl^– is 2, 8, 8.

Question 5.
What is covalent bond?
Answer:
Bond which is formed between atoms by the mutual sharing of electrons is known as a covalent bond.

Question 6.
Name of the following:
(a) An element which obtains the noble gas configuration of neon by losing three electrons.
(b) An element which gains two electrons to obtain the noble gas configuration of Neon.
Answer:
(a) Aluminium (Al → Al³⁺ + 3e^–)
(b) Oxygen atom (O + 2e^– → 0^2-)

Question 7.
Identify the following reactions as oxidation/reduction/redox reaction.
(a) Zn + CuSO₄ → Cu + ZnSO₄
(b) CuO+H₂ → Cu+H₂O
(c) 2Mg +O₂  → 2MgO
Answer:
(a) Redox reaction
(b) Reduction
(e) Oxidation

Question 8.
What are oxidising agents? Give an example.
Answer:
Substances which have the ability to oxidise other substances are called oxidizing agents. These are also called electron acceptors because they remove electrons from other substances. ’
Example:

Question 9.
What are reducing agents? Give examples.
Answer:
Substances which have the ability to reduce other substances are called reducing agents. These are also called electron donors because they donate electrons to other substances.
Example: NaBH₄, LiAlH₄ and metals like Palladium, Platinum.

Question 10.
What are redox reactions? Give examples.
Answer:
Both the oxidation and reduction occurs in the same reaction simultaneously is known as a redox reaction. If one reactant gets oxidised, the other gets reduced. Such reactions are called oxidation-reduction reactions or redox reactions.
Ex. 1 : 2 PbO + C → 2 Pb + CO₂
Ex. 2 : Zn + CuSO₄  → Cu + ZnSO₄

Question 11.
Define (a) oxidation (b) reduction reactions : Give examples.
Answer:

Question 12.
What is rancidity?
Answer:
The oxidation reaction in food materials that were left open for a long period is responsible for spoiling of food. This is called rancidity.

Question 13.
Define oxidation number.
Answer:
Oxidation number of an element is defined as the formal charge which an atom of that element appears to have when electrons are counted.

Question 14.
Identify the type of bond in \(\mathrm{NH}_{4}^{+}\)

Answer:

VII. To interpret:

Question 1.
Ionic bond is also called electrostatic bond.
Answer:
In ionic bond formation the bond is formed between the oppositely charged ions and these ions come closer to each other due to electrostatic force of attraction. So ionic bond is also called an electrostatic bond.

Question 2.
Ionic compounds are crystalline solids at room temperature.
Answer:
Ionic compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.

Question 3.
Covalent compounds have a low melting point.
Answer:
In covalent compounds, atoms are held by a weak force of attraction. When heat is applied, the molecules are readily pulled out and get free movement.

VIII. Assertion and Reason type questions :

Question 1.
Statement (A) : Ionic compounds do not conduct electricity in a solid-state.
Reason (B) : The ions in ionic compounds are tightly held together by a strong electrostatic force of attraction and they can not move freely.
(a) B explains A
(b) B does not explain A
(c) B is wrong A
(d) A is right B is wrong
Answer:
(a) B explains A

Question 2.
Statement (A) : Covalent compounds are bad conductors of electricity.
Reason (B) : Covalent compounds contain charged particles (ions)
a) B explains A
b) B does not explain A
c) Both A & B are right
d) Both A & B are wrong
Answer:
(b) B does not explain A
Reason: Since covalent compounds do not have charged particles (ions), they are bad conductors of electricity.

IX. Find the oxidation number of the elements in the following compounds.

(1) Zn in ZnSO₄
(2) Ca in CaH₂
(3) Mg in MgO
(4) N in NH₃
(5) A1 in AlCl₃
Answer:
(1) ZnSO₄
1(Zn) + 1 (S) + 4 (0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x = + 2
Oxidation number of Zn in ZnSO₄ is +2

(2) CaH₂
1(Ca) + 2 (H) = 0
x + 2 (-1) = 0
x -2 = 0
x = + 2
Oxidation number of Ca in CaH₂ is +2

(3) MgO
1(Mg) + 1 (O) = 0
x + 1 (-2) = 0
x -2 = 0
x = + 2
Oxidation number of Mg in MgO is +2

(4) NH₃
1(N) + 3 (H) = 0
x + 3 (-1) = 0
x – 3 = 0
x = +3
Oxidation number of N in NH₃ is +3
(5) AlCl₃
1(Al) + 3(Cl) = 0
x + 3 (-1) = 0
x – 3 = 0
x = + 3
Oxidation number of Al in AlCl₃ is +3

X. Complete the following table:

Question 1.

Atoms	Atomic number	Electron distribution
a) O	8	–
b) N	–	–
c) –	17	–
d) –	–	2,8,2

Answer:

Atoms	Atomic number	Electron distribution
a) O	8	2,6
b) N	7	2,5
c) Cl	17	2,8,7
d) Mg	12	2,8,2

Question 2.

a) Dativebond	–
b) CaH2 → Ca+H2	–
c) –	Reduction
d) –	Redox reaction

Answer:

a) Dativebond	Co-ordinate covalent bond
b) CaH2 → Ca+H2	Oxidation
c) Fe3+ + e– →Fe2+	Reduction
d) both Oxidation of Reduction takes place simultaneously	Redox reaction

XI. To Match:

Name of compound	Type of compound
a) Sodium chloride	?
b) ?	co-ordinate covalent compound
c) Methane	?
d) Fluorine molecule	?

Answer:

Name of compound	Type of compound
a) Sodium chloride	Ionic compound
b) NH3 → BF3	co-ordinate covalent compound
c) Methane	Covalent compound
d) Fluorine molecule	Covalent compound

XII. Answer in detail :

Question 1.
Explain the ionic bond formation in sodium chloride with electron distribution diagram.
Answer:
Formation of Sodium Chloride (NaCl)

(i) The atomic number of Sodium is 11 and its electronic configuration is 2, 8, 1. It has one electron excess to the nearest stable electronic configuration of a noble gas – Neon.

(ii) So sodium has a tendency to lose one electron from its outermost shell and acquire a stable electronic configuration forming sodium cation (Na⁺).

(iii) The atomic number of chlorine is 17 and its electronic configuration is 2, 8, 7. It has one electron less to The nearest stable electronic configuration of a noble gas – Argon.

(iv) So chlorine has a tendency to gain one electron to acquire a stable electronic
configuration forming chloride anion (Cl^–)

(v) When an atom of sodium combines with an atom of chlorine, an electron is transferred from the sodium atom to chlorine atom forming sodium chloride molecule. Thus both the atoms achieve stable octet electronic configuration.

Question 2.
Explain the covalent bond formation in the following molecules.
(a) Chlorine
(b) Nitrogen
(c) Hydrogen
(d) Oxygen
Answer:
(a) Chlorine
Chlorine molecule is formed by two chlorine atoms. Each chlorine atom has seven valence electrons (2,8,7). These two atoms achieve a stable completely filled electronic configuration (octet) by sharing a pair of electrons.

(b) Nitrogen
Nitrogen molecule is formed by two nitrogen atoms. Each nitrogen atom has five valence electrons (2, 5). These two atoms achieve a stable completely filled electronic configuration (octet) by sharing three pair of electrons. Hence a triple bond is formed in between the two atoms.

(c)Hydrogen
Hydrogen molecule is formed by two hydrogen atoms. Both hydrogen atoms contributes one electron each to the shared pair and both atoms acquire stable completely filled electronic configuration.

(d) Oxygen
Oxygen molecule is formed by two oxygen atoms. Each oxygen atom has six valence electrons (2,6). These two atoms achieve a stable electronic configuration (octet) by sharing two pair of electrons. Hence a double bond is formed in between
the two atoms.

Question 3.
Explain the co-ordinate covalent bond formation in between NH₃ → BF₃ molecules.
Answer:
The ammonia molecule gives a lone pair of electrons to boron trifluoride (BF₃) molecule which is electron deficient. Thus a coordinate covalent bond is formed between NH₃ (donor molecule) and BF₃ (acceptor molecule) and is represented by

Question 4.
Write notes on the characteristics of covalent compounds.
Answer:
a. Physical state: Depending on the force of attraction between covalent molecules the bond may be weaker or stronger. Thus covalent compounds exist in gaseous, liquid, and solid forms. Eg. Oxygen-gas; Water-liquid: Diamond-solid.

b. Electrical conductivity: Covalent compounds do not contain charged particles (ions), so they are bad conductors of electricity.

c. Melting point: Except few covalent compounds (Diamond, Silicon carbide), they have relatively low melting points compared to Ionic compounds.

d. Solubility: Covalent compounds are readily soluble in non-polar solvents like benzene (C₆H₆), carbon tetrachloride (CCl₄). They are insoluble in polar solvents like water.

e. Hardness and brittleness: Covalent compounds are neither hard nor brittle. But they are soft and waxy.

f. Reactions: Covalent compounds undergo molecular reactions in solutions and these reactions are slow.

Question 5.
Write notes on the characteristics of ionic compounds.
Answer:
a. Physical state: These compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.

b. Electrical conductivity: Ionic compounds are crystalline solids and so their ions are tightly held together. The ions, therefore, cannot move freely, so they do not conduct electricity in a solid-state. However, in a molten state and their aqueous solutions conduct electricity.

c. Melting point: the strong electrostatic force between the cations and anions hold the ions tightly together, so very high energy is required to separate them. Hence ionic compounds have high melting and boiling points.

d. Solubility: Ionic compounds are soluble in polar solvents like water. They are insoluble in non-polar solvents like benzene (C₆H₆), carbon tetrachloride (CCl₄).

e. Density, hardness, and brittleness: Ionic compounds have high density and they are quite hard because of the strong electrostatic force between the ions. But they are highly brittle.

f. Reactions: Ionic compounds undergo ionic reactions which are practically rapid and instantaneous.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 10 Matter Around Us Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 10 Matter Around Us

9th Science Guide Matter Around Us Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
The separation of denser particles from lighter particles done by rotation at high speed is called ………………
(a) Filtration
(b) sedimentation
(c) decantation
(d) centrifugation
Answer:
(d) centrifugaton

Question 2.
Among the following ……………… is a mixture.
(a) Common Salt
(b) Juice
(c) Carbon dioxide
(d) Pure Silver
Answer:
(b) Juice

Question 3.
When we mix a drop of ink in water we get a . ………………
(a) Heterogeneous Mixture
(b) Compound
(c) Homogeneous Mixture
(d) Suspension
Answer:
(c) Homogeneous Mixture

Question 4.
……………….is essential to perform separation by solvent extraction method.
(a) Separating funnel
(b) filter paper
(c) centrifuge machine
(d) sieve
Answer:
(a) Separating funnel

Question 5.
………………… has the same properties throughout the sample.
(a) Pure substance
(b) Mixture
(c) Colloid
(d) Suspension
Answer:
(a) Pure substance

II. State whether true or false. If false, correct the statement.

1. Oil and water are immiscible in each other.
Answer:
True.

2. A compound cannot be broken into simpler substances chemically.
Answer:
False
Correct statement: A compound can be broken into simpler substances chemically.

3. Liquid – liquid colloids are called gels
Answer:
False.
Correct statement: Liquid – solid colloids are called gels.

4. Buttermilk is an example of heterogeneous mixture.
Answer:
True.

5. Aspirin is composed of 60% Carbon, 4.5% Hydrogen and 35.5% Oxygen by mass. Aspirin is a mixture.
Answer:
False.
Correct statement: It is Compound. It is because the components are combined in a fixed ratio by mass.

III. Match the following :

A	B
Element	Settles down on standing
compound	Impure substance
Colloid	Made up of molecules
Suspension	Pure substance
Mixture	Made up of atoms

Answer:

A	B
Element	Pure substance
compound	Made up of atoms
Colloid	Made up of molecules
Suspension	Settles down on standing
Mixture	Impure substance

IV. Fill in the blanks :

1. A …………………. mixture has no distinguishable boundary between its components.
Answer:
Homogeneous

2. An example of a substance that sublimes is…………
Answer:
Dry ice / Solid CO₂ / Camphor

3. Alcohol can be separated from water by ………….
Answer:
Fractional distillation

4. In petroleum refining, the method of separation used is ………….
Answer:
Fractional distillation

5. Chromatography is based on the principle of………….
Answer:
different solubilities

V. Very Short answer :

Question 1.
Differentiate between absorption and adsorption.
Answer:
Absorption

1. Absorption is the process in which the substance is dissolved throughout the bulk of another substance.
2. For example a paper (absorbent) soaks up or absorbs water.

Adsorption

1. Adsorption is the process in which particles of a substance, (it could be gas, liquid or dissolved solid) adhere to a surface of another substance.
2. For example: charcoal adsorbs gases on its surface. Charcoal is called the adsorbent and the gas is called the adsorbate.

Question 2.
Define Sublimation.
Answer:
Certain solids change directly to a gas without passing through the liquid is called sublimation.

Question 3.
A few drops of ‘DettoP when added to water the mixture turns turbid. Why?
Answer:
The Dettol formulation is a stabilised micro-emulsion. It is manufactured using Chloroxylenol 4.8% and the rest made up by pine oil, isopropanol, castor oil, and soap. On dilution with water, the micro-emulsion destabilises releasing the pine oil and castor oil as a visible bloom. That is why the mixture turns turbid.

Question 4.
Name the apparatus that you will use to separate the components of mixtures containing two, i. miscible liquids, ii. immiscible liquids.
Answer:

1. Miscible liquids – Fractional distillation (Fractionating column and Liebig) Condenser
2. Immiscible liquids – Separating funnel

Question 5.
Name the components in each of the following mixtures.

1. Ice cream
2. Lemonade
3. Air
4. Soil

Answer:

1. Ice cream is a mixture of cream, milk, sugar & sometimes egg.
2. Lemonade is a mixture of lemon juice, sugar and water.
3. Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour, and other gases.
4. Soil is a mixture of clay, sand and various salts.

VI. Answer briefly

Question 1.
Which of the following are pure substances?
Ice, Milk, Iron, Hydrochloric acid, Mercury, Brick, and Water.
Answer:
Ice, Iron, Hydrochloric acid, Mercury, and water are pure substances.

Question 2.
Oxygen is very essential for us to live. It forms 21 % of air by volume. Is it an element or a compound?
Answer:
Oxygen is an element.

Question 3.
You have just won a medal made of 22-carat gold. Have you just procured a pure substance or impure substance?
Answer:
I have procured an impure substance. It is made of 22 parts of pure gold and 2 parts of copper or silver.

Question 4.
How will you separate a mixture containing sawdust, naphthalene and iron filings?
Answer:
The iron filings in the mixture can be separated by Magnetic separation and Naphthalene by sublimation. Sawdust will be remaining at the bottom.

Question 5.
How are homogenous solutions different from a heterogeneous solutions? Explain with examples.
Answer:
Homogeneous mixtures

1. Components are uniformly mixed and it will have a single phase,
   Eg: Alloys, salt solution, lemonade, petrol etc.
2. No boundaries of separation between the components. Has a single phase.
3. Components are not visible to the naked eye.
4. They will be in solid, liquid or in the gaseous phase.

Heterogeneous mixtures

1. Components are not uniformly mixed and it will have more than a single phase. They are called suspensions. Eg: chalk in water, petrol in water, sand in water, etc.
2. There are visible boundaries between the components. Have two or more distinct phases.
3. Components are visible to the naked eye.
4. Can be a solid-liquid or solid-gas or liquid-gas or solid-solid, or liquid-liquid mixtures.

VII. Answer in detail:

Question 1.
Write the differences between elements and compounds and give an example for each.
Elements

1. Contains only one kind of atoms.
2. It is a pure substance.
3. Cannot be broken down further into to simpler substances by chemical methods.
4. Has definite physical and chemical properties.
5. Eg., Copper (Cu), Silicon (Si), Gold (Ag)

Compounds

1. Contains more than one kind of atoms.
2. It is not a pure substance.
3. Can be broken down further into simpler substances by chemical methods.
4. Has definite physical and chemical properties.
5. Eg., Water (H₂0), Carbon dioxide (CO₂), Ammonia (NH₃)

Question 2.
Explain the Tyndall effect and Brownian movement with a suitable diagram.
Answer:
Brownian Movement:
Brownian movement is a kinetic property. When colloidal solutions are viewed under a powerful microscope,it can be seen that colloidal particles are moving constantly and rapidly in zig-zag directions.

The Brownian movement of particles is due to the unbalanced bombardment of the particles by the molecules of the dispersion medium.

Tyndall effect:

• Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution, the path of the beam becomes visible.
• This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone.
• This phenomenon is not observed in case of true solution.
  
• This phenomenon is due to scattering of light by colloidal particles.

Question 3.
How is a mixture of common salt, oil, and water separated? You can use a combination
of different methods.
Answer:

• The mixture is taken in a separating funnel., whose mouth is kept closed.
• Oil and water are immiscible liquids.
• As common salt can dissolve in water it settles as a separate layer at the bottom of the oil layer in the separating funnel.
• Place a beaker below the funnel to collect salt solution.
• Open the tap. Allow the salt solution alone to collect in the beaker.
• From the salt solution, common salt is obtained from evaporation.

Intext Activities

ACTIVITY – 1

1. Is air a pure substance or Mixture? Justify
2. You must have seen brass statues in museums and places of worship. Brass is an alloy made up of approx. 30% zinc and 70% copper. Is Brass a pure substance or a mixture or compound?
Answer:
1. Air is a mixture.
Reason: Air contains nitrogen, oxygen, carbon dioxide, dust particles, water vapour. The composition of air is not the same at all places.
2. Brass is a mixture of solid in solid.

ACTIVITY – 3

Take some powdered iron filings and mix them with sulphur.
i. Divide the mixture into two equal halves.
ii. Keep the first half of the mixture as it is, but heat the second half of the mixture.
iii. On heating you will get a black brittle compound.

Solution:

• When Iron fillings and sulphur are mixed both retain their properties it means they have not undergone any chemical reaction.
  Iron + Sulphur → dirty yellow powder
• When Iron fillings and sulphur are mixed and heated, they undergo a chemical reaction and form Iron sulphide
  
• The black brittle compound is iron sulphate.

ACTIVITY – 4

Identify whether the given substance is a mixture or compound and justify your answer.
1. Sand and water, 2.Sand and iron filings, 3.Concrete, 4. Water and oil, 5. Salad, 6. Water 7. Carbon dioxide, 8. Cement, 9. Alcohol.
Solution :

Substance	Mixture/ compound
1. Sand and water	Mixture – No chemical alteration of two components.
2. Sand and iron filings	Mixture – Sand (silicon and oxygen) is a compound, but sand with iron filings form a mixture.
3. Concrete	Mixture – Concrete is a mixture of lime, cement, water, sand, and other rocks.
4. Water and oil	Mixture – Water is a compound, but when water is mixed with oil, it forms a heterogeneous mixture.
5. Salad	Mixture – salad consists of two or more substances mixed together without any chemical bond.
6. Water	Compound – (2-H and 1-O) Both combining elements are mixed chemically.
7. Carbon dioxide	Compound – (1-C and 2-O) Both combining elements are mixed chemically.
8. Cement	Mixture – Cement is a mixture of many compounds.
9. Alcohol	Compound – It is an organic compound in which one the hydroxyl group is bound to a saturated/unsaturated carbon atom.

ACTIVITY – 5

1. Take bottles containing sugar, starch, and wheat flour.
2. Add one teaspoon full of each one to a glass of water and stir well. Leave it aside for about ten minutes.
What do you observe?
Answer:

When one teaspoon full of sugar, starch and wheat flour are added to a glass of water, sugar dissolves in water but wheat flour does not. If we leave it aside for about 10 minutes, wheat flour settles at the bottom

Test Yourself :

Question 1.
Why whole milk is white?
Answer:
Milk is white because it reflects all wavelengths of visible light. The mixture of reflected colors produces white light. The reason for this is due to the chemical composition of milk and the size of the particles contained within it.

Question 2.
Why the ocean is blue?
Answer:
The ocean looks blue because red, orange, and yellow (long-wavelength light) are absorbed more strongly by water than is blue (short-wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue.

Question 3.
Why the sun looks yellow when it is really not?
Answer:
Our sun is actually white (a mixture of all wavelength of visible spectrum) if we see it from outer space or high-altitude airplanes. Our atmosphere scatters shorter to bigger wavelengths color from sunlight when the white light travels through it. During day, it scatters violet and blue colours leaving yellowish sunlight (the reason why sky is blue and sunlight is yellow). During morning and evening, the sun appears reddish because light rays needs to travel longer distance in atmosphere which causes scattering of yellow light too.

9th Science Guide Matter Around Us Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Liquids have
(a) definite volume, definite shape and are not compressible.
(b) definite volume, no definite shape and are highly compressible.
(c) no definite volume, no definite shape, and slightly compressible
Answer:
(b) definite volume, no definite shape, and slightly compressible

Question 2.
Intermolecular space is maximum in
(a) solids
(b) liquids
(c) gases
(d) all the above
Answer:
(c) gases

Question 3.
Air is a/an,
(a) compound
(b) element
(c) Mixture
(d) Molecule
Answer:
(c) Mixture

Question 4.
Which statement is not correct for a mixture
(a) Components retain their properties
(b) Properties of a mixture are different from its components
(c) Components are mixed in any ratio
(d) Components are separated using simple methods
Answer:
(b) Properties of a mixture are different from its components

Question 5.
A homogeneous mixture of two or more substances is called
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) None of the above.
Answer:
(a) True solution

Question 6.
A colloidal solution is a
(a) Homogeneous mixture
(b) Heterogeneous mixture in which dissolved particles cannot be seen with naked eyes
(c) Heterogeneous mixture in which dissolved particles can be seen with naked eyes
(d) All the above
Answer:
(b) Heterogeneous mixture in which dissolved particles cannot be seen with naked eyes

Question 7.
Muddy water is an example of
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) No solution
Answer:
(b) Suspension

Question 8.
The solution of soap in water is
(a) True solution
(b) Suspension
(c) Colloidal solution
(d) No solution
Answer:
(c) Colloidal solution

Question 9.
Water is a/an
(a) element
(b) Mixture
(c) Molecule
(d) compound
Answer:
(d) compound

Question 10.
When two or more elements combine together they form
(a) element
(b) compound
(c) Mixture
(d) Molecule
Answer:
(b) compound

Question 11.
Which of the following will show the “Tyndall Effect”?
(a) Salt solution
(b) Milk & starch solution
(c) Copper sulphate solution
(d) Sugar solution
Answer:
(b) Milk & starch solution

Question 12.
Solid is an arrangement of particles
(a) close together
(b) far together
(c) far apart
(d) none of these
Answer:
(a) close together

Question 13.
The movement of particles in liquids is …………………..
(a) Vibrate on the spot
(b) around each other
(c) Move quicks in all direction
(d) none of these
Answer:
(b) around each other

Question 14.
Gases change to liquid by the process of . …………………..
(a) Melting
(b) Vapourising
(c) Condensing
(d) Freezing
Answer:
(c) Condensing

Question 15.
The physical state of water at 373 K is …………………..
(a) solid
(b) liquid
(c) vapour
(d) plasma
Answer:
(c) vapour

Question 16.
The constituents that form a mixture are also called …………………..
(a) Elements
(b) Compounds
(c) Alloys
(d) Components
Answer:
(d) Components

II. True or False? If false, correct the statement:

1. Atoms are the tiny particles which repel each other when they are squeezed very close.
Answer:
True

2. A teabag placed in a cup of hot water will diffuse into the water.
Answer:
True

3. Evaporation does form bubbles.
Answer:
False
Correct statement: No does not, only boiling forms bubbles.

4. The energy for the process of sublimation can be derived either from the surroundings or from the heat supplied.
Answer:
True

5. The pressure of gases does not depend on the temperature of the gas and the volume it occupies
Answer:
False
Correct statement: The pressure of gases does depend on the temperature of the gas and the volume it occupies

6. Higher the temperature, higher the kinetic energy of particles.
Answer:
True

7. Solids do not flow.
Answer:
True

8. Gases do not diffuse very easily.
Answer:
False.
Correct statement: Gases diffuse very easily.

9. Mixtures are impure substances.
Answer:
True.

10. Salt solution is an example of a heterogeneous mixture.
Answer:
False.
Correct statement: The salt solution is an example of a homogeneous mixture.

III. Match the following :

1. (i)

Column A	Column B
1. Metal	(a) can be compressed easily
2. Metalloid	(b) have the least density
3.Heating curve	(c) Copper, Mercury, Gold, Chromium
4. Gases	(d) Boron, Germanium, Silicon, Arsenic
5. Liquids	(e) a plot of temperature versus time

Answer:
1) – c, 2) – d, 3) – e, 4) – a, 5) – b

(ii)

Column A	Column B
1. Colloidal solution	(a) Carbon, Oxygen, Chlorine, Neon
2. Homogeneous	(b) C12H22O11
3. Cane sugar	(c) dispersed phase, dispersed medium
4. Non-Metals	(d) Oil shaken in the water
5. Suspensions	(e) True solutions

Answer:
1) – c, 2) – e, 3) – b, 4) – a, 5) – d

2. Match the following.

Dispersed phase & Medium	Examples
1. Solid solid	(a) gel
2. Liquid solid	(b) emulsion
3. Liquid-liquid	(c) solid foam
4. Gas solid	(d)alloys

Answer:
1 – d, 2 – a, 3 – b, 4 – c.

3. Match the following.

Dispersed phase & Medium	Examples
1. Solid-liquid	(a) Aerosol
2. Solid gas	(b) Foam
3. Liquid gas	(c) Sol
4. Gas-liquid	(d) Aerosol

Answer:
1 – c, 2 – a, 3 – d, 4 – b.

IV. Fill in the blanks :

1. A substance must absorb …………….. so that it can melt.
Answer:
heat energy

2. Boiling refers to the process by which a substance changes from the liquid to the gaseous state at its …………. point.
Answer:
boiling

3. ………………… is used for industrial refrigeration and transporting frozen food.
Answer:
Dry ice

4. ……………….. is the SI unit of temperature
Answer:
Kelvin

5. Elements contain the …………………of the same kind
Answer:
atoms

6. When elements are physically mixed they form…………………
Answer:
mixtures

7. A compound has a definite …………………
Answer:
formula

8. Mixture of iron filings and salt is a …………………type of mixtures.
Answer:
heterogeneous

9. …………………is the major difference between true solutions, suspensions and colloids.
Answer:
Particle size

10. Phenomenon of Evaporation takes place at the …………………of a liquid.
Answer:
Surface

11. Inverse of sublimation is called …………………
Answer:
deposition

12. Expand LPG …………………
Answer:
Liquefied Petroleum Gas

13. LPG is ………………… gas.
Answer:
inflammable hydrocarbon

14. Compressibility of solids: …………………..
Answer:
can’t be compressed

15. Fluidity of solids: …………….
Answer:
do not flow

16. A mixture does not have fixed …………………….
Answer:
boiling point (or) melting point

17. A compound has a fixed ………………….
Answer:
boiling point (or) melting point

18. The mixture of Iron filling and sale is …………………
Answer:
heterogeneous

19. Gas-solid is ……………………
Answer:
Solid foam

20. Examples of foam is ……………
Answer:
Soap lather / Aerated water

21. Evaporation is always accompanied by…………..in temperature.
Answer:
decrease / cooling effect

V. Very short answer:

Question 1.
Define ‘matter’.
Answer:
The matter is anything that has mass & occupies space.

Question 2.
What are the three states of matter?
Answer:
Solids, liquids, and gases are the three states of matter.

Question 3.
What is an atom?
Answer:
The smallest unit of an element which may or may not have an independent existence but always take part in a chemical reaction is called an atom.

Question 4.
What is a molecule?
Answer:
The smallest unit of a pure substance which always exist independently and can retain physical and chemical properties of that substance is called a molecule.

Question 5.
Give an example for a molecule.
Answer:
Hydrogen molecule – consists of 2 atoms of hydrogens.

Question 6.
How is matter classified?
Answer:
Matter is classified as pure and impure substances.

Question 7.
How are pure substances classified?
Answer:
Pure substances are classified as elements and compounds.

Question 8.
Give examples of pure substances.
Answer:
Copper, oxygen, hydrogen.

Question 9.
How are impure substances classified?
Answer:
Impure substances are classified as homogeneous and heterogeneous.

Question 10.
How are elements classified?
Answer:
Elements are classified as metals, non-metals, and metalloids.

Question 11.
Give examples for metalloids.
Answer:
Boron, silicon, germanium, and arsenic.

Question 12.
Give the chemical formula for cane sugar.
Answer:
C₁₂H₂₂O₁₁

Question 13.
Expand LPG.
Answer:
Liquefied petroleum gas.

Question 14.
Name the element which is used in toothpaste to strengthen our teeth.
Answer:
Fluorine.

Question 15.
Name the compounds used in fertilizers.
Answer:
Compounds of phosphorus, nitrogen, and potassium are used in fertilizers.

Question 16.
Is blood a pure substance?
Answer:
No blood is not a pure substance. It is a mixture of components such as platelets, red and white blood corpuscles, and plasma.

Question 17.
Name the two types of mixtures.
Answer:
Homogeneous and heterogeneous.

Question 18.
Name some substances that sublime.
Answer:
Camphor, Naphthalene, Mothballs.

Question 19.
Name a suitable method used to separate two immiscible liquids.
Answer:
Separating funnel.

Question 20.
Name a method used to separate two miscible liquids.
Answer:
Fractional distillation.

Question 21.
Name the machine used in the centrifugation process.
Answer:
Centrifuge.

Question 22.
Give an example for liquid in gas.
Answer:
Aerosol.

Question 23.
What is “Brownian motion”?
Answer:
The erratic random movement of microscopic particles in a fluid, as a result of ‘ continuous bombardment from molecules of the surrounding medium was discovered by the scientist Robert Brown and so the movement is called “Brownian motion”

VI. Short answer :

Question 1.
What is an element? ’
Answer:
Each element is made up of only one kind of atom. Element is the building block of all materials. The element of any substance cannot be broken down further into simple substances.

Question 2.
What is a compound?
Answer:
When 2 or more elements combine chemically to form a new substance, the new ‘ substance is called a compound.
Example: H₂O.

Question 3.
What is a mixture?
Answer:
A mixture is an impure substance which contains 2 or more kinds of elements or ‘ compounds or both physically mixed together in any ratio.

Question 4.
What is LPG?
Answer:
LPG is liquefied petroleum gas. It contains a mixture of butane and propane gas.

Question 5.
Distinguish an element and a compound.
Answer:
Element:

1. Made up of only one kind of atom.
2. The smallest particle that retains all its properties in the atom cannot be broken down into simpler substances.

Compound:

1. Made up of more than one kind of atom.
2. The smallest particle that retains all the properties in the molecule can be broken down into elements by chemical methods.

Question 6.
Define sublimation.
Answer:
Certain solid substances when heated change directly from solid to gaseous state without attaining liquid state. The vapours when cooled give back the solid substance. This process is known as sublimation.

Question 7.
What is centrifugation?
Answer:
Centrifugation is the process by which fine insoluble solids from a solid liquid mixture can be separated in a machine called a centrifuge.

Question 8.
What is solvent extraction?
Answer:
Solvent extraction method is used to separate two immiscible liquids. This method works on the principle of difference in solubility of two immiscible liquids in a suitable solvent.

Question 9.
What is distillation?
Answer:
Distillation is the process of obtaining pure liquid from a solution. It is actually a combination of evaporation and condensation.

Question 10.
What is fractional distillation?
Answer:
Fractional distillation is used to separate two or more miscible liquids that do not differ much in their boiling points, (less than 25K).

Question 11.
What is chromatography?
Answer:
Chromatography is a separation technique. It is used to separate different components of a mixture based on their different solubilities in the same solvent.

Question 12.
What is paper chromatography?
Answer:
Paper chromatography is used .to separate the different coloured dyes in a sample. It is based on the principle of different solubility in the solvent which is absorbed to different extents by the chromatography paper.

Question 13.
What is a solution?
Answer:
A solution is a homogeneous mixture of two or more substances.

Question 14.
What is a solute?
Answer:
In a solution, the component present in a lesser amount by weight is solute.

Question 15.
What is the solvent?
Answer:
In a solution, the component present in a larger amount by weight is solvent.

Question 16.
What are Colloidal Solutions?
Answer:
A colloidal solution is a heterogeneous system consisting of the dispersed phase and the
dispersion medium.

Dispersed phase

1. Component present in smaller proportion
2. Analogous to solute of a true solution

Dispersion medium

1. Component present in larger proportion
2. Analogous to solvent of a true solution

Question 17.
What is Tyndall effect?
Answer:
Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution the path of the beam becomes visible. This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone. This phenomenon is not observed in case of true solution.

Question 18.
What are the Types of emulsions?
Answer:
The two liquids mixed can form different types of emulsions. For example, oil and water can form an oil in water emulsion, where the oil droplets are dispersed in water, or they can form a water in oil emulsion, with water dispersed in oil.

Question 19.
What are the uses of emulsions?
Answer:
Emulsions find wide applications in food processing, pharmaceuticals, metallurgy, and many other important industries.

VII. Answer in detail :

Question 1.
What are the characteristics of Pure Substances? (or) List out the characteristics of Pure Substances.
Answer:

• Made up of only one kind of atom or molecule.
• The ratio of the components of a pure substance is fixed.
• Have a characteristic set of properties. Physical properties like boiling point, melting point, density etc. are
• fixed. Such properties will vary with the proportions of constituents present in the mixture.
• Has the same composition throughout i.e it is homogenous in nature

Question 2.
List out the characteristics of Mixtures.
Answer:

• The constituents of a mixture are loosely held together without any chemical force between the constituents and in such a case the constituents retain their individual properties.
• A mixture can be prepared by mixing the constituents in any proportion i.e mixtures do not have any fixed amount of constituents Formation of mixtures does not involve any exchange of energy.
• Mixtures do not have any characteristic set of properties. Physical properties of mixtures like boiling point, melting point, etc. are not fixed. Such properties will vary with the proportions of constituents present in the mixture.
• Components of a mixture can be separated by physical methods.

Question 3.
Tabulate Differences between mixtures and compounds.
Answer:
Mixtures

1. A mixture can be separated into its constituents by physical processes like filtration, evaporation, sublimation, magnet distillation, solvent extraction.
2. A mixture retains or shows the properties of its constituents
3. Energy (in the form of heat light etc.) is neither given out nor absorbed in the preparation of a mixture
4. The composition or proportion is variable a mixture does not have a definite formula
5. A mixture does not have a fixed boiling point or melting point

Compounds :

1. A compound cannot be separated into its constituents by physical processes but can be only separated by a chemical process
2. The properties of a compound are entirely different from those of its constituent elements
3. Energy (in the forth of heat, light etc.) is given out or absorbed during the preparation of a compound
4. The composition of a compound is fixed. The constituents are present in a fixed ratio by mass. The compound has a definite formula.
5. A compound has a fixed boiling point or melting point

Question 4.
Write the Classification of colloids based on physical state of dispersed phase and dispersion medium.
Answer:
Dispersed phase or the dispersion medium can be a solid, or liquid or gas. There are eight different combinations possible (The combination in which both the dispersed phase and dispersion medium are gases does not exist as gases are completely miscible and can never give rise to a colloidal solution).

Question 5.
Two immiscible liquids are taken in the above funnel for separation.
Which is denser, X or Y? Suggest any one example for X and one for Y. A third liquid Z which is soluble only in Y is added to the mixture and contents in the funnel are shaken well. How many layers will you observe now? How will you separate the three liquids? Boiling point of X is 98°C, that of Y is 43°C and that of Z is 75°C.
Answer:
Boiling point of the 3 liquids are given as
X is 98°C – Which corresponds to water.
Y is 43°C – Which corresponds to oil.
Z is 75°C – Which corresponds to alcohol.
‘Y’ is more denser.
Only two layers are observed. X is separated by separating funnel, Z is separated by distillation method. Y – is in the distillation flask.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 12 Periodic Classification of Elements Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Chapter 12 Periodic Classification of Elements

9th Science Guide Periodic Classification of Elements Text Book Back Questions and Answers

I. Choose the correct answer :
Question 1.
If Dobereiner is related with ‘law of triads’, then Newlands is related with
(a) Modem periodic law
(b) Hund’s rule
(c) Law of octaves
(d) Pauli’s Exclusion principle
Answer:
(c) law of octaves

Question 2.
Modern periodic law states that the physical and chemical properties of elements are the periodic functions of their ……………
(a) atomic numbers
(b) atomic masses
(c) similarities
(d) anomalies
Answer:
(a) atomic numbers

Question 3.
Elements in the modern periodic table are arranged in …………. groups and ………….. periods .
(a) 7, 18
(b) 18,7
(c) 17,8
(d) 8, 17
Answer:
(b) 18, 7

Fill in the blanks:

1. In Dobereiner’s triads, the atomic weight of the middle element is the __________ of the atomic masses of 1 and 3rd elements.
Answer:
average

2. Noble gases belong to ___________ group of the periodic table.
Answer:
18th

3. The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was ……………….
Answer:
atomic mass

4. Example for liquid metal is ______________ .
Answer:
mercury

III. Match the following:
Question

Triads	Newlands
Alkali metal	Calcium
Law of octaves	Henry Moseley
Alkaline earth metal	Sodium
Modern Periodic Law	Dobereiner

Answer:

Triads	Dobereiner
Alkali metal	Sodium
Law of octaves	Newlands
Alkaline earth metal	Calcium
Modern Periodic Law	Henry Moseley

IV. State whether true or false. If false, correct the statement:

Question 1.
Newlands’ periodic table is based on atomic masses of elements and modem periodic table is based on atomic number of elements.
Answer:
True.

Question 2.
Metals can gain electrons.
Answer:
False.
Correct statement: Metals tend to lose electrons.

Question 3.
Alloys bear the characteristics of both metals and nonmetals.
Answer:
False.
Correct statement: Metalloids bear the characteristics of both metals and nonmetals.

Question 4.
Lanthanides and actinides are kept at the bottom of the periodic table because they resemble each other but they do not resemble with any other group elements.
Answer:
True.

Question 5.
Group 17 elements are named as Halogens.
Answer:
True.

V. Assertion and Reason :

Question
Statement : Elements in a group generally possess similar properties but elements along a period have different properties.
Reason : The difference in electronic configuration makes the element differ in their chemical properties along a period.
a) Statement is true and reason explains the statement.
b) Statement is false but the reason is correct.
Answer:
(a) Statement is true and reason explains the statement

VI. Answer the following :

Question 1.
State modern periodic law.
Answer:
The modem periodic law states that:
“The Chemical and Physical properties of elements are periodic functions of their atomic numbers”.

Question 2.
What are groups and periods in the modern periodic table?
Answer:

•  The horizontal rows in the periodic table are called periods.
• Vertical columns in the periodic table starting from top to bottom are called groups.

Question 3.
What are the limitations of Mendeleev’s periodic table?
Answer:

• Elements with large differences in properties were included in the same group. Eg: Hard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium (Na) and potassium (K).
• No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), sodium (Na) and potassium (K).
• The increasing order of atomic mass was not strictly followed throughout. Eg. Co & Ni, Te &I.
• No place for isotopes in the periodic table.

Question 4.
State any five features of the modern periodic table.
Answer:

• All the elements are arranged in the increasing order of their atomic number.
• The horizontal rows are called periods. There are seven periods in the periodic table.
• The elements are placed in periods based on the number of shells in their atoms.
• Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
• Based on the physical and chemical properties of elements, they are grouped into various families.

Intext Activities

ACTIVITY -1

Find the pair of elements having similar properties by applying Newlands’ law of Octaves
(Example: Mg & Ca):
Set I : F, Mg, C, O,B
Set II: Al, Si, S, Cl, Ca
Answer:

1. F-Cl
2. Mg-Ca
3. C-Si
4. O-S
5. B-Al

9th Science Guide Periodic Classification of Elements Additional Important Questions and Answers

Choose the correct answer:

Question 1.
Noble gases are placed in the _______ group in the modern periodic table.
(a) 13th
(b) 18th
(c) 17th
(d) 2nd
Answer:
(b) l8th

Question 2.
Group 16 elements are collectively called as _______ .
(a) chalcogen family
(b) carbon family
(e) halogens
(d) nitrogen family
Answer:
(a) chalcogen family

Question 3.
The maximum number of electrons that can be accommodated in s, p ,d, and f subshells are _________ .
(a) 14, 10, 6, 2
(b) 6, 10, 2, 14
(c) 2, 6, 10, 14
(d) 6, 2, 14, 10
Answer:
c) 2, 6, 10, 14

Question 4.
d-block elements are otherwise known as _________ .
(a) transition elements
(b) inner transition elements
(c) halogens
(d) alkali metals
Answer:
(a) transition elements

Question 5.
Which block of the periodic table contains metals, non-metals and metalloids?
(a) s
(b) p
(c) d
(d) f
Answer:
(b) p

Question 6.
Which of the following non-metals can form alloys with metals?
(a) Boron
(b) Carbon
(c) Silicon
(d) All the above
Answer:
(d) all the above

Question 7.
Which of the following metals have low melting and boiling point?
(a) Sodium :
(b) Potassium
(e) Iroñ
(d) Both a & b
Answer:
(d) Both a & b

Question 8.
Which of the following metal (s) do not react with water?
(a) Gold
(b) Silver
(c) Copper
(d) All the above
Answer:
(d) All the above

Question 9.
If the electronic configuration of an element is 1s² 2s² 2p⁶ 3s² 3p¹’then it will
occupy ……………… block of the periodic table.
(a) s
(b) p
(c) d
(d) f
Answer:
(b) p

II. Fill in the blanks :

1. ……………… group elements are called alkaline earth metals.
Answer:
Second

2. The elements that follow lanthanum are called ……………..
Answer:
Lanthanides

3. f-block elements are also known as …………………..
Answer:
inner transition elements

4. …………… block element is placed at the bottom of the periodic table.
Answer:
f-

5. The mixture of metal with mercury is called …………………..
Answer:
amalgam

6. Elements are placed in periods based on the number of ……………… in their atoms.
Answer:
shells

III. Spot the error :

Question 1.
The elements of group 13 are called the carbon family.
Answer:
The elements of group 13 are called boron family
(or)
The elements of group 14 are called the carbon family.

Question 2.
There are 5 periods and 17 groups in the modern periodic table.
Answer:
There are 7 periods and 18 groups in the modem periodic table.

IV. Pick the odd one out and write the reason:

Question 1.
Copper, brass, gold ornament, bronze.
Answer:
Copper.
Copper is metal whereas the other three are alloys.

Question 2.
Bromine, carbon, hydrogen, aluminium.
Answer:
Aluminium.
Aluminium is metal whereas the other three are non-metals.

V. To match :

Group in the modern periodic table	Families
a) 1	?
b) ?	Transition metals
c) ?	Boron family
d) 15	?
e) 17	?

Answer:
a) alkali metals
b) 3 to 12
c) 13
d) Nitrogen family
e) halogens

VI. Answer in brief :

Question 1.
What are the s-block elements?
Answer:
Elements whose valence electron is filled in s subshell is known as s-block elements.

Question 2.
What are the p-block elements?
Answer:
The last electron in these elements is filled in p subshells and hence these elements are called p block elements. These elements are in group 13 to 18 in the periodic table.

Question 3.
What are alloys?
Answer:
Alloys are mixtures of two or more metals and are formed by mixing molten metals thoroughly. Rarely nonmetals are also mixed with metals to produce alloys.

Question 4.
What are metalloids? Give examples.
Answer:
Elements which have the properties of both metals and non-metals are called as metalloids, (eg) Boron, Arsenic.

Question 5.
State Mendeleev’s Law of Periodicity.
Answer:
The physical and chemical properties of elements are the periodic functions of their atomic masses.

Question 6.
State Newlands’ Law of Octaves.
Answer:
Every eighth element had properties similar to those of the first element like the eighth note in an octave of music is similar to the first.

Question 7.
An element has atomic number 12.
a) Write the electric configuration.
b)To which group and period do it belong.
Answer:
a) K = 2, L = 8, M = 2
b) Group No . 2, Period No. 3

Question 8.
Relate the names of the following scientists with the statements given below. (Mendeleev, Newlands, Dobereiner).
a) Arranged elements into groups containing three elements each.
b) Arranged elements in a group of seven with increasing atomic masses and eighth elements with similar properties kept below the first like eight note in an act of music.
c) Arranged elements in the increasing order of atomic mass
Answer:
a) Dobereiner
b) Newlands
c) Mendeleev

Question 9.
Complete the following triads by inserting the missing elements.
a) Cl, ………., I
b) Li, ………, K
c) Ca, …………, Ba
Answer:
a) Br
b) Na
c) Sr

Question 10.
How are elements grouped into various families in the periodic table?
Answer:
Based on the physical and chemical properties of elements, they are grouped into various families.

VII. To interpret:

Question 1.
Group 1 (except hydrogen) elements are called alkali metals.
Answer:
The elements of group 1 (except hydrogen) are metals. They react with water to form solutions that change the colour of a vegetable dye from red to blue. These solutions are said to be highly alkaline or basic. Hence they are called alkali metals.

Question 2.
d-block elements are called transition elements.
Answer:
d-block elements are found in the centre of the periodic table. Their properties are intermediate to that of s block and p block elements and so they are called transition elements.

Question 3.
Group 3-12 elements in the modern periodic table are called d block elements.
Answer:
The elements of group 3 to 12 have their valence electrons in their outermost d subshells. These elements are called d block elements.

VIII. Complete the following table :

Question

Symbol	Atomic No.	Electronic Configuration
1) He	2	?
2) Ne	?	2,8
3) Ar	?	2, 8,8
4) Na	11	?

Answer:
1) 2
2) 10
3) 18
4) 2,8,1

IX. Assertion and Reason :

Question 1.
Assertion (A): Group 2 elements in the modem periodic table are called alkaline earth metals.
Reason (R): The oxides of group 2 elements produce alkaline solutions when they are dissolved in water.
(a) A is right R is wrong
(b) R explains A
(c) R does not explain A
(d) R is right A is wrong
Answer:
(b) R explains A

Question 2.
(A) : Noble gases are chemically inert in nature.
Reason (R) : Noble gases have stable electronic structures.
(a) Both A & R are right
(b) Both A & R are wrong
(c) A is right R is wrong
(d) A is wrong R is right
Answer:
(a) Both A & R are right]

Question 3.
Assertion (A): Non-metals are electronegative.
Reason (R) : Non-metal losë electrons to form cation.
(a) Both A & R are right
(b) Both A & R are wrong
(c) A is right R is wrong
(d) A is the wrong R is right
Answer:
(c) A is right R is wrong

X. Long answer type questions:

Question 1.
List the advantages of alloys.
Answer:

• Alloys do not get corroded or get corroded to a very less extent.
• They are harder and str9ner than pure metals (Example: Gold is mixed with copper and it is harder than pure gold)
• They have less conductance than pure metals (Example: Copper is a good conductor of heat and electricity whereas brass and bronze are not good conductors)
• Some alloys have lower melting point than pure metals (Example: Solder is an alloy of lead and tin which has a lower melting point thàn each of the metals)
• When metal is alloyed with mercury, it is called amalgam.

Question 2.
Write the advantages of the Modern Periodic Table.
Answer:

• The table is based on a more fundamental property i.e., atomic number.
• It correlates the position of the element with its electronic configuration more clearly.
• The completion of each peçiod is more logical. In a period, as the atomic number increases, the energy shells are gradually filled up until an inert gas configuration is reached.
• It is easy to remember and reproduce.
• Each group is an independent group and the idea of subgroups has been discarded.
• One position for all isotopes of an element is justified since the isotopes have the same atomic number.
• The position of the eighth group (in Mendeleev’s table) is also justified in this table. All transition elements have been brought in the middle as the properties of transition elements are intermediate between the left portion and right portion elements of the periodic table.
• The table completely separates metals from nonmetals. The nonmetals are present in the upper right corners of the periodic table.
• The positions of certain elements which were earlier misfit (interchanged) in Mendeleev’s periodic table are now justified because it is based on an atomic number of the elements.
• Justification has been offered for placing lanthanides and actinides at the bottom of the periodic table.

Question 3.
Explain the position of hydrogen in the periodic table.
Answer:
Hydrogen is the lightest, smallest and first element of the periodic table. Its electronic configuration (1s¹) is the simplest of all the elements. It occupies a unique position in the periodic table. It behaves like alkali metals as well as halogens in its properties. In the periodic table, it is placed at the top of the alkali metals.

• Hydrogen can lose its one electron to form a hydrogen ion (H⁺) like alkali metals.
• It can also gain one electron to form the hydride ion (H^–) like halogens.
• Alkali metals are solids while hydrogen is a gas.
  Hence the position of hydrogen in the modem periodic table is still under debate
  as the properties of hydrogen are unique.

Question 4.
List the features of Mendeleev’s Periodic Table.
Answer:
1. It has eight vertical columns called ‘groups’ and seven horizontal rows called ‘period’.

2. Each group has two subgroups ‘A’ and ‘B’. All the elements appearing in a group were found to have similar properties.

3. For the first time,-elements were comprehensively classified in such a way that elements of similar properties were placed in the same group.

4. It was noticed that certain elements could not be placed in their proper groups in this manner. The reason for this was wrongly determined atomic masses, and consequently those wrong atomic masses were corrected. Eg: The atomic mass of beryllium was known to be 14. Mendeleev reassessed it as 9 and assigned beryllium a proper place;

5. Columns were left vacant for elements which were not known at that time and their properties also were predicted. This gave me the motivation to experiment in Chemistry. Eg: Mendeleev gave the names Eka Aluminium and Eka Silicon to those elements which were to be placed below aluminium and silicon respectively in the periodic table and predicted their properties. The discovery of Germanium later on, during his lifetime, proved him correct.

Properties of Germanium:

Property	Mendeleev’s prediction (1871)	Actual property (1886)
Atomic Mass	About 72	72.59
Specific Gravity	5.5	5.47
Colour	Dark grey	Dark grey
Formula of oxide	EsO2	GeO2
Nature of chloride	ESCl4	GeCl4

 

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 8 Sound Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 8 Sound

9th Science Guide Sound Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following vibrates when a musical note is produced by the cymbals in a orchestra?
(a) stretched strings
(b) stretched membranes
(c) air columns
(d) metal plates
Answer:
(d) metal plates

Question 2.
Sound travels in air:
(a) if there is no moisture in the atmosphere.
(b) if particles of medium travel from one place to another.
(c) if both particles as well as disturbance move from one place to another.
(d) if disturbance moves.
Answer:
(d) if disturbance moves

Question 3.
A musical instrument is producing continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through
(a) wax
(b) vacuum
(c) water
(d) empty vessel
Answer:
(b) vacuum

Question 4.
The maximum speed of vibrations which produces audible sound will be in
(a) seawater
(b) ground glass
(c) dry air
(d) Human blood
Answer:
(b) ground glass

Question 5.
The sound waves travel faster
(a) in liquids
(b) in gases
(c) in solids
(d) in vacuum
Answer:
(c) in solids

II. Fill in the blanks.

1. Sound is a ……………….wave and needs a material medium to travel.
Answer:
longitudinal mechanical

2. Number of vibrations produced in one second is………………..
Answer:
Frequency

3. The velocity of sound in solid is …………… than the velocity of sound in air.
Answer:
greater

4. Vibration of object produces ……………..
Answer:
Sound

5. Loudness is proportional to the square of the ……………………
Answer:
Amplitude of vibration of sound

6. …………..is a medical instrument used for listening to sounds produced in the body.
Answer:
Stethoscope

7. The repeated reflection that results in persistence of sound is called ……………………
Answer:
Reverberation

III. Match the following :

1. Tuning fork	a. The point where density of air is maximum.
2. Sound	b. Maximum displacement from the equilibrium position.
3. Compressions	c. The sound whose frequency is greater than 20,000 Hz
4. Amplitude	d. Longitudinal wave
5. Ultrasonics	e. Production of sound

Answer:
1 – e, 2 – d, 3 – a, 4 – b, 5 – c

IV. Answer in brief :

Question 1.
Through which medium sound travels faster, iron or water? Give reason.
Answer:
Sound travels faster through iron than water.
Reason: The speed of sound depends on the nature of the medium. As Iron is a solid, sound travels faster through iron than Water.

Question 2.
Name the physical quantity whose SI unit is ‘hertz’. Define.
Answer:
The SI unit of frequency is Hertz. Frequency is the number of waves produced in one second.

Question 3.
What is meant by supersonic speed?
Answer:
Supersonic speed is the speed of an object that exceeds the speed of sound in air (330 ms^-1).

Question 4.
How does the sound produced by a vibrating object in a medium reach your ears?
Answer:

• When an object vibrates, it sets the particles of the medium around it vibrating.
• The vibrating particles in the medium displace from the equilibrium position and exerts pressure on adjacent particles.
• Thus this process continues in the medium till the sound reaches our ear.

Question 5.
You and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
We cannot hear any sound on the moon.
Reason: Absence of atmosphere (medium) in the moon.

V. Answer in detail :

Question 1.
Describe with a diagram, how compressions and rarefactions are produced.
Answer:
Compressions :
When a vibrating body moves forward, it creates a region of high pressure is known as compressions. In compression, the particles are denser. Compressions are the region where particles are crowded together.

Rarefaction :
When the vibrating body moves backward, it creates a region of low pressure (i.e) low density of particles. This is called rarefaction. Rarefactions are the regions where particles are spread apart.

Question 2.
Verify experimentally the reflection of the laws of sound.
Answer:

• Make two identical long pipes using chart paper.
• Arrange them on a table near wall.
• Keep a clock near the open end of one pipe and hear the sound of the clock through the other pipe.
• Adjust the pipe till the sound of the clock heard with more clarity.
• Now measure the angle of incidence and reflection and see the relationship between the angles.
• The angle in which the sound is incident is equal to the angle in which sound is reflected.
• Direction of incident sound, direction of the reflected and the normal are in the same plane.
• Thus laws of reflection of sound are verified.

Question 3.
List the applications of sound.
Answer:
Applications of ultrasound

• Ultrasound can be used in cleaning technology. Minute foreign particles can be removed from objects placed in a liquid bath through which ultrasound is passed.
• Ultrasounds can also be use d to detect cracks and flaws in metal blocks.
• Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.
• Ultrasound may be employed to break small ‘stones’ formed in the kidney into fine grains. These grains later get flushed out with urine.

Question 4.
Explain how do SONAR works?
Answer:
SONAR stands for Sound Navigation And Ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction, and speed of underwater objects. Sonar consists of Science – 9 (Physics)
a transmitter and a detector and is installed at the bottom of boats and ships. The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector.

The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. Sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarines, icebergs etc.

VI. Numerical problems :

Question 1.
The frequency of a source of sound is 600 Hz. Calculate the number of times it vibrates in a minute?
Solution :
Given :
Frequency, v = 600 Hz.
Frequency = Number of vibrations in a second.
Frequency in a minute = Fequency per second × 60
= 600 Hz × 60
No. of vibrations in a minute = 36,000 Hz (or) 36 kHz.

Question 2,.
A stone is dropped from the top of a tower 750 m high into a pond of water at the base of the tower. Calculate the number of seconds for the splash to be heard? (Given g = 10 ms^-2 and speed of sound = 340 m s^-1)
Solution :
Given :
Height of tower, s = 750 m
Acceleration, g =10 ms^-2
Speed of sound, v – 340 ms^-1
Initial velocity of stone, u =0 (stone at rest)

Consider
(i) Time taken to reach the pond, t₁
(ii) Time taken by sound to reach top, t₂
According to Equation of Motion, s = ut + \(\frac{1}{2}\) at²
Here, s = ut₁ + \(\frac{1}{2}\) gt₁²
Substituting the values, 750 = 0 × t₁ + \(\frac{1}{2}\) × 10 × t₁²
750 = 5 t₁²
t₁² = 150
t₁ = 12.25 s
Time taken by sound to reach top t₂ = \(\frac{s}{v}=\frac{750}{340}\) = 2.2s
t₂ = 2.2 s
Time for splash to be heard at top, t = t₁ + t₂
t = 12.25 + 2.2
t = 14.45 s
Time for splash to be heard at top, t = 14.45 s.

Intext Activities

ACTIVITY – 1

Take a tuning fork and strike its prongs on a rubber pad. Bring it near your ear. Do you hear any sound? Now touch the tuning fork with your finger. What do you feel? Do you feel vibrations?

Aim :
To demonstrate the vibration of a molecule.
Materials Required : 1. Tuning fork, 2. Rubber band.

Procedure:

1. Take a tuning fork and strike its prongs on a rubber pad.
2. Bring it near your ear. Hear the sound.
3. Touch the tuning fork with finger.
4. Try to feel the vibrations.

Observation :
When we strike the tuning fork on the rubber pad, it starts vibrating. The vibrations can be felt.

Conclusion :
The tuning fork vibrates the molecules which will vibrate the nearby molecules.
[Vibration = movement of molecule from mean position],

[End of the activity]

ACTIVITY – 2

Take a coil or spring and move it forward and backward. What do you observe? You can observe that in some parts of the coil the turns will be closer and m some other parts the turns will be far apart.
Sound also travels in a medium in the same manner. We will study this now.

Aim :
To demonstrate the propagation of Longitudinal wave. (Sound)
Materials required : 1. Coil, 2. Spring

Procedure:

1. Take a coil or spring
2. Move it forward and backward.

Observations:

1. Some parts of the coil, the turns are closer.
2. In other parts, the turns are far apart.

Conclusion :

1. Closer turns represent compressions.
2. Far apart turns are rarefactions.
3. Longitudinal waves propagate through compressions and rarefactions.

[End of the activity]

ACTIVITY – 3

Listen to the audio of any musical instruments like flute, nathaswaram, tabla, drums, veena etc., Tabulate the differences between the sounds produced by the various sources.

Aim :
To compare the sounds of musical instruments.
Materials required: 1. Flute, 2. Drums, 3. Veena,

Procedure :

1. Hear the instrumental music of flute, drums and veena.
2. Tabulate the difference between the sounds.

Observation :

Name of musical instrument	Vibrating Part	Characteristics
1. Flute	Air column	Longer wavelength, low-frequency low pitch.
2. Drums	Stretched membrane	Shorter wavelength, high-frequency High pitched
3. Veena	Stretched string

Conclusion :
Sounds in the different music instruments are characterised by the following qualities such as. 1. Amplitude, 2. The wavelength, 3. Frequency, 4. Pitch, 5. Loudness.

9th Science Guide Sound Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Which of the following is a non-mechanical wave?
(a) sound
(b) water
(c) light
(d) none of the above
Answer:
(c) light

Question 2.
Sound cannot travel through …………………
(a) darkness
(b) gases
(b) vacuum
(d) all of these
Answer:
(c) vacuum

Question 3.
In longitudinal waves, the particle vibrates in a ………………….. direction of propagation.
(a) parallel
(b) perpendicular
(c) curved
(d) all of these
Answer:
(b) perpendicular

Question 4.
Human beings cannot hear …………………
(a) infrasonic sound
(b) sonic sound
(c) ultrasonic sound
(d) a & c
Answer:
(d) a & c

Question 5.
The frequency greater than 20,000 Hz is ………………. sound.
(a) infrasonic
(b) ultrasonic
(c) audible
(d) sonic
Answer:
(b) ultrasonic

Question 6.
of sound depends on the amplitude of the wave,
(a) Loudness
(b) Pitch
(c) Timbre
(d) Tone
Answer:
(a) Loudness

Question 7.
………………. is a general term for the distinguishable characteristic of wave
(a) Pitch
(b) Amplitude
(c) Frequency
(d) Timbre
Answer:
(d) Timbre

Question 8.
Sound travels in air as ……………..wave.
(a) longitudinal
(b) transverse
(c) electromagnetic
(d) all of these
Answer:
(a) longitudinal

Question 9.
The distance between two adjacent crest is called …………………..
(a) amplitude
(b) wavelength
(c) time period
(d) frequency
Answer:
(b) wavelength

Question 10.
When temperature increases the speed of sound
(a) increases
(b) decreases
(c) remains same
(d) none of these
Answer:
(a) increases

Question 11.
The relation between speed, frequency and wavelength is ………………


Answer:
(c) V = γλ

Question 12.
SI unit of wavelength is ……………………………..
(a) Hertz
(b) metre per second
(c) decibel
(d) metre
Answer:
(d) metre

Question 13.
The speed of sound in a gaseous medium depends on …………….
(a) pressure
(b) temperature
(c) density
(d) all of these
Answer:
(d) all of these

Question 14.
The elastic property of medium is a factor of …………. medium.
(a) gas
(b) liquid
(c) solid
(d) none of these
Answer:
(c) solid

Question 15.
To hear an echo, the minimum distance of the obstacle from the source of sound must be ………………
(a) 34 m
(b) 17 m
(c) 340 m
(d) 170 m
Answer:
(b) 17 m

Question 16.
The part of ear that turns pressure variations into electrical signals is .
(a) the hammer
(b) anvil
(c) cochlea
(d) stirrup
Answer:
(c) cochlea

Question 17.
The frequency of source of sound is 60 Hz. Then the number of vibrations in a minute will be ………………..
(a) 36
(b) 360
(c) 3600
(d) 6000
Answer:
(c) 3600

Question 18.
Sonar is a device that uses to measure the distance, direction and speed of the underwater objects.
(a) radio waves
(b) infrared waves
(c) water waves
(d) ultrasonic waves
Answer:
(d) ultrasonic waves

Question 19.
The speeds of sound in four different media are given below. Which of the following is the most likely speed in ms-1 with which the two underwater whales in a sea can talk to each other when separated by a large distance?
(a) 5170
(b) 1280
(c) 340
(d) 1530
Answer:
(d) 1530

[Note = Speed of sound in Sea Water is 1530 ms^-1]

II. Fill in the blanks :

1. The propagating disturbance that travels in a medium is called a ………………
Answer:
Wave

2. Rarefactions are the regions of ……………. where particles are spread apart.
Answer:
low pressure

3. Sound travels faster in ……………. and slower in ……………..
Answer:
Solid, Gas

4. The loudness of sound depends on the ……………. of the sound wave.
Answer:
Intensity

5. A sound of single frequency is called …………….and a collection of tones is called .
Answer:
Tone, Note

6. The speed of sound in air at 0°C is ……………..
Answer:
330 ms^-1

7. …………….is an unwanted sound.
Answer:
Noise

8. Loudness equal to (or) greater than …………….can be painful to the ear.
Answer:
120 dB

9. …………….allows bats to navigate through dark caves and find insects for food.
Answer:
Echolocation

10. …………….is an image obtained by the use of reflected ultrasonic waves.
Answer:
An echogram

11. Depth of an ocean can be determined by …………….
Answer:
SONAR

12. The distance of underwater objects can be deduced by the formula …………….
Answer:
Id = v x t

13. …………….muscle contracts in response to electrical depolarisation of the muscle cells.
Answer:
Cardiac

14. Velocity of sound by a tuning fork frequency of 480 Hz is 340 ms Its wavelength is …………….
Answer:
0.7 m

15. The part of ear that collects the sound from the surroundings is . …………….
Answer:
Pinna

16. Ultrasounds can also be used to detect cracks and flaws in …………….
Answer:
Metal blocks

17. In the inner ear, the pressure variations are turned into electrical signals by the …………….
Answer:
Cochlea

III. Match the following :

I.

1. Stethoscope	a) Repeated reflections
2. Echogram	b) Multiple reflections
3. SONAR	c) Ultrasonic waves
4. Reverberation	d) Speed of underwater objects

Answer:
1-b, 2-c,3-d,4-a

II.

1.  Wave	a) Unwanted sound
2. Sound	b) Successive reflections
3. Noise	c) Movement of disturbance
4. Thunder	d) Mechanical wave

Answer:
1-c, 2-d, 3 -a, 4-b

III.

1. Cochlea	a) Amplification of vibrations
2. Pinna	b) Electrical signals to the brain
3. Ear bones	c) Pressure variations to an electrical signal
4. Auditory nerve	d) Collection of sound

Answer:
1-c, 2-d,3 -a,4-b

IV. Assertion and Reason type questions :

Mark the correct choice as :
(a) If both Assertion and Reason are true and Reason is the correct explanation of
Assertion. .
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion : Human beings Cannot hear infrasonic sound.
Reason : Sound with frequency less than 20 Hz is called infrasonic sound.
Answer:
(a) Both Assertion and Reason are true and Reason . is the correct explanation of Assertion

Question 2.
Assertion : As the amplitude of sound increases, the loudness of sound decreases.
Reason : The loudness of sound depends on the amplitude of the wave.
Answer:
(d) Assertion is false but reason is true
Correct Assertion : As the amplitude of sound decreases, the loudness of sound decreases.

Question 3.
Assertion : The sound of thunder is heard a little latter than the flash of light.
Reason : The speed of sound is much less than the speed of light.
Answer:
(a) Both Assertion and reason are true and Reason is the correct explanation of Assertion

Question 4.
Assertion : The speed of sound in air is less than speed of sound in solid.
Reason : If we increase the temperature of medium, the speed of sound increases in any medium.
Answer:
(b) Both assertion and reason are true but reason is not the correct explanation of assertion
Reason : The particles in sound are closer in solids than air.

Question 5.
Assertion : The sound which we hear again is called Echo.
Reason : The sensation of sound (Echo) persists in our brain for about 1 s.
Answer:
(c) Assertion is true but reason is false
Reason : The sensation of sound persists in our brain for about 0 – 1 s.

V. State whether true or false. If false, correct the statement:

1. Vibrating particles travel all the way from vibrating object to ear. ,
Answer:
False.
Correct statement: Vibrating particles do not travel all the way from vibrating object to ear.

2. The small to and fro motion is called vibration.
Answer:
True.

3. Pitch is a general term for the distinguishable characteristic of a tone.
Answer:
false.
Correct statement: Timbre is general term for the distinguishable characteristic of a tone.

4. The speed of sound in a gaseous medium depends on the nature of gas.
Answer:
True.

5. The direction of incident sound, direction of reflected sound and the normal are in different Planes.
Answer:
False.
Correct statement: The direction of incident sound, direction of reflected sound and the normal are in same plane.

6. Ultrasonic sounds cannot be heard by the Human beings.
Answer:
True.

7. The Eardrum moves inward when a rarefaction reaches it.
Answer:
False.
Correct statement: The Eardfum moves outward when a rarefaction reaches it.

VI. Very Short Answer questions :

Question 1.
What is a wave?
Answer:
The disturbance which is carried forward in a medium is called wave.

Question 2.
Distinguish between compression and rarefactions.
Answer:
Compression :
Compressions are the regions where particles are crowded together.

Rarefaction :

Rarefactions are the regions of low pressure where particles are spread apart.

Question 3.
Name the five characteristics of’a sound wave. ‘
Answer:
1. Amplitude, 2. Frequency, 3. Time period, 4. Wavelength, 5. Velocity or speed.

Question 4.
Name the distinguishing factors of sound.
Answer:
1. Loudness, 2. Pitch, 3. Timbre (or) quality.

Question 5.
Define : Intensity.
Answer:
Intensity is defined as the amount of energy per unit time perpendicular to the direction of propagation of the wave.

Question 6.
Differentiate tone from note.
Answer:
Tone : A sound of single frequency
Note : A collection of tones.

Question 7.
What is Reverberation?
Answer:
The repeated reflection that results in persistent sound is called reverberation.

Question 8.
Expand the abbreviation of the term SONAR.
Answer:
SONAR – SOUND NAVIGATION AND RANGING.

Question 9.
What type of waves are illustrated by the movement of a rope whose one end is moved up and down?
Answer:

• The movement of rope whose one end is moved up and down is an example of
  Transverse wave.
• The movement of particles of the medium is perpendicular to the direction of
  propagation of the wave is called Transverse Wave.

Question 10.
Name the type of waves produced when a tuning fork is struck in air.
Answer:
Longitudinal waves are produced when a tuning fork is struck in air.

Question 11.
A stone is dropped on the surface of water in a pond. Name the types of waves produced.
Answer:
Transverse waves are produced when a stone is dropped into the pond.

Question 12.
State one observation from every day life which shows that sound travels much more slower than light.
Answer:
The flash of lightening is seen before we hear the sound of thunderstorm.
Reason : The speed of sound (344 m/s) is less than the speed of light (3 × 10⁸ m/s)

Question 13.
What name is given to those air-crafts which fly at speeds greater than the speed of sound?
Answer:
Supersonic Aircraft.

Question 14.
Name the device which is used to produce sound in laboratory experiments.
Answer:
Tuning fork is used to produce sound in laboratory experiments.

Question 15.
What should an object do to produce sound?
Answer:

• An object should vibrate in a medium.
• Vibrations travel as disturbances to reach our ears as sound.

Question 16.
Can sound travel through vacuum?
Answer:

• Sound cannot travel through vacuum.
• Sound needs a material medium to travel like air, water, steel, etc.

VII. Answer in brief :

Question 1.
How do we hear sound?
Answer:

• Mechanical energy vibrates an object.
• The vibrations reach our ear and we hear sound.

Question 2.
Why are sound waves called mechanical waves?
Answer:
Sound waves are called as mechanical waves because sound waves need a medium to propagate and propagation through medium due to interaction of the particles.

Question 3.
Define : (i) Amplitude (ii) Frequency
Answer:
Amplitude (A) : The maximum displacement of the particles of the medium from their original undisturbed position when a wave passes through the medium. Unit: metre (m).
Frequency (n) : The number of vibrations produced in one second is called Frequency of the wave. Unit: Hertz (Hz) or s^-1

Question 4.
Define : Wavelength (λ) and Timbre
Answer:
Wavelength (λ) : The maximum distance in which a sound wave repeats itself (or) In a Sound Wave the distance between the centres of two consecutive compressions (or) two consecutive rarefactions. Unit: metre (m).
Timbre: Timbre is the characteristic which distinguish two sounds of same loudness and pitch of two different instruments.

Question 5.
How are the Wavelength and frequency of a Sound wave related to its speed?
Answer:
Speed (v), Wavelength (λ) and frequency of sound (υ) are related by the following equation: Speed (v) = Wavelength (λ) × Frequency (υ) => v = λ × υ

Question 6.
What are the factors that intensity of Sound depends upon?
Answer:
The intensity of sound depends on the

• Amplitude of the source.
• Distance of the observer from the source.
• Surface area of the source.
• Density of the medium.
• Frequency of the source.

Question 7.
On which factors the speed of sound in gaseous medium depends?
Answer:

• Pressure of the medium.
• Temperature of the medium.
• Density of the medium.
• Nature of the medium.

Question 8.
On which factors the speed of sound in solid medium depends?
Answer:

• Elastic property of the medium.
• Temperature of the medium.
• Density of the medium.

Question 9.
Mention the fequency ranges of infrasoncis and ultrasonics.
Answer:

• Sound waves with frequencies below audible range is termed as Infrasonics.
  Infrasonics: Frequencies less than 20 Hz.
• Sound waves with frequencies above audible range is called as Ultrasonics.
  Ultrasonics: Frequencies greater than 20,000 Hz.

Question 10.
Why is a sound wave called a longitudinal wave?
Answer:
Sound wave is called a Longitudinal wave because

• It produces compressions and rarefactions in the air.
• The particles of air vibrates parallel to the direction of propagation.

Question 11.
Which characteristics of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer:
The Timbre (or) quality of sound enables us to identify our friend by his voice.

Question 12.
List the causes of noise pollution.
Answer:

• Hearing problems.
• Rupture of eardrum and hearing loss.
• Psychological damages.

Question 13.
Why are roots and walls of the auditorium covered with rough plaster?
Answer:
To reduce the effect of reverberation in large halls of the auditorium.

Question 14.
Give two practical applications of reflection of Sound?
Answer:

• SONAR – Reflection of sound is used to measure the distance, direction and speed of underwater objects.
• Stethoscope – Patient’s heartbeats reach doctor’s ear by multi reflections of sound.

Question 15.
What is acoustics?
Answer:
Acoustics is a branch of physics that deals with the study of properties of Sound.

VIII. Answer in detail :

Question 1.
Prove that sound needs a material medium for its propagation.
Answer:
To prove sound needs a material medium.

• Take an electric bell and an airtight glass jar connected to a vacuum pump.
• Suspend the electric bell inside the airtight jar and press the switch of the bell and hear the sound of the bell.
• Now pump out the air from the glass jar gradually.
• If the jar has vaccum, any sound will not be heard.
• So, sound needs a material medium to travel (here, it is air) and it is proved.

Question 2.
Distinguish between Loudness and Intensity of the Sound?
Answer:
Loudness

1. Loudness is a quantity by virtue of which sound can be distinguished.
2. The loudness of the sound is determined by its amplitude. Loudness a (Amplitude) .

Intensity

1. Intensity of the sound wave is defined as the amount of sound energy passing through unit area per second.
2. The amplitude of sound decides the intensity.

Question 3.
What is an echo? Write the conditions to hear an echo.
Answer:
A repeated sound that is caused by the reflection of sound waves from a surface.

Conditions for echo

• For echo, the time interval between the original sound and reflected sound must be 0.1 s. The sound must go to the obstacle and return to the listener on reflection after 0.1s.
• Total distance covered by the sound from source to the obstacle and reflected to listener must be atleast 340 ms^-1 × 0.1s = 34m.
• So the minimum distance of the obstacle from the source of sound = half of total distance
  \(\frac{34 \mathrm{~m}}{2}\) = 17m.
• This distance will change with the temperature of air.

Question 4.
Explain the working of human ear with diagram.
Answer:
Working of Human Ear
Parts of human ear are (i) outer ear, (ii) middle ear, (iii) inner ear.
(i) Outer ear [Pinna] : It collects the sound from the surroundings and directs towards auditory canal.
(ii) Middle ear : Sound reaches the auditory canal and vibrates the eardrum (or) tympanic membrane, a thin membrane.
Three small bones (hammer, anvil, stirrup) amplify the vibrations, several times. The middle ear transmits the amplified pressure variations to the inner ear.

(iii) Inner ear : (Cochlea) (j) Receives vibrations, (ii) converts them into electrical signals and (iii) they are sent to the Brain thro’ auditory nerve.
The Brain interprets the electrical signals to sound.

IX. Numerical problems :

Question 1.
The frequency of tuning fork is 484 Hz. What is the time period?
Solution :
Frequency of tuning fork, n = 484 Hz.

Question 2.
Velolcity of sound in air is 344 ms^-1 What is the range of wavelength of audible sound?
Solution :
Velocity of sound in air, v = 344 ms^-1
Audible frequency range = 20 – 20,000 Hz
We know V = \(v \lambda \Rightarrow \lambda=\frac{v}{v}\)
When Fequency v = 20Hz
\(\lambda=\frac{344}{20}=17.2 \mathrm{~m}\)
When Frequency, v = 20,000Hz
\(\lambda=\frac{344}{20,000}=0.0172 \mathrm{~m}\)
Range of wavelength of audible Sound = 0.0172 m- 17.2 m

Question 3.
A body vibrates 3000 times in one minute. If the velocity of sound in air 330 ms^-1, find (i) Frequency of vibration (ii) Wavelength.
Solution :
Velocity of sound in air, v = 330 ms^-1
No.of vibrations in a minute = 3000 / minute.
(i) Frequency, (Vibrations produced in one second)

Question 4.
A person is listening to a tone of 400 Hz from a distance of 500 m from the source of sound. What is the time interval between successive compressions from source?
Solution :
Fequency of tone u = 400 Hz.
Time interval between two
successive compressions
from source = Time period of wave.

Time interval between two successive compressions from source = 0.0025 s.

Question 5.
An echo returned in 3s. What is the distance of reflecting surface from the source given that the speed of sound is 330 ms^-1.
Solution :
Speed of sound, v = 330 ms^-1
Time of the echo, t = 3s.
Total distance travelled by the sound 2d = v × t = 330 × 3
2d = 990 m.
2d = Distance from source to reflecting surface + distance from reflecting surface to the listener.
So, distance from the source to reflected surface = \(\frac{\text { Total distance }}{2}\)
= \(\frac{2 d}{2}\)
Distance of the reflecting surface from the source = \(\frac{990}{2}\)
= 495m

Question 6.
Two persons are at opposite ends of a steel rod. One strikes the end of rod with a stone. Find the ratio of time taken by the sound wave in air and in steel to reach the second person. (Sound of speed in steel = 5960 ms^-1, Sound of speed in air = 344 ms^-1)
Solution :
Sound of speed in steel = 5960ms^-1
Sound of speed in air =344ms^-1

Question 7.
A Sound wave travels at a speed of 344 ms^-1. If the wavelength is 1.5 cm, what is the frequency of Wave? Will it be audible?
Solution :
Velocity of soung , v = 344ms^-1
Wavelength of sound. λ = 1.5cm

Audible frequency range = 20 – 20000Hz
So frequency 2,29,333 is not audible.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 9 Universe Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 9 Universe

9th Science Guide Universe Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Who proposed the heliocentric model of the universe?
(a) Tycho Brahe
(b) Nicolaus Copernicus
(c) Ptolemy
(d) Archimedes
Answer:
(b) Nicolaus Copernicus

Question 2.
Which of the following is not a part of outer solar system?
(a) Mercury
(b) Saturn
(c) Uranus
(d) Neptune
Answer:
(a) Mercury

Question 3.
Ceres is a …………….
(a) Meteor
(b) Star
(e) Planet
(d) Asteroid
Answer:
(d) Asteroid

Question 4.
The period of revolution of planet A around the Sun is 8 times that of planet B. How many times is the distance of planet A as great as that of planet B?
(a) 4
(b) 5
(e) 2
(d) 3
Answer:
(a) 4

Question 5.
The Big Bang occurred _____ years ago.
(a) 13.7 billion
(b) 15 million
(e) 15 billion
(d) 20 million
Answer:
(a) 13.7 billion

II. Fill in the blanks :

1. The speed of Sun in km/s is ………………
Answer:
250 km/s

2. The rotational period of the Sun near its poles is ………………
Answer:
36 days

3. India’s first satellite is ……………..
Answer:
Aryabhatta

4. The third law of Kepler is also known as the Law of ……………….
Answer:
Harmonics

5. The number of planets in our Solar System is …………………
Answer:
8

III. State whether true or false. If false, correct the statement:

1. ISS is a proof for international cooperation.
Answer:
True.

2. Halley’s comet appears after hearly 67 hours.
Answer:
False.
Correct statement: Halley’s comet appears after nearly 76 years.

3. Satellites nearer to the Earth should have lesser orbital velocity.
Answer:
False.
Correct statement: Satellites nearer to the Earth should have faster orbital velocity.

4. Mars is called the red planet.
Answer:
True.

IV. Answer briefly :

Question 1.
What is the solar system?
Answer:
The Sun and celestial bodies which revolve around it form the solar system. It consists of a large number of bodies such as planets, comets, asteroids, and meteors.

Question 2.
Define orbital velocity.
Answer:
The horizontal velocity that has to be imparted to a satellite at the determined height so that it makes a circular orbit around the planet is called “orbital velocity”.

Question 3.
Define time period of a satellite.
Answer:
Time taken by the satellite to complete one revolution around the Earth is called the time period.
Time period, T = Distance covered/Orbital velocity
T = 2πr/v

Question 4.
What is the satellite? What are the two types of satellites?
Answer:
A body moving in orbit around a planet is called a satellite.
The two types of Satellites are

1.  Natural satellites,
2.  Man-made satellites.

Question 5.
Write a note on the inner planets.
Answer:
The planets are spaced unevenly. The first four planets are relatively close together and close to the Sun. They form the inner solar system. The four planets grouped together in the inner solar system are Mercury, Venus, Earth, and Mars. They are called inner planets. They have a surface of solid rock crust and so are called terrestrial or rocky planets. Their insides, surfaces, and atmospheres are formed in a similar way and form a similar pattern. Our planet, Earth can be taken as a model of the other three planets.

Question 6.
Write about comets.
Answer:

• Comets are lumps of dust and ice that revolve around the Sim in highly elliptical orbits.
• Their period of revolution is very long.
• Comet vapourises and forms a head and tail on approaching the sun.
• Tail of the biggest comet may be around 160 million km.
• There are period comets (e:g) Halley’s comet which appears after every 76 years.

Question 7.
State Kepler’s laws.
Answer:
In the early 1600s, Johannes Kepler proposed three laws of planetary motion.
First Law – The Law of Ellipses
The path of the planets about the Sun is elliptical in shape, with the center of the Sun being located at one of the foci.

Second Law – The Law of Equal Areas
An imaginary line drawn from the center of the Sun to the center of the planet will sweep out equal areas in equal intervals of time.

Third Law – The Law of Harmonies
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their semi-major axis from the Sun.

Question 8.
What factors have made life on Earth possible?
Answer:
Factors responsible for life on Earth.

1. Right distance from the Sun.
2. Right temperature.
3. Presence of water.
4. Suitable atmosphere.
5. Blanket of ozone.

V. Answer in detail:

Question 1.
Give an account of all the planets in the solar system.
Answer:

The planets are spaced unevenly. The first four planets are relatively close together and close to the Sun. They form the inner solar system. Farther from the Sun is the outer solar system, where the planets are much more spread out. Thus the distance between Saturn and Uranus is much greater (about 20 times) than between the Earth and Mars.

The four planets grouped together in the inner solar system are Mercury, Venus, Earth, and Mars. They are called inner planets. They have a surface of solid rock crust and so are called terrestrial or rocky planets. Their insides, surfaces, and atmospheres are formed in a similar way and form a similar pattern. Our planet, Earth can be taken as a model of the other three planets.

The four large planets Jupiter, Saturn, Uranus and Neptune spread out in the outer solar system that slowly orbits the Sun are called outer planets. They are made of hydrogen, helium and other gases in huge amounts and have very dense atmosphere. They are known as gas giants and are called gaseous planets. The four outer planets Jupiter, Saturn, Uranus and Neptune have rings whereas the four inner planets do not have any rings. The rings are actually tiny pieces of rock covered with ice.

Question 2.
Discuss the benefits of ISS.
Answer:

1. Water purification efforts :
The water recovery system (WRS) and the oxygen generation system (OGS) techniques developed by ISS provides advanced water Alteration and purification to water scarcity areas

2. Eye-tracking technology :
Eye-tracking technology can be used in many laser surgeries which tracks eye’s position very accurately and helps the disabled people with limited movement and speech.

3. Robotic arms and Surgeries :
Robotic arms provide significant help to surgeons in removing inoperable tumours and taking biopsies with great accuracies.

4. Apart from the above, there are many other applications such as the development of improved vaccines, breast cancer detection and treatment, and so on.

Question 3.
Write a note on orbital velocity.
Answer:
Nowadays many artificial satellites are launched into the Earth’s orbit. The first artificial satellite Sputnik was launched in 1956. India launched its first satellite Aryabhatta on April 19, 1975. Artificial satellites are made to revolve in an orbit at a height of a few hundred kilometres. At this altitude, the friction due to air is negligible. The satellite is carried by rocket to the desired height and released horizontally with a high velocity so that it remains moving in a nearly circular orbit. The horizontal velocity that has to be imparted to a satellite at the determined height so that it makes a circular orbit around the planet is called orbital velocity.

The orbital velocity of the satellite depends on its altitude above Earth. The nearer the object to the Earth, the faster is the required orbital velocity. At an altitude of 200 kilometres, the required orbital velocity is a little more than 27,400 kph. That orbital speed and distance permit the satellite to make one revolution in 24 hours. Since Earth also rotates once in 24 hours, a satellite stays in a fixed position relative to a point on Earth’s surface. Because the satellite stays over the same spot all the time, this kind of orbit is called ‘geostationary’.

Orbital velocity can be calculated using the following formula.
v = \(\sqrt{\frac{\mathrm{GM}}{(\mathrm{R}+\mathrm{h})}}\)
where; G = Gravitational constant (6.673 × 10^{– 11}Nm²kg^{– 2})
M = Mass of the Earth (5.972 × 10²⁴kg)
R = Radius of the Earth (6371 km)
h = Height of the satellite from the surface of the Earth.

VI. Conceptual Questions

Question 1.
Why do some stars appear blue and some red?
Answer:

1. Stars appear in different colours depending on their temperatures.
2. Hot stars are white or blue in colour.
3. Cooler stars are orange or red in colour.

Question 2.
How is a satellite maintained in nearly circular orbit?
Answer:
Artificial satellites are made to revolve in an orbit at a height of a few hundred kilometres. At this altitude, the friction due to air is negligible. The satellite is carried by rocket to the desired height and released horizontally with a high velocity so that it remains moving in a nearly circular orbit.

Question 3.
Why are some satellites called geostationary?
Answer:
The Earth rotates once in 24 hours, a satellite stays in a fixed position.
Because the satellite stays over the same spot all the time, this kind of orbit is called . “geostationary”.

Question 4.
A man weighing 60 kg on the Earth will weigh 1680 kg in the Sun. Why?
Answer:
Mass of the man = 60Kg
w = m × g
m = 60Kg, g = 274.13m/s²
The sun’s gravitational acceleration is 30 times more than that of the earth. So the person would weigh 16,447N on the surface of the sun.

VII. Numerical Problems

Question 1.
Calculate the speed with which a satellite moves if it is at a height of 36,000 km from the Earth’s surface and has an orbital period of 24 hr (Take R = 6370 km).
[Hint: Convert hr into seconds before doing the calculation)

Solution:
Given:
Height of the satellite, h = 36,000 km = (36,000) ×10³m
Radius of the Earth, R = 6370 km = (6370) × 10³m
We know: Gravitational constant, G = 6.673 10^-11Nm²kg^-2
Mass of the Earth, M = 5.972 × 10²⁴kg.

Orbital velocity, v = 3.067×10 ³ m/s (or) 3067m/s (or) 3.067 km/s.

Question 2.
At an orbital height of 400 km, find the orbital period of the satellite.
Solution : Given : Orbital height, h = 400 km = 400 × 10³m
We know : Gravitational constant, G = 6.673 × 10^-11Nm²kg^-2
Mass of the earth, M =5.972 ×10²⁴kg
Radius of the Earth, R = 6371 km = 6371 × 10^-3m.

Intext Activities

ACTIVITY – 1

Form a team of three to four students. Prepare a poster about the astronomers

ACTIVITY – 2

Observe the sky keenly during night. Can you see group of stars? Can you figure out any shape? Discuss with your teachers and find out their name.
Aim : To observe the group of stars in the night sky.

Procedure :

1. Observe the night sky keenly.
2. Observe the movements of stars
3. Imagine the shapes

Observation :
By discussing with the teachers following groups are identified.

Group of Star	shape
1. Orion	Hunter
2. pisces	Fish
3. Gemini	Twins table
4. Leo	Lion
5. Cancer	Crab
6. Capricornus	Sea goat

ACTIVITY – 3

Watch the sky in the early morning. Do you see any planet? What is its name? Find out with the help of your teachers.
Aim :
1. Most of the planets cannot be seen in normal sky.
2. Few planets can be seen during some specific period in the night sky.
3. Mercury, closest to the sun can be seen from the earth.
4. Venus is also seen few days in a year.
5. Uranus may be also seen on odd days in October.

ACTIVITY – 4

Prepare a list of Indian satellites from Aryabhatta to the latest along with their purposes.
S.No. Name of satellite Year Purpose
s

9th Science Guide Universe Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
The Geocentric model of universe was proposed by ……………
(a) Tyago Brane
(b) Kepler
(c ) Ptolemy
(d) Copernicus
Answer:
ptolemy

Question 2.
The total area of observable universe is about light-years.
(a) 9.3 billion
(b) 93 billion
(c) 93 million
(d) 9.3 million
Answer:
93 billion

Question 3.
All the atoms together only make up ______ percent of universe.
(a) 3
(b) 4
(c) 5
(d) 2
Answer:
(b) 4

Question 4.
The milky way galaxy is ………………in shape.
(a) Elliptical
(b) Circular
(e) Spiral
(d) Irregular
Answer:
(c) spiral

Question 5.
Stars are built by ____ gases.
(a) Hydrogen
(b) Helium
(e) Nitrogen
(d) Oxygen
Answer:
(a) Hydrogen

Question 6.
The process that takes place in the Sun is ………………
(a) Nuclear Fission
(b) Spallation
(c) Nuclear Fusion
(d) None of these
Answer:(c)
Nuclear Fusion
Question 7.
The energy of the sun is radiated in the form of_____ Rays.
(a) Ultraviolet
(b) Infrared
(e) neutron radiation
(d) X-rays
Answer:
(b) Infrared

Question 8.
The ____ colour is the most intense colour in solar radiation.
(a) blue
(b) red
c) violet
(d) yellow
Answer:
(d) yellow

Question 9.
Athe distance of the planet from the sun increases, the period of revolution ………………..
(a) increases
b) decreases
(c) remains the same
(d) a & b
Answer:
(a) increases

Question 10.
Which among the planets has less length of a day?
(a) Mercury
(b) Uranus
(c) Jupiter
(d) Saturn
Answer:
(c) Jupiter

Question 11.
The hottest planet on the solar system is ……………….
(a) Venus
(b) Mercury
(c) Mars
(d) Earth
Answer:
(a) Venus

Question 12.
Which planet is known as Red Planet?
(a) Venus
(b) Saturn
(c) Mars
(d) Neptune
Answer:
(c) Mars

Question 13.
The number of moons present in Saturn is ………………..
(a) 20
(b) 30
(c) 50
(d) 60
Answer:
(d) 60

Question 14.
The planet having the longest summers and winters is ………………….
(a) Saturn
(b) Neptune
(c) Uranus
(d) Jupiter
Answer:
(c) Uranus

Question 15.
Windiest planet in the solar system ………………..
(a) Neptune
(b) Uranus
(c) Saturn
(d) Jupiter
Answer:
a) Neptune

Question 16.
Which among the planets does not have a moon?
(a) Mars
(b) Earth
(c) Uranus
(d) Mercury
Answer :
(d) Mercury

Question 17.
The orbital velocity of the satellite depends on its ……………………
(a) Shape of orbit
(b) altitude
(c) distance
(d) All of these
Answer:
(b) altitude

Question 18.
Which among the following statements is correct?
(i) Meteors are attracted by the gravitational at force of earth.
(ii) Meteors are travelling in low speeds.
(iii) Most of Meteors are burnt by the heat generated by friction in atmosphere.
(a) (i) & (ii)
(b) (ii) & (iii)
(c) (i) & (iii)
(d) All of these
Answer:
(c) (i) & (iii)

Question 19.
The first part of the ISS was launched by
(a) Russian Soyuz
(b) Russian Zarya
(c) Russian Orbital
(d) American Sputnik
Answer:
(b) Russian Zarya

Question 20.
The time is taken by the sun to complete one revolution around the milky way
(a) 250 million years
(b) 200 million years
(c) 225 million years
(d) 240 million years
Answer:
(c) 225 million years

Question 21.
Which of the following statements is correct?
A. There are eight planets in our Solar System.
B. Except Mars, all other planets revolve around the Sun in elliptical orbits.
(a) A only
(b) B only
(c) Both A and
(d) None
Answer:
(a) A only

II. Fill in the blanks :

1. Sun is the star present in the galaxy called ………………
Answer:
milky way

2. The universe began with the start of a massive explosion called ……………..
Answer:
Big Bang

3. Scientists believe that there are ……………… galaxies in the observable universe.
Answer:
one hundred billion (10¹¹)

4. Our closest neighbouring galaxy is ……………
Answer:
Andromeda

5.We can see nearly _______ stars with the naked eye in the dark night
Answer:
3000

6. The brightness of stars depends on their _______ and _____ from the earth.
Answer:
Intensity and distance

7. The Greek name for the Sun is …………………
Answer:
Helios

8. The sun is believed to be more than ______ years ago
Answer:
4.6 billion

9. The inner planets are also known as __________
Answer:
Rocky planets

10. The outer planets are also called as _____
Answer:
Gaseous planets

11. ______ is the brightest heavenly body in our night sky.
Answer :
Venus

12. ______ is called as giant planet
Answer :
Jupiter

13. ________ is the only moon iñ the solar system with clouds.
Answer :
Titan

14. Uranus is a ______ giant
Answer:
cold gas

15. Pluto crosses the orbit of Neptune in every ______
Answer :
248 years

16. The biggest asteroid is …………………
Answer :
Ceres

17. Satellites move around the planets due to ………….. and ……………… force.
Answer :
gravitý, the centripetal

18. The ratio of____ of the periods of any two planets is equal to the ratio of their semi-major axis from the Sun.
Answer :
squares, cubes

19. The temperature of the star is determined by ______
Answer :
Colour

20. ……………… is the only moon in the solar system that moves in the opposite direction to
the direction in which its planet spins.
Answer:
Triton

III. Match the following:

(I)

1.Mercury	a) Hottest planet
2.Saturn	b) Greenish star
3.Neptune	c) Rocky planet
4.Venus	d) Lightest planet

Answer:
1-c,2-d,3-b,4-a

(II)

1.Mars	a) Bluish-green planet
2.Jupiter	b) Cold gas giant
3. Earth	c) Giand planet
4. Uranus	d) Red planet

Answer:
1-d,2-c,3-a,4-b

(III)

1. Ganymede	a) Neptune
2. Triton	b) Jupiter
3. Titan	c) Mars
4. Phobas	d) Saturn

Answer:
1-b,2-a,3-d,4-c,
(IV)

1. Jupiter	a)17.2 hours
2. Mercury	b)10.7 hours
3. Venus	c) 87.97 days
4. Saturn	d) 9 hours 55 min
5. Mars	e) 243 days
	f) 87.97 days
	g) 24 hours 37 min

Answer:
1-d,2-c,3-e,4-b,5-g

IV. State whether true or false. If false, correct the statement:

1. The basic constituent of the universe is the luminous matter.
Answer:
True.

2. The important thing about universe is that it is currently shrinking.
Answer:
False.
Correct statement: The important thing about the universe is that it is currently expanding.

3. All the matter in the universe is made up of hydrogen and helium.
Answer:
True.

4. Stars also appear to be in different colours depending on their composition of Gases.
Answer:
False.
Correct statement: Stars also appear to be in different colours depending on their temperature.

5. The planets are revolving around the sun because of the gravitational force of attraction between them.
Answer:
True.

6. The rotation of the sun near the poles takes around 25.4 days.
Answer: False.
Correct statement: The rotation of the Sun near the poles takes around 36 days.

7. Mercury is a special planet from the Sun, almost the same size as Earth.
Answer:
False.
Correct statement: Venus is a special planet from the Sun, almost the same size as Earth.

8. The axis of rotation of the Earth is perpendicular to the plane of its orbit.
Answer:
False.
Correct statement: The axis of rotation of the Earth is not perpendicular to the plane of its orbit.

9. Pole star is not visible from the southern hemisphere.
Answer:
True.

10. Comets revolve around the Sun in highly spiral orbits.
Answer:
False.
Correct statement: Comets revolve around the Sun in highly elliptical orbits.

11. The distance between Saturn and Uranus is about 10 times that between Earth and Mars.
Answer:
False.
Correct statement: The distance between Saturn and Uranus is about 20 times that between Earth and Mars.

V. Assertion and Reason type questions :

Mark the correct choice as :
(a) If both assertion and reason are true and Reason is the correct explanation of Assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion. ,
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.

Question 1.
Assertion: Earth appears bluish-green.
Reason: This is due to the reflection of light from water and land mass on its surface.
Answer:
(a) If both assertion and reason are true and Reason is the correct explanation of Assertion.

Question 2.
Assertion: Sun is a medium-sized star.
Reason: Sun is situated at the centre of the solar system.
Answer:
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion

Question 3.
Assertion : The outer planets are called as Terrestial Planets.
Reason : Outer planets are made up of hydrogen, helium and other gases in huge amounts and have very dense atmospheres.
Answer:
(d) Assertion is false but reason is true
Assertion : The outer planets are called as Gas giants.

Question 4.
Assertion : The period of revolution of a satellite around a planet is directly proportional to the radius of the orbit of the satellite.
Reason : Artificial satellites do not follow Kepler’s Laws of motion.
Answer:
(c) Assertion is true but reason is false
Reason : Artificial satellites follow Kepler’s laws of motion.

Question 5.
Assertion : At the pole, the value of acceleration due to gravity (g) is greater than equator.
Reason : Earth rotates on its axis in addition to revolving around the sun.
Answer:
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion

VI. Very Short Answer questions :

Question 1.
What is the universe?
Answer:
The collection of all the things that exist in space is known as the universe.

Question 2.
What is a galaxy?
Answer:
A galaxy is a massive collection of gas, dust and billions of stars and their solar systems.

Question 3.
How are galaxies classified?
Answer:
Depending on their appearance, galaxies are classified as

• Spiral,
• Elliptical, (or)
• Irregular.

Question 4.
Why is our galaxy called Milky way?
Answer:
Our galaxy is called milky way galaxy, because it appears as a Milky band of light in the sky.

Question 5.
What is an orbit?
Answer:
A definite curved path in which a planet revolves around the sun is called an orbit.

Question 6.
Define Period of rotation.
Answer:
The time taken by a planet to complete one rotation is called its period of rotation.

Question 7.
Give a reason for changes of seasons on Earth.
Answer:

• Earth is not perpendicular to the plane of its orbit.
• This tilt is responsible for the change of seasons on earth.

Question 8.
Mention the factors responsible for motion of satellite.
Answer:

• Gravity and
• The centripetal force are the factors responsible for motion of satellite

Question 9.
What is a geostationary orbit?
Answer:
A satellite stays in a fixed position relative to a point on Earth’s surface. That is, the satellite stays over the same spot all the time. This kind of orbit is called “Geostationary Orbit”.

Question 10.
How is eye-tracking technology helpful?
Answer:
Eye-tracking technology is helping disabled people with limited movement and speech.

Question 11.
What is a cosmic year?
Answer:
The sun travelling at a speed of 250 km per second (9 lakhs km/h) takes about 225 million years to complete one revolution around the Milky Way. This period is called a cosmic year.

Question 12.
Why are we able to see the Moon even though it is not a luminous body?
Answer:
are able to see the moon, because it reflects the light of the Sun

VII. Answer briefly :

Question 1.
Write notes on the Milky Way.
Answer:

1. Milky Way galaxy is spiral in shape.
2. It is made up of approximately 100 billion stars.
3. Its diameter is 1,00,000 light years.
4. Our solar system is 25,000 light-years away from the centre of our galaxy.

Question 2.
How does a planet differ from a star?
Answer:

Star	Planet
1. Star is luminous body (emit their own light).	Planet is a non-luminous body, (does not emit light). table
2. It revolves in the galaxy-without any centre.	Planet revolves around the star.

Question 3.
Briefly explain (i) brightness (ii) colour of star.
Answer:
Brightness of star:
The brightness of a star depends upon their intensity and distance from the earth. Colour of star:

1. The colour of the stars depends on their temperature.
2. Hot stars are white or blue.
3. Cooler stars are orange or red in colour.

Question 4.
What is a constellation?
Answer:

1. A group of stars forming an imaginary outline or meaningful pattern on the space is called a constellation.
2. They represent an animal, mythological person or creature or an object.
3. 

Question 5.
How is life on earth supported?
Answer:

1. Life on earth is supported by Sun.
2. Solar energy from the Sim has supported and sustained terrestial existence on Earth since the beginning of time.

Question 6.
Write short notes on Asteroids.
Answer:

1. 1. Half a million pieces of rocks that were left over when the planets were formed are called Asteroids.
2. Asteroids revolve around the Sun.
3. Asteroids can only be seen through large telescope.
4. The biggest asteriod is Ceres.

Question 7.
Differentiate Meteors and Meteorites?
Answer:

Meteors	Meteorites
Small pieces of rocks that are burnt up by the heat generated due to friction in the Earth’s atmosphere.	Bigger pieces of rocks that are not completely burnt by heat and fall on the surface of the Earth.

Question 8.
Write down the formula of orbital velocity.
Answer:
v = \(v=\sqrt{\frac{\mathrm{GM}}{(\mathrm{R}+h)}}\)
where v = Orbital velocity.
G = Gravitational constant. (6.673 × 10^-11Nm ²kg^-2
M = Mass of the Earth (5.972 × 10²⁴kg)
R = Radius of Earth (6371 km)
h = Height of thé satellite from the surface of the Earth.

Question 9.
Write short notes on Halley’s comet.
Answer:

1. Halley’s comet is a periodical comet.
2. It appears after nearly everý 76 years.
3. It was last seen in 1986 and will next be seen in 2062

Question 10.
Mention the uses of Robotic arms.
Answer:
Robotic arms

1. Helps in removing inoperable tumours.
2. Takes biopsies with great accuracy.
3. Helpful in breast cancer detection and treatment.
4. Helpful in the development of improved vaccines.

VIII. Answer In detail:

Question 1.
Explain the salient features of the Big Bang Theory.
Answer:
According to the Big Bang Theory,

1. The universe was a hot dense matter.
2. 13.7 billion years ago, an explosion occurred.
3. All the matter is ejected in all directions in the form of galaxies.
4. The galaxies consist of stars which are held together by gravity.
5. The stars explode and planets are liberated throughout the Universe.

Question 2.
How is Sun formed according to Big Bang theory?
Answer:
According to the Big Bang theory.

1. Hydrogen gas condensed to form huge clouds.
2. Some of the hydrogen gas was left free and started floating around. in our galax
3. The free-floating hydrogen gas concentrated and paved way for the formation Sun and solar system.
4. The Sun and solar system turned into a slowly spinning molecular cloud, composed of hydrogen and Helium molecules.
5. The clouds undergo compression due to gravity.
6. The excessive and high-speed spinning of cloud results in flattening into a giant disc.

Question 3.
Give a comparative account of satellites and rings of planets.
Answer:

IX. Numerical problems :

Question 1.
The Earth’s distance from the Sun is 149.6 × 10⁶km and the period of Earth’s revolution is 1 year. Calculate the ratio of the squares of the periods to cubes of the major axis.
Solution :
Semi major axis from sun, R = 149.6 × 10⁶ km.
Period of Earth, T = 1 year.
The ratio = \(\frac{T^{2}}{R^{3}}=\frac{(1)^{2}}{\left(149.6 \times 10^{6}\right)^{3}}\) = 2.98 ×10^-25 year² / km ³.

Question 2.
The mean distance of Earth from the Sun is 149.6 × 10⁶ km and the mean distance of mercury from the sun is 57.9× 10⁶km. The period of Earth’s revolution is 1 year. What is the period of Mercury’s revolution? .
Solution: Given
1. Mean distance of Earth from Sun, r1 = 149.6 × 10 ⁶
2. Mean distance of Mercury from sun, r2 = 57.9 × 10⁶
3. The period of Earth’s revolution, T1 = 1 year
4. The period of Mercury’s revolution, T2 = ?
According to Keplar’s Third Law


Question 3.
Calculate the speed and period of revolution of satellite orbiting at a height 700 km above the Earth’s surface.
Solution:
Given: 1. Height of th Satellite, h = 700 km = 700 x 103 m
We Know: 2. Gravitational constant G = 6.673 × 0^-11 Nm2 kg^-2
3. Mass of the Earth, M = 5.972 × 1024 kg
4. Radius of Earth, R = 6371 km = 6371 × 10³ m
Formula (R + h) = (6371 + 700)km = 7071 km
= 7071 × 10³m=0.7071 × 10⁷m

Period of Revolution T = 5.9 15 × 10³ s
= 5915 sec. (or) 98 min 35 sec.

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 11 Atomic Structure Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 11 Atomic Structure

9th Science Guide Atomic Structure Text Book Back Questions and Answers

I. Choose the correct answer :

Question 1.
Among the following the odd pair is

Answer:

Question 2.
Change in the number of neutrons in an atom changes it to
(a) an ion.
(b) an isotope.
(c) an isobar.
(d) another element.
Answer:
(b) an isotope

Question 3.
The term nucleons refer to
(a) protons and electrons
(b) only neutrons
(c) electrons and neutrons
(d) protons and neutrons
Answer::
(d) protons and neutrons

Question 4.
The number of protons, neutrons and electrons present respectively in \({ }_{35}^{80} \mathrm{Br}\) are
(a) 80,80,35
(b) 35,55,80
(c) 35,35,80
(d) 35,45,35
Answer:
(d) 35,45,35

Question 5.
The correct electronic configuration of potassium is
(a) 2,8,9
(b) 2,8,1
(c) 2, 8, 8, 1
(d) 2, 8, 8, 3
Answer:
(c) 2, 8, 8,1

II. State whether true or false. If false, correct the statement:

1. In an atom, electrons revolve around the nucleus in fixed orbits.
Answer:
True.

2. Isotopes of an element have different atomic numbers.
Answer:
False.
Correct statement: Same atomic numbers but different mass numbers.

3. Electrons have negligible mass and charge.
Answer:
True.

4. Smaller the size of the orbit, lower is the energy of the orbit.
Answer:
True.

5. The maximum number of electron in L Shell is 10.
Answer:
False.
Correct statement :The maximum number of electrons in L Shell is 8.

III. Fill in the Blanks :

1. Calcium and Argon are examples of a pair of ………….
Answer:
isobars

2. Total number of electrons that can be accommodated in an orbit is given by …………..
Answer:
the formula 2n²

3. ………….isotope is used in the nuclear reactors.
Answer:
Uranium-235

4. The number of neutrons present in \({ }_{3}^{7} \mathrm{Li}\) is ………….
Answer:
4

5. The valency of Argon is ………………
Answer:
Zero

IV. Match the following :

a) Dalton	1. Hydrogen atom model
b) Chadwick	2. Discovery of nucleus
c) Rutherford	3. First atomic theory
d) Neils Bohr	4. Plum pudding model
	5. Discovery of neutrons

Answer:
a – 3, b – 5, c – 2, d – 1.

V. Complete the following table :

Answer:

VI. Answer very briefly :

Question 1.
Name an element which has the same number of electrons in its first and second shell.
Answer:
Beryllium. Atomic number – 4 (K-shell-2, L-shell-2)

Question 2.
Write the electronic configuration of K and Cl
Answer:

Question 3.
Write down the names of the particles represented by the following symbols and explain the meaning of superscript and subscript numbers attached. ₁H¹, ₀n¹, _-1C⁰
Answer:
₁H¹ – hydrogen atom mass number 1. Atom number 1.
₀n¹– neutron change 0. Mass 1 amu.
_-1C⁰ – electron change -1. Mass negligible.

Question 4.
For an atom ‘X’, K, L, and M shells are completely filled. How many electrons will be present in it?
Answer:
K – 2, L – 8, M – 18, 28 electrons – Nickel

Question 5.
What is the same about the electron structures of:
a. Lithium, Sodium and Potassium.
b. Beryllium, Magnesium and Calcium.
Answer:
a. Lithium, sodium & potassium have 1 electron in their outermost shell.
b. Beryllium, magnesium and calcium have 2 electrons in their outermost shell.

VII. Answer briefly :

Question 1.
How was it shown that atom has empty space?
Answer:
Rutherford performed an experiment of bombarding a thin gold foil with very small positively charged particles called a particles. He observed that most of the alpha particles passed straight through the foil. He infered by thin experiment that most of the space in the atom is empty.

Question 2.
Why do \({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\) have the same chemical properties? In what respect do these atoms differ?
Answer:
\({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\) have same chemical properties because they have same number of electrons but their atoms differ in the number of neutrons.

Question 3.
Draw the structure of oxygen and sulphur atoms.
Answer:

Question 4.
Calculate the number of neutrons, protons and electrons :
(i) atomic number 3 and mass number 7
(ii) atomic number 92 and mass number 238.
Answer:
(i) atomic number 3 and mass number 7
∴ No. of electrons (or) No. of protons = 3
Mass number = No. of protons + No. of neutrons
∴ No. of neutrons = 7-3=4

(ii) atomic number 92 and mass number 238
Atomic number = 92
∴ No. of electrons = 92
No. of protons = 92
No. of neutrons = 238-92 = 146

Question 5.
What are nucleons? How many nucleons are present in Phosphorous? Draw its structure.
Answer:

The number of protons and neutrons present in the nucleus are called nucleons. The number of nucleons present is phosphorus is 31.

VIII. Answer in detail :

Question 1.
What conclusions were made from the observations of Gold foil experiment?
Answer:

In Rutherford’s Alpha ray scattering experiment, the following conclusions were made from the observations.

• Atom has a very small nucleus at the centre.
• There is a large empty space around the nucleus.
• The entire mass of an atom is concentrated in a very small positively charged region, which is called Nucleus.
• The electrons are distributed in the vacant space around the nucleus.
• The electrons move in circular paths around the nucleus.

Question 2.
Explain the postulates of Bohr’s atomic model.
Answer:
The main postulates are:

• In atoms, electrons revolve around the nucleus in stationary circular paths called orbits or shells or energy levels.
• While revolving in orbits the electrons do not radiate energy.
• The circular orbits are numbered as 1,2,3,4,… or designated as K, L, M, N, shells. These numbers are referred to as principal quantum numbers (n).
• K shell (n=l) is closest to the nucleus and is associated with lowest energy.
• The energy of each orbit or shell is a fixed quantity and the energy is quantized.

Question 3.
State Gay Lussac’s law of combining volumes, explain with an illustration.
Answer:
Whenever gases react together, the volumes of the reacting gases as well as the products, if they are gases, bear a simple whole number ratio, provided all the volumes are measured under similar conditions of temperature and pressure.
Example:
Step 1: Hydrogen combines with oxygen to form water (word equation) Hydrogen + Oxygen → Water.

i. e. Two volumes of hydrogen reacts with one volume of oxygen to form two volumes of water vapour, i.e. the ratio by volume which gases bears is 2:1:2 which is a simple whole number ratio.
It follows that at a given temperature and pressure, the volumes of all gaseous reactants and products bear a simple whole number ratio to each other.

Intext Activities

ACTIVITY – 1

Symbolically represent the following atoms using the atomic number and mass number, a) Carbon b) Oxygen c) Silicon d) Beryllium
Answer:

ACTIVITY – 2

Assign the valency for Phosphorus, Chlorine, Silicon and Argon
Answer:
Phosphorus – P – 3, 5
Chlorine – Cl – 1
Silicon – Si – 4
Argon – Ar – 0

ACTIVITY – 4

Draw the structures of the isotopes of oxygen O¹⁶ and O¹⁸
Atomic number of oxygen = 8.
Answer:

ACTIVITY – 5

Draw the model of the following pairs of isotones:
(i) Fluorine & Neon (ii) Sodium & Magnesium (iii) Aluminum and Silicon.
Answer:

ACTIVITY – 6

Nitrogen combines with hydrogen to form ammonia (NH3). Illustrate Gay Lussac’s law using this example.
Answer:

1 volume of nitrogen reacts with 3 volumes of hydrogen to form 2 volumes of ammonia gas. The ratio by volume which gases bear is 1 : 3 : 2. Which is a simple while number ratio.

Test Yourself :

Question 1.
Calculate the number of neutrons in the following atoms:

Answer:
Number of neutrons (n) = Mass number (A) – Atomic number (z)
a) \(\frac{27}{13} \mathrm{Al}\) ⇒ Number of neutrons (n) = 27 – 13 = 14
b) \(\frac{31}{15} \mathrm{P}\) ⇒ Number of neutrons (n) = 31-15 = 16
c) \(\frac{190}{76} \mathrm{Os}\) ⇒ Number of neutrons (n) = 190 – 76 = 114
d) \(\frac{54}{24} \mathrm{Cr}\) ⇒ Number of neutrons (n) = 54 – 24 = 30

9th Science Guide Atomic Structure Additional Important Questions and Answers

I. Choose the correct answer :

Question 1.
Hydrogen atom does not have …………………..
(a) Proton
(b) Neutron
(c) Electron
(d) Proton and electron
Answer:
(b) Neutron

Question 2.
An electron has ……………………
(a) Mass 1/1837^th of proton and positively charged
(b) Mass equal to proton and positively charged.
(c) Mass 1 / 1837^th of proton and negatively charged.
(d) Mass equal to proton and negatively charged.
Answer:
(c) Mass 1/1837^thof proton and negatively charged

Question 3.
Which statement is not correct about isotopes of an element?
(a) Their chemical properties are same.
(b) Their atomic number is same.
(c) Number of electrons are different.
(d) Number of neutrons are different.
Answer:
(c) Number of electrons are different

Question 4.
Co-60 is used in the treatment of …………………..
(a) Cancer
(b) Thyroid disorders
(c) Leukemia
(d) Blockage of arteries.
Answer:
(a) Cancer

Question 5.
Every atom has an equal number of protons and electrons. The nature of the atom is …………………..
(a) Positive
(b) Neutral
(c) Negative
(d) None of the above
Answer:
(b) Neutral

Question 6.
Gold foil alpha particle scattering experiment was performed by …………………..
(a) Dalton
(b) Goldstein
(c) Thomson
(d) Rutherford
Answer:
(d) Rutherford

Question 7.
Which subatomic particles have no charge …………………..
(a) Proton
(b) Neutron
(c) Electron
(d) Proton and electron
Answer:
(b) Neutron

Question 8.
The outermost shell of an atom cannot accommodate electrons more than
(a) 2
(b) 8
(c) 18
(d) 32
Answer:
(b)8

Question 9.
The ratio of masses of oxygen in CO and C02 for fixed mass of carbon is 1 : 2. The above is the law of ……………………
(a) Law of multiple proportions
(b) Law of reciprocal proportions
(c) Gay Lussac’s Law of combining volumes
(d) None of the above
Ans:
(a) Law of multiple proportions

Question 10.
………………….. is a radioactive isotope present in our bodv.
(a) Cobalt 60
(b) Uranium 235
(c) Iodine 131
(d) Potassium 40
Answer:
(d) Pottassium 40

Question 11.
Proton was discovered by ………………….
(a) Rutherford
(b) Goldstein
(c) Chadwick
(d) J.J. Thomson
Answer:
(a) Rutherford

Question 12.
Electron was discovered by …………………..
(a) J.J. Thomson
(b) Rutherford
(c) Goldstein
(d) Chadwick
Answer:
(a) J.J. Thomson

Question 13.
α – particles are …………………..
(a) Negative charged particles
(b) Positive charged particles
(c) Beam of Neutrons
(d) gamma radiation
Answer:
(a) Negative charged particles

Question 14.
An α – particle is …………………..
(a) hydrogen Nucleus
(b) a Helium Nucleus
(c) a Proton
(d) an electron
Answer:
(b) a He Nucleus

Question 15.
The electronic configuration of an atom is 2,8,3. The valency of the atom is ……………………
(a) 13
(b) 10
(c) 3
(d) 8
Answer:
(c) 3

Question 16.
The No. of electrons in the outermost shell of the atom of an inert gas ……………………
(a) 0
(b) 1
(c) 2
(d) 8
Answer:
(d) 8

Question 17.
Which one of the following will have the maximum charge / mass ratio?
(a) Electron
(b) Proton
(c) Neutron
(d) a – Particle
Answer:
(a) Electron

Question 18.
The maximum No. of electrons that can be accommodated in M shell is ……………………
(a) 2
(b) 8
(c) 18
(d) 32
Answer:
(c) 18

Question 19.
Elements with valency 1 are ……………………
(a) always metals
(b) always metaloids
(c) either metals (or) non-metals
(d) always non – metals
Answer:
(a) always metals

Question 20.
The electronic configuration of ‘Cl’ is ……………………
(a) 2,7
(b) 2,8,8,7
(c) 2,8,7
(d) 2,7,8
Answer:
(c) 2, 8, 7

Question 21.
The isotope used to remove the brain tumour and treatment of Cancer is ……………………
(a) Cobalt 60
(b) Uranium 235
(c) Iodine 131
(d) Na – 24
Answer:
(a) Cobalt 60

II. Fill in the Blanks :

1. ………………….. are the building blocks of matter.
Answer:
Atoms

2. The combination of different elements to form a compound is governed by certain basic rules called …………………..
Answer:
Laws of chemical combination

3. Volume of the nucleus of an atom is ………………….. compared to the volume of the extranuclear part of the atom.
Answer:
very small

4. the Atomic number of an element is 20. It has………………….. valence electrons.
Answer:
2

5. Atoms are so tiny their mass number cannot be expressed in grams but expressed in…………………..
Answer:
atomic mass unit (amu)

6. Elements having completely filled outermost shell, show………………….. valency.
Answer:
Zero

7. A ………………….. number describes a specific aspect of an electron.
Answer:
quantum

8. When an atom gives electrons from its outermost shell, it becomes ………………….. charged.
Answer:
positively

9. The elementary particles such as protons and neutrons are collectively called as…………………..
Answer:
nucleons

10. In two isotopic species number of protons is same but the number of………………….. is different.
Answer:
Neutrons

11. The combination of different elements form a…………………..
Answer:
Compound

12. A compound is governed by basic rules are known as ……………………
Answer:
Laws of chemical combination

13. The ratio of masses of H and O in H₂O is…………….
Answer:
1 : 8

14. α, β, γ rays are during the ratio active decay of an atom.
Answer:
emitted

15. Beryllium + α – rays → Carbon +……………….
Answer:
Neutron

16. …………… = No. of protons = No. of the electrons.
Answer:
Atomic No.

17. ‘A’ is denoted by …………………
Answer:
Mass No

18. ‘Z’ is denoted by . …………………
Answer:
Atomic No

19. Mass No =………………… + No. of Neutrons
Answer:
No. of protons

20. The Mass No. of 27 is for the element…………………….
Answer:
Aluminium

21. U-235 Isotope is used as ………………….
Answer:
Fuel in nuclear reactors

22. The symbol of phosphorus is ……………………….
Answer:
P

23. Na – →……………….. Na⁺.
Answer:
e-

24. Elements with 4 to 7 in their valence shells are …………………
Answer:
non -metals

25. Valency of the elements having ……………..is 1, 2, 3 respectively.
Answer:
Valence electrons 1, 2, 3

26. Atomic orbitals allow atoms to make…………………….. bonds
Answer:
Co-valent

27. The symbol of Azimuthal quantum number is……………………..
Answer:
l

28. The symbol of the Principal quantum number is……………………..
Answer:
n

29. Valency is the combining capacity of ……………………..
Answer:
an atom

III. State whether true or false. If false, correct the statement:

1. In Rutherford’s experiment, bouncing of alpha particles suggests that nucleus of an atom is negatively charged.
Answer:
False
Correct statement: Nucleus of an atom is positively charged.

2. Electrons revolve around the nucleus in definite open shells.
Answer:
False
Correct statement: Electrons revolve around the nucleus in definite closed shells.

3. K and L shell can accommodate a maximum 2 and 8 electrons respectively.
Answer:
True

4. Radio activity of Carbon 14 is considered to determine the age of object, especially of archeological importance.
Answer:
True

5. In a neutral atom number of protons is equal to the number of neutrons.
Answer:
Correct statement: In a neutral atom number of protons is equal to the number of
electrons.

6. If an atom has 6 electrons in its outermost shell, it is inert.
Answer:
Correct statement: If an atom has 8 electrons in its outermost shell, it is inert.

7. The valency of Chlorine is 7.
Answer:
Correct statement: The valency is 1.

8. Smaller the size of the orbit, the smaller the energy of the orbit.
Answer:
True

9. The stability of the nucleus is determined by the Neutron – Proton ratio.
Answer:
True

10. Isotopes of elements have the same chemical properties.
Answer:
True

IV. Match the following :

1.

Column A	Column B
1) Prinicipal quantum number	a) Orientation of orbitals
2) Azimuthal quantum number	b) Spin of the electron
3) Magnetic quantum number	c) Main energy level
4) Spin quantum number of orbital	d) Sub shell/shape of orbital

Answer:
1) – c, 2) – d, 3) – a, 4) – b

2.

Column A	Column B
1. K shell	a) 8
2. L shell	b) 32
3. M shell	c) 2
4. N shell	d) 18

Answer:
1) – c, 2) – a, 3) – d, 4) – b

3.

Column A	Column B
a) Mass of proton	1. +1
b) Mass of electron	2. -1
c) Charge of electron	3. 9.31 x 10-28g
d) Charge of proton	4. 1.67 x 10-24g

Answer:

a) 4
b) 3
c) 2
d) 1

V. Answer very briefly :

Question 1.
If and element M has mass number 24 and atomic number 12, how many neutrons does its atom contain?
Answer:
Mass number = No. of protons + neutrons
Atomic number = No. of protons
No. of neutrons = 24 – 12 = 12.

Question 2.
Atomic number of A and B are 18 and 19 respectively. What is the electronic configuration of A and B?
Answer:
Electronic configuration of A = 2, 8, 8
Electronic configuration of B = 2, 8, 8, 1.

Question 3.
How will you define the term ‘electronic configuration’?
Answer:
The systematic arrangement of electrons in various shells or orbits in an atom is called the electronic configuration.

Question 4.
Why do the chemical properties of an element are determined by valence electrons?
Answer:
Because they are the one which takes part in the chemical reaction.

Question 5.
What are the elements which have valence electrons 1 or 2 or 3 are called and what are the elements with valence Electrons 4 to 7 in their valence shells?
Answer:
Elements with valence electrons 1 or 2 or 3 are metals and valence electrons with 4 to 7 are non – metals.

Question 6.
How is an atom of the element represented? Give an example.
Answer:
If ‘X’ is the element, atomic mass at the upper left side and atomic number at the lower left side of the symbol of the element.
Example : \({ }_{11}^{23} \mathrm{Na}\) ⇒ 23 →Atomic Mass, 11 →Atomic number.

Question 7.
Why an atom is considered neutral?
Answer:
An atom of an element contains equal number of positively charged protons and negatively charged electrons and so it is neutral.

Question 8.
Name the scientist and his experiment to prove that nucleus of an atom is positively charged.
Answer:
Name of the scientist – Earnest Rutherford
Name of the experiment – Gold foil alpha particle scattering experiment.

Question 9.
Name the particles which determine the mass of an atom?
Answer:
The mass of an atom is determined by protons and neutrons.
Atomic mass = No. of protons + No. of neutrons.

Question 10.
What are the shells?
Answer:
Different energy levels outside the nucleus are called as shells. They are designated as K, L, M, N and numbered as 1, 2, 3…..

Question 11.
Rutherford’s model of an atom has a very small ………….. at the center.
Answer:
Nucleus.

Question 12.
Niels Bohr was Born on …………
Answer:
October 7, 1885.

Question 13.
When an electron returns from high energy level to lower energy level it gives …………
Answer:
It gives off energy.

Question 14.
In \({ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X}\)what are the letters A, Z, X stand for?
Answer:
X → symbol of element
Z →Atomic No.
A → Mass No.

VI. Answer briefly :

Question 1.
State the law of reciprocal proportion.
Answer:
If two different elements combine separately with the same weight of a third element, the ratios of the masses in which they do so are either the same or a simple multiple of the mass ratio in which they combine.

Question 2.
Why proton is considered to be the fingerprint of an atom?
Answer:
An atom of an element has its own characteristic number of protons in its nucleus, which distinguishes it from the atoms of other elements. Hence proton is considered to be the fingerprint of an atom.
This characteristic number (Number of protons) is called the atomic number of the element. The atomic number is denoted by Z.

Question 3.
How can an element be identified on the Periodic Table? What makes an element different from another element?
Answer:
An element can be identified by its atomic number which is a representation of the number of protons contained in the nucleus of a particular element. The amount of protons of an element never changes.

Question 4.
Because atoms are so small, what do scientists do?
Answer:
Since atoms are so small, scientists create models to describe them. A model may be a diagram, mental picture, a mathematical statement or an object that helps explain ideas about the natural world.

Question 5.
What are isotopes?
Answer:
Atoms of the same element with the same number of protons and a different number of neutrons – the number of protons will never change! Ex.: Carbon 12, Carbon 13 and Carbon 14 are isotopes of the element carbon.

Question 6.
Draw the diagram of laws of chemical combination.
Answer:
Laws of chemical combination

Question 7.
Define Isobars.
Answer:
Isobars are the atoms of the different elements of same mass number but different atomic number.

Question 8.
What is a combination reaction?
Answer:
A combination reaction is a reaction where two or more substances combine to form a single substance.
The combination of different elements to form a compound is governed by certain basic rules. These rules are known as Laws of chemical combination.

Question 9.
What are the salient features of Rutherford’s model of an atom?
Answer:
RUTHERFORD’S MODEL OF AN ATOM- Salient features

• Atom has a very small nucleus at the center.
• There is large empty space around the nucleus.
• Entire mass of an atom is concentrated in a very small positively charged region which is called the nucleus.
• Electrons are distributed in the vacant space around the nucleus.
• The electrons move in circular paths around the nucleus.

Question 10.
What are the Limitations of Bohr’s Model?
Answer:
Limitations of Bohr’s model:

• One main limitation was that his model was applicable only to Hydrogen.
• It could not be extended to multi-electron atoms.
• Hence more research and deeper study of atoms became necessary.

Question 11.
Explain the Composition of the Nucleus.
Answer:
COMPOSITION OF NUCLEUS

• Electrons have a negligible mass; hence the mass of the atom mainly depends on the mass of the nucleus. Nucleus of an atom consists of two components, they are protons and neutrons.
• Protons are positively charged. Protons repel each other because of their like charges. Hence more than one proton cannot be packed in a small volume to form a stable nucleus, unless neutrons are present.
• Neutrons reduce the repulsive force between the positively charged protons and contribute to the force that holds the particles in the nucleus together.

Question 12.
Define the Nucleons.
Answer:
Nucleons: The elementary particles such as protons and neutrons are collectively called as Nucleons.

Question 13.
What are the relation between mass no. & atomic no?
Answer:
Relationship between Mass Number and Atomic Number:
Mass Number (A) = Number of Protons + Number of Neutrons(n)
Atomic Number (Z) = Number of Protons or Number of Electrons
Mass Number = Atomic Number (Z) + Number of neutrons (n)
A = Z + n.

Question 14.
What are the types of Quantum Number?
Answer:

Question 15.
Draw the atomic structure of Mg (At. No. 12, Mass No. 24)
Answer:

Question 16.
Compare the charge and mass of protons and electrons.
Answer:

Question 17.
Ca²⁺ has completely filled outer shell. Justify your answer.
Answer:
The atomic number of Calcium is 20. It has K = 2, L = 8, M = 8, N = 2.
If we remove the last 2 electrons, that is from N shell, Ca2+ and we will be having 8 in the outermost shell (M shell). So we have completely filled outer shell. (The maximum 8 electrons in a shell is a completely filled shell).

Question 18.
State the law of multiple proportion. .
Answer:
When two elements A and B combine together to form more than one compound, then masses of A which separately combines with a fixed mass of B are in simple ratio.

Question 19.
List the uses of isotopes.
Answer:
Uranium 235 – Used as fuel in nuclear reactors
Cobalt 60 – Used in the treatment of cancer
Iodine 131 – Used in the treatment of goitre.
Carbon 14 – To find the age of plants and animals.

Question 20.
What is isotone? Give an example.
Answer:
Atoms of different elements with different atomic numbers and different mass numbers, but with the same number of neutrons are called isotones.
Example: Pair of elements Boron and Carbon has the same number of neutrons but
different number of protons and hence different atomic numbers.

VII. Answer in detail :

Question 1.
Prove that in the following example, Sulphur and Oxygen combine using the law of reciprocal proportions.
Answer:
Oxygen and sulfur react with copper to give copper oxide and copper sulfide, respectively. Sulphur and oxygen also react with each other to form S02. Therefore,

in CuS ⇒ Cu : S = 63.5 : 32
in CuO ⇒ Cu : O = 63.5 : 16
S : 0 = 32 : 16 ⇒ S:0= 2:1
Now in SO₂:
S : 0 = 32 : 32 ⇒ S: 0 = 1:1
Thus the ratio between the two ratios is 2 : 1
This is a simple multiple ratio.

Question 2.
Explain about radioactive decay and radioactive isotopes.
Answer:
When the nucleus of an atom possesses either too many or too few neutrons compared to the number of protons it becomes unstable. These are called radioactive isotopes. Unstable nuclei split up in a process called radioactive decay and emit radioactive radiation.

Many elements have isotopes of which some of them are radioactive isotopes. There is a lot of low-level natural radioactivity around us. For example, our bodies contain radioisotopes, such as Potassium – 40, which continuously emit radiation, but because the amount is very low this does not harm us. Carbon -14 is a radioactive isotope used to date organic material.

Question 3.
Describe the limitations in Rutherford’s model.
Answer:

• According to electromagnetic theory, a moving electron, accelerate and continuously lose energy.
• Due to the loss of energy, path of the electron may reduce and finally the electron fall into the nucleus.
• If it happens so, atom becomes unstable. But atom are stable. Thus Rutherford’s model failed to explain the stability of an atom.

Question 4.
Explain the electronic configuration of atoms with an illustration.
Ans. Electronic configuration of atoms:

• Electrons occupy different energy levels called orbits or shells.
• The distribution of electrons in these orbits of an atom is governed by certain rules or conditions. These are known as Bohr and Bury Rules of electronic configuration.
• Bohr and Bury simultaneously proposed the following rules for the distribution of electrons in different shells.

Rule 1: The maximum number of electrons that can be accommodated in a shell is equal to 2n² where ‘n’ is the quantum number of the shell (i.e., the serial number of the shell from the nucleus).
Shell Value of (n) Maximum number of electrons (2n2)

Shell	Value of (n)	Maximum number of electrons (2n2)
K	1	2 x 12 = 2
L	2	2 x 22 = 8
M	3	2 x 32 = 18
N	4	2 x 42 = 32

Rule 2: Shells are filled in a stepwise manner in the increasing order of energy.
Rule 3: The outermost shell of an atom cannot have more than 8 electrons even if it has the capacity to accommodate more electrons. For example Electronic configuration in Ca

Illustration:

Question 5.
Explain the valence electron and valency with an illustration.
Answer:

Valence elect runs
How many electrons are in the outermost shell of nitrogen? 5 The outermost shell of an atorh is called its valence shell and the electrons present in the valence shell are known as valence electrons.

The chemical properties of elements are decided by these valance electrons, since they are the ones that take part in chemical reaction.

The elements with same number of electrons in the valence shell show similar properties and those with a different number of valence electrons show different chemical properties. Elements, which have valence electrons 1 ‘ or 2 or 3 (except Hydrogen) are metals.

These elements can lose electrons to form ions which are positive charged and are called cations.

Elements with 4 to 7 electrons in their valence shells are non-metals.
These elements can gain electrons to form ions which are negatively charged and are called anions

VALENCY:

Valency of the element is the combining capacity of the element with other elements and is equal to the number of electrons that take part in a chemical reaction. The valency of the elements having valence electrons 1, 2, 3 is 1, 2, 3 respectively.
While valency of element with 4, 5, 6 & 7 valence electron is 4, 3, 2 and 1 (8 – valence electrons) respectively. Elements having completely filled the outermost shell show Zero valency.

For example The electronic configuration of Neon is 2,8 (completely filled). So valency is 0

Illustration:
Assign the valency of Magnesium & Sulphur.
Electronic configuration of magnesium is 2, 8, 2. So valency is 2.
The electronic configuration of sulphur is 2, 8, 6. So valency is 2 i.e. (8 – 6).

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 5 Magnetism and Electromagnetism Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 5 Magnetism and Electromagnetism

9th Science Guide Magnetism and Electromagnetism Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following converts electrical energy into mechanical energy?
(a) Motor
(b) Battery
(c) Generator
(d) Switch
Answer:
(a) Motor

Question 2.
Transformer works on ………………….
(a) AC only
(b DC only
(c) Both AC and DC
Answer:
(a) AC only

Question 3.
The part of the AC generator that passes the current from the armature coil to theexternal circuit is .
(a) field magnet
(b) split rings
(c) slip rings
(d) brushes
Answer:
d) brushes

Question 4.
The unit of magnetic flux density is
(a) Weber
(b) weber/metre
(c) weber/metre²
(d) weber. metre²
Answer:
(c) weber/metre²

II. Fill in the blanks :

1. The SI Unit of magnetic field induction is ……………..
Answer:
Tesla

2. Devices which is used to convert high alternating current to low alternating current is ………………….
Answer:
transformers

3. An electric motor converts ………………
Answer:
electrical energy into mechanical energy

4. A device for producing electric current is ……………
Answer:
generator

III. Match the following :

1. Magnetic material	a) Oersted
2. Non-magnetic material	b) Iron
3. Current and magnetism	c) Induction
4. Electromagnetic induction	d) Wood
5. Electric generator	e) Faraday

Answer:
1-b, 2-d, 3 -a, 4-e, 5-c

IV. State whether true or false. If false, correct the statement

1. A generator converts mechanical energy into electrical energy.
Answer:
True

2. Magnetic field lines always repel each other and do not intersect.
Answer:
True

3. Fleming’s Left-hand rule is also known as the Dynamo rule.
Answer:
False.
Correct statement: Fleming’s Left-hand rule is also known as the motor rule.

4. The speed of rotation of an electric motor can be increased by decreasing the area of the coil.
Answer:
False.
Correct statement: The speed of rotation of an electric motor can be increased by increasing the area of the coil.

5. A transformer can step up the direct current.
Answer:
False.
Correct statement: A transformer can step up alternating current (AC).

6. In a step-down transformer the number of turns in the primary coil is greater than that of the number of turns in the secondary coil.
Answer:
True.

V. Answer in brief:

Question 1.
State Fleming’s Left Hand Rule.
Answer:
It states that while stretching the three fingers of the left hand in a perpendicular manner with each other if the direction of the current is denoted by the middle finger of the left hand and the second finger is for the direction of the magnetic field then the thumb of the left hand denotes the direction of the force or movement of the conductor.

Question 2.
Define magnetic flux density.
Answer:
The number of magnetic field lines crossing unit area kept normal to the direction of field lines is called magnetic flux density. Its unit is Wb/m²

Question 3.
List the main parts of an electric motor.
Answer:
The main parts of an electric motor are:

1.  Shaft,
2. Primary and Secondary windings,
3. Ball bearings,
4. Armature,
5. Stator,
6. Commutator,
7. Brushes,
8. Terminals

Question 4.
Draw and label the diagram of an AC generator.

PARTS
N, S – Permanent magnet
A B C D – Rectangular coil or armature.
S₁,₂ – Slip rings
B₁, B₂ – Carbon brushes

Question 5.
State the advantages of AC over DC.
Answer:
Advantages of AC over DC:

• • The Voltage of AC can be varied easily using a device called a transformer. The AC can be carried over long distances using step-up transformers. The loss of energy while distributing current in the form of AC is negligible.
  • Direct current cannot be transmitted as such. The AC can be easily converted into DC. Generating AC is easier than DC. The AC can produce electromagnetic induction which is useful in several ways.

Question 6.
Differentiate step up and step down transformer.
Answer:

Step-up transformer	Step down transformer
1. It is a device used to raise the electric voltage (Vs > Vp)	It is designed to reduce the voltage (Vs < Vp).
2. It has more turns on its secondary wind-ing in comparison to the primary one (Ns > Np).	It has fewer turns on the secondary winding (Ns < Np).
3. It is used to start the electrical motor and step-up the windings.	It is used to balance the ratio of voltage and current on the primary and secondary windings.
4. It takes a lot of voltage to initially start the motor turning. It increases the voltage but decreases the current.	The secondary windings have fewer turns which mean low voltage and higher current while it is the opposite in the case of the primary winding.
5. It is found is a television and in power stations.	It is found in laptops and phone chargers.

Question 7.
A portable radio has a built-in transformer so that it can work from the mains instead of batteries. Is this a step up or step down transformer? Give reason.
Answer:
A step-down transformer is used in a portable radio in order to reduce the voltage.

Question 8.
State Faraday’s laws of electromagnetic induction.
Answer:
First law: Whenever there is a change in magnetic flux linked with a coil, an electric current is induced. The induced potential difference lasts so long as there is a change in the magnetic flux linked with the coil.

Second law: The magnitude of the induced current is directly proportional to the rate of change of magnetic flux linked with the coil.

VI. Answer in detail :

Question 1.
Explain the principle, construction, and working of a dc motor.
Answer:
Principle: An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. The direction of force is given by Fleming’s left-hand rule.
Construction: An electric motor consists of the following main parts:

Armature: It is a rectangular coil ABCD having a large number of turns of this insulated copper wire wound over a soft iron core. The armature is placed between the poles of the field magnet and it can be rotated about an axis perpendicular to the magnetic field lines.

Split rings (commutators): It consists of a cylindrical metal ring split into two halves S₁ & S₂ As the coil rotates, the split rings also rotate about the same axis of rotation. The function of the split ring is to reverse the direction of current in the coil after every half rotation.

Carbon brushes: Two graphite or flexible metal rods maintain a sliding contact with split rings S₁and S₂ alternately.

Battery: A battery of few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings.

Working: A simple coil is placed inside two poles of a magnet. Now, look at the current-carrying conductor segment AB. The direction of the current is towards B, whereas in the conductor segment CD the direction is opposite. As the current is flowing in opposite directions in the segments AB and CD, the direction of the motion of the segments would be in opposite directions according to Fleming’s left-hand rule. When two ends of the coil experience force in opposite direction, they rotate.

If the current flow is along the line ABCD, then the coil will rotate in a clockwise direction first and then in an anticlockwise direction. If we want to make the coil rotate in any one direction, say clockwise, then the direction of the current should be along ABCD in the first half of the rotation and along DCBA in the second half of the rotation.

When the gap in the split ring commutator is aligned with terminals X and Y there is no flow of current in the coil. But, as the coil is moving, it continues to move forward bringing one of the split ring commutators in contact with the carbon brushes X and Y. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil.

Question 2.
Explain two types of transformer.
Answer:
Step-up transformer: The transformer used to change a low alternative voltage to a high alternating voltage is called a step-up transformer, ie (V_s > V_p)
In a step-up transformer, the number of turns in the secondary coil is more than the number of turns in the primary coil (N_s >N_p)

Step down transformer: The transformer used to change a high alternating voltage to a low alternating voltage is called a step-down transformer (V_s< V_p). In a step-down transformer, the number of turns in the secondary coils is less than the number of turns in the primary coil (N_s < N_p)

Question 3.
Draw a neat diagram of an AC generator and explain its working.
Answer:

• An alternating current (AC) generator, as shown in, consists of a rotating rectangular coil ABCD called armature placed between the two poles of a permanent magnet.
• The two ends of this coil are connected to two slip rings S₁ and S₂. The inner sides of these rings are insulated.
• Two conducting stationary brushes B₁and B₂ are kept separately on the rings S₁and S₂ respectively.
• The two rings S₁ and S₂ are internally attached to an axle.
• The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the external circuit.
• When the coil is rotated, the magnetic flux linked with the coil changes. This change in magnetic flux will lead to generation of induced current.
• The direction of the induced current, as given by Fleming’s Right Hand Rule, is along ABCD in the coil and in the outer circuit it flows from B₂ to B₁
• During the second half of rotation, the direction of current is along DCBA in the coil and in the outer circuit it flows from B₁ to B₂.
• As the rotation of the coif continues, the induced current in the external circuit is changing its direction for every half a rotation of the coil.

Intext Activities

ACTIVITY – 1

Put a magnet on a table and place some paper clips nearby. If you push the magnet slowly towards the paper clips, there will be a point at which the paper clips jump across and stick to the magnet. What do you understand from this?

Aim :
To study the property of a magnet.

Materials required :
Strong bar magnet, paper clips.

Procedure: Case (i)

• Put a bar magnet on a table and place some paper clips nearby.
• If you push the magnet slowly towards the paper clips, there will be a point at which the paper clips jump across and stick to the magnet. What do you understand from this?

Conclusion :

•  From the above activity, we can conclude that magnets have an invisible field all around them which attracts magnetic materials.
• In this space we can feel the force of attraction or repulsion due to the magnet.
• Thus magnetic field is the region around the magnet where its magnetic influence
  can be felt. It is called a magnetic field.
  [End of the activity]

ACTIVITY – 2

Take a cardboard and thread a wire perpendicular through it. Connect the wire such that current flows up the wire. Switch on the circuit. Let the current flow. Place a magnetic compass on the cardboard and mark the position. Now move the magnet and mark the new position. If you join all the points you will find that it is a circle. Reverse the direction of the current, you will find the magnetic circles are clockwise.

Aim :
To observe the magnetic field around a straight conductor carrying current.

Materials required :
Thick copper wire (conductor), some connecting wires, battery, key, white cardboard, magnetic compass.

Procedure :

• Fix white cardboard horizontally.
• Make a small hole at its centre.
• Pass the thick copper wire through the hole, perpendicular to the cardboard.
• Join the ends of the thick copper wire to a battery and a key with the help of some connecting wires.
• Switch on the circuit. Let the current flow.
• Place a magnetic compass on the cardboard.
• Mark S and N point of the compass X and Y respectively on the cardboard.
• Move the compass such that S end touches Y.
• Now mark the N end as Z In the next step move the compass such that S end touch Z. Repeat the steps. .
• Now join all the points. What do you observe?
• Now keep the compass away from the centre and follow.

Observation:

• It is seen that it is a circle.
• We can draw another magnetic line and the magnetic lines are concentric circles and also we will find the magnetic lines are anti-clockwise.
• When the direction of current is reversed, the direction of magnetic lines of force
  are clockwise.

[End of the activity]

ACTIVITY – 3

Create your own electromagnet
You are given a long iron nail, insulation coated copper wire, and a battery. Can you make your own electromagnet?

Aim :
To create your own electromagnet.

Materials required :
Iron nail insulated coated copped wire, battery, and paper clips.

Procedure :

• Take an iron nail, wind ten or more loops of insulated copper wire around it. However, make sure not to make the diameter of the loop more than a centimetre in width.
• Connect the ends of the wire to a key and a battery.
• Switch on the key and bring some paper clips close to the nail.
• Switch off the key. What do you observe?

Observation :
When the key is switched on, the electromagnet attracts the paper clips due to the current flowing through the coil wound around the iron nail. When the key is switched off, the paper clips detach from the iron nail

Conclusion:
Thus an electromagnet is a temporary magnet which behaves as a magnet in the presence of an electric current.

9th Science Guide Magnetism and Electromagnetism Additional Important Questions and Answers

Choose the correct answer:

Question 1.
The direction of the magnetic field around a straight conductor carrying current can be determined by …………………
(a) Fleming’s left-hand rule
(b) Lenz’s law
(e) Right-hand thumb rule
(d) Fleming’s right-hand rule
Answer:
(a) Fleming’s left-hand rule

Question 2.
The magnetic field produced due to a circular wire at its centre is _______.
(a) at 45° to the plane of the wire
(b) at 60° to the plane of the wire
(c) in the plane of the wire
(d) perpendicular to the plane of the wire
Answer:
(d) perpendicular to the plane of the wire

Question 3.
A magnetic field exerts no force on ………………
(a) stationary electric charge
(b) a magnet
(e) an electric charge moving perpendicular to its direction
(d) an unmagnetized iron bar.
Answer:
(a) stationary electric charge

Question 4.
At the centre of a magnet, the magnetism is ______ .-
(a) zero
(b) same as the poles
(c) maximum
(d) minimum
Answer:
(a) zero

Question 5.
Induced current flows through a coil ______.
(a) more than the period during which flux changes through it.
(b) less than the period during which flux changes through it
(c) only for the period during which flux changes through it
(d) None of the above
Answer:
c) only for the period during which flux changes through it

Question 6.
Which of the following instruments works by electromagnet-ic induction?
(a) dynamo
(b) moving coil galvanometer
(c) telephone receiver
(d) simple motor
Answer:
(a) dynamo

Question 7.
For making a strong electromagnet the material of the core should be_______.
(a) brass
(b) laminated steel strips
(c) soft iron
(d) steel
Answer:
(c) soft iron

Question 8.
Magnetic field lines determine ______
(a) the shape of the magnetic field
(b) only the direction of the magnetic field
(c) only the relative strength of the magnetic field
(d) both the direction and the relative strength of the magnetic field
Answer:
(d) both the direction and the relative strength of the magnetic field

Question 9.
A magnetic needle is kept in a non-uniform magnetic field. It experiences …………….
(a) a force and a torque
(b) a force but not a torque
(c) a torque but not a force
(d) neither a force nor a torque
Answer:
(a) a force and a torque

Question 10.
The most suitable material for making permanent magnets is ………………..
(a) copper
(b) aluminum
(c) iron
(d) steel
Answer:
(d) steel

Question 11.
An electric generator converts
(a) electrical energy into mechanical energy
(b) mechanical energy into heat energy
(e) electrical energy into electrical energy
(d) mechanical energy into electrical energy
Answer:
(d) mechanical energy into electrical energy

II. Fill in the blanks:

1. The magnetic field inside a _____ is uniform.

Answer:
magnet

2. An AC generator is provided with …………… slip rings which rotate with the coil.
Answer:
two

3. The moving part of an electric motor is called ……………
Answer:
shaft

4. A magnetic field is a ………………….quantity
Answer:
Vector

5. The SI unit of magnetic field strength is ……………………
Answer:
Tesla

6. The laws of induction were given by ________
Answer:
Faraday

7. The relation between weber and Tesla is________
Answer:
1wb = 1T × 1m²

8. Unlike magnetic poles ________whereas like poles ________
Answer:
attract, repel

9. Magnetic lines of force never ______ each other.
Answer:
intersect

10. Sailors use ………………. to find direction in order to navigate on the sea.
Answer:
Magnetic compass

11. The strongest natural magnet is ………………….
Answer:
lodestone magnetite

12. The ______ produces its own magnetic field, which shields the earth’s ozone layer from the …………… and is important in navigation.
Answer:
Earth, solar wind

13. Sea turtles return to their birth beach many decades after they were born due to ……………..
Answer:
geomagnetic imprinting

14. Magnetic field at a point is ………………. to the magnetic field lines.
Answer:
tangential

15. ……………… is the number of magnetic field lines passing through a given area.
Answer:
Magnetic flux

16. The direction of the magnetic lines around a current-carrying conductor can be easily
understood using the ………….. rule.
Answer:
right-hand thumb rule

17. The magnetic field lines are stronger near the ……………… and it diminishes as you go away from it.
Answer:
current-carrying wire

18. A charge moving in a magnetic field, in a direction other than the direction of the magnetic field, experiences a force. It is called the ………………. force.
Answer :
magnetic Lorentz

19. When the conductor is perpendicular to the magnetic field, the force will be the …………….., When it is parallel to the magnetic field, the force will be ………………..
Answer:
maximum, zero

20. An electric bell contains an …………………., consisting of coils of insulated wire wound around
iron rods.
Answer:
electro magnet

21 . No force acts in a current carrying conductor when it is to the magnetic
field.
Answer: parallel

III. Match the following :

Question 1.

1. Electric generator	a) Electro magnetic induction
2. Dynamo	b) Fleming’s left hand rule
3. Magnetic field lines	c) Slip rings
4. Electric motor	d) North to south

.Answer:
1-c, 2 -a, 3-d, 4-b

Question 2.

1. Electricity and magnetism	a) Step-down transformer
2. Force on the conductor	b) Hans Christian Oersted
3. Electric bell	c) I L B
4. Ns <Np	d) Electromagnet

Answer:
1-b, 2-c, 3-d, 4-a

IV. State whether true or false. If false, correct the statement:

1. Fleming’s left-hand rule is also known as the dynamo rule.
Answer:
False.
Correct statement: Fleming’s right-hand rule is also known as the dynamo rule.

2. Magnetic field lines always repel each other and do not intersect.
Answer:
True.

3. A current flowing in a wire gives rise to a magnetic field.
Answer:
True.

4. The magnetic field lines due to a straight wire carrying current are parallel.
Answer:
False.
Correct statement: The magnetic field lines due to a straight wire carrying current are concentric circles.

5. A generator converts mechanical energy into electrical energy.
Answer:
True.

6. The magnetic field is a quantity that has magnitude only.
Answer:
False
Correct statement: The magnetic field is a quantity that has magnitude and direction

7. Magnetic fields do not interact with electric charges in motion.
Answer:
False.
Correct statement: Magnetic fields do not interact with electric charges at rest.

8. The force on a charged particle is moving in a magnetic field is maximum when the angle between the direction of motion and field is 90°.
Answer:
True.

9. An electric motor converts mechanical energy into electrical energy.
Answer:
False.
Correct statement: An electric motor converts electrical energy into mechanical energy.

10. The field at the centre of the long circular coil carrying current will be parallel straight lines.
Answer:
True.

11. A wire with green insulation is usually the live wire of an electric supply.
Answer:
False
Correct statement: A wire with green insulation is usually the earth wire of an electric supply.

12. An electric generator works on the principle of electromagnetic induction.
Answer:
True.

13. Permanent magnets are made of hard magnetic materials like alnico.
Answer:
True.

14. The pole of a freely suspended magnet which points towards the north is called the south pole and what points towards south is celled north pole.
Answer:
False.
Correct statement: The pole of a freely suspended magnet that points towards the north is called the north pole and that points towards the south are called a south pole.

15. The magnetic poles always exist in pairs.
Answer:
True

16. A galvanometer is an instrument that can detect the presence of a current is a circuit.
Answer:
True

V. Assertion and Reason type questions :

Mark the correct choice as:
(a) If both assertion and reason are true and the reason is the correct explanation of assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true

Question 1.
Assertion (A): When 2 long parallel wires, hanging freely are connected in parallel to a battery, they come closer to each other.
Reason (R): Wires carrying current in opposite direction repel each other.
Answer :
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion

Reason: The wires are parallel to each other but the direction of current in it is in the same direction, so they attract each other. If the current in the wire is in opposite direction then wires repel each other.

Question 2.
Assertion (A) : The work done by a magnetic field on moving charge is zero.
Reason (R) : In a magnetic field force is perpendicular to the velocity.
Answer:
(a) Both assertion and reason are true and the reason is the correct explanation of

Question 3.
Assertion (A): A current-carrying conductor experiences a force in a magnetic field.
Reason (R): The net charge on a current-carrying conductor is zero.
Answer:
(b) Assertion and reason are true but the reason is not the correct explanation of the assertion

Reason: When a current-carrying conductor having no net charge is placed in a magnetic field, the free electrons of the conductor move towards the positive end of the conductor with the same drift velocity, hence magnetic force acts on them; The positive ions of the conductor being stationary, do not experience any magnetic field.

Question 4.
Assertion (A) : A magnetic field exerts a force on a moving charge in the same direction as the direction of the field itself.
Reason (R) : The direction of force is given by Fleming’s left-hand rule.
Answer :
(d) Assertion is false but the reason is true
Reason: According to Fleming’s left-Hand Rule, the direction of the magnetic force on a moving charge is always perpendicular to the magnetic field.

VI. Define the following :

Question 1.
Define the terms magnet and magnetism.
Answer
The substances which have the property of attracting small pieces of iron, nickel, cobalt, etc, are called magnets, and this property of attraction is called magnetism.

Question 2.
Define natural magnet.
Answer:
It is a piece of lodestone, which is a black iron oxide (Fe₃ O₄) called magnetite. The word lodestone means a leading stone.

Question 3.
Define artificial magnet.
Answer:
Pieces of iron and other magnetic materials which can be made to acquire the properties of natural magnets are called artificial magnets.

Question 4.
Define magnetic field.
Answer:
The region around a magnet within which its influence can be experienced is called a magnetic field.

Question 5.
Define magnetic field lines of force.
Answer:
The path in a magnetic field in which a unit north pole tends to move when allowed to do so is known as magnetic field lines of force.

Question 6.
Define magnetic flux.
Answer:
Magnetic flux is the number of magnetic field lines passing through a given area. It is denoted by (Φ) and its unit is weber (Wb).

Question 7.
Define magnetic shielding.
Answer:
The process of stopping the magnetic field from entering into a region is called magnetic shielding.

Question 8.
Define magnetic effect of electric current.
Answer:
A current-carrying conductor is always associated with a magnetic field around it is called the magnetic effect of current. It was first discovered by Hans Christian Oersted in 1820.

Question 9.
Define the right-hand thumb rule.
Answer:
If the current-carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

Question 10.
Define Fleming’s Left Hand Rule.
Answer:
The law states that while stretching the three fingers of the left hand in a perpendicular manner with each other if the direction of the current is denoted by the middle finger of the left hand and the second finger is for the direction of the magnetic field then the thumb of the left hand denotes the direction of the force or movement of the conductor.

Question 11.
Define electromagnet.
Answer:
lt is a solenoid with a soft iron core placed inside it. When current is passed through the solenoid, the soft iron core becomes a temporary magnet.

Question 12.
Define electric motor.
Answer:
lt is a device to convert electrical energy into mechanical energy. It is based on the principle that when a current-carrying coil is placed in a magnetic field, it experiences a force.

Question 13.
Define electromagnetic induction.
Answer:
Whenever the magnetic lines of force passing through a closed-circuit change, a voltage and hence a current is induced in it. This phenomenon is called electromagnetic r induction. It was discovered by Michael Faraday in 1831.

Question 14.
Define Fleming’s Right Hand Rule.
Answer:
Stretch the thumb, forefinger, and middle finger of your right hand mutually perpendicular to each other. If the fore finger indicates the direction of the magnetic field and the thumb indicates the direction of motion of the conductor, then the middle finger will indicate the direction of the induced current. Fleming’s Right-hand rule is also called the “generator rule”.

Question 15.
Define an electric generator or a dynamo.
Answer:
lt is a device to convert mechanical energy into electrical energy. It is based on the principle of electromagnetic induction that a current is induced in a closed circuit when the magnetic field passing through it changes.

Question 16.
Define a Transformer.
Answer:
The transformer is a device used for converting low voltage into high voltage and high voltage into low voltage. It works on the principle of electromagnetic induction.

Question 17.
Define step up and step down transformer.
Answer:
Step-up transformer: The transformer used to change a low alternating voltage to a high alternating voltage is called a step-up transformer, (ie) (V_s > V_p).
Step down transformer: The transformer used to change a high alternating voltage to a low alternating voltage is called a step-down transformer (V_s < V_p).

VII. Answer in brief :
Question 1.
Mention the properties of magnetic lines of force.
Answer:
Magnetic lines of force are closed continuous curves, extending through the body of the magnet.
Magnetic lines of force start from the North Pole and end at the South Pole.

Question 2.
Give the uses of magnets in everyday life.
Answer:

•  Used in radio and stereo speakers
• Used in almirah and refrigerator doors to snap them closed.
• In medicine, magnetic resonance imaging (MRI) scanners expose the inner parts of the patient’s body for detailed examination by doctors.

Question 3.
Can two magnetic lines of force intersect? Justify your answer:
Answer:
No, if two magnetic lines of force intersect then there will be two tangents and hence two directions of the magnetic field at the point of intersection. This is not possible.

Question 4.
Why does a compass needle get deflected when brought near a bar magnet?
Answer:
The magnetic field of the magnet exerts a force on both the poles of the compass needle. The forces experienced by the two poles are equal and opposite. These two forces form a couple which deflects the compass needle.

Question 5.
Draw magnetic field lines around a bar magnet.
Answer:

Question 6.
Give some uses of electromagnets.
Answer:

• It is used in factories and cranes to lift heavy iron ingots and steel, scraps from one place to another.
• Used in hospitals to remove iron splinters from the eyes of the patients.
• Used in electric bells, relays, electric switches etc.

Question 7.
Two coils A and B of insulated wire are kept close to each other. Coil A is connected to a galvanometer. While coil B is connected to a battery through a key. What would happen if.
(i) a current is passed through coil B by plugging the key?
(ii) the current is stopped by removing the plug from the key?
Answer:
(i) If a current is passed through coil B by plugging the key, the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil – A (As the current in coil B changes, the magnetic field associated with it also changes).

(ii) If the current is stopped by removing the plug from the key :
The needle of the galvanometer in coil – A momentarily moves but to the opposite side. It means that now the current flows in the opposite direction in coil – A.

VIII. Answer in detail

Question 1.
Explain the principle, construction, and working of an AC generator.
Answer:

• An alternating current (AC) generator, consists of a rotating rectangular coil ABCD called armature placed between the two poles of a permanent magnet.
• The two ends of this coil are connected to the two slip rings S₁ and S₂. The inner sides of these rings are insulated.
• Two conducting stationary brushes B₁ and B₂ are kept separately on the rings S₁ and S₂ respectively. The two rings S₁ and S₂ are internally attached to an axle.
• The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two bushes are connected to the external circuit.
  When the coil is rotated, the magnetic flux linked with the coil changes. This change in magnetic flux will lead to generation of induced current.
• The direction of the induced current, as given by Fleming’s Right Hand Rule, is along ABCD in the coil and in the outer circuit it flows from
  B₂ to B₁
• During the second half of rotation, the direction of current is along DCBA in the coil and in the outer circuit it flows from B₁ , to B₂
• As the rotation of the coil continues, the induced current in the external circuit is changing its direction for every half a rotation of the coil.

Question 2.
Explain the working of following devices.
(i) Speaker
(ii) Magnetic levitation trains.
Answer:
(i) Inside the speaker, the electromagnet is placed in front of a permanent magnet. The permanent magnet is fixed firmly in position whereas the electromagnet is mobile. As pulses of electricity pass through the coil of the electromagnet, the direction of its magnetic field is rapidly changed. This means that it is, in turn, attracted to and repelled from the permanent magnet vibrating back and forth. The electromagnet is attached to a cone made of a flexible material such as paper or plastic which amplifies these vibrations, pumping sound waves into the surrounding air towards our ears.

(ii) Magnetic levitation (Maglev) is a method by which an object is suspended with no support other than magnetic fields. In Maglev trains two sets of magnets are used, one set to repel and push the train up off the track,’ then another set to move the floating train ahead at great speed without friction. In this technology, there is no moving part. The train travels along a guide way of magnets which controls the train’s stability and speed using the basic principles of magnets.

Question 3.
Explain the application of electromagnets in the field of medical system.
Answer:
Nowadays electromagnetic fields play a key role in advanced medical equipment such as hyperthermia treatments for cancer, implants and magnetic resonance imaging (MRI). In a, sophisticated equipments working based on electromagnetism can scan minute details of the human body.

Many of the medical equipments such as scanners, X-ray equipments and other equipments also use principle of electromagnetism for their functioning

Question 4.
Explain the properties of magnetic lines of force.
Answer:

• Magnetic lines of force are closed, continuous curves, extending through the body of the magnet.
• Magnetic lines of force start from the North Pole and end at the South Pole.
• Magnetic lines of force never intersect.
• They will be maximum at the poles than at the equator.
• The tangent drawn at any point on the curved line gives the direction of the magnetic field.

IX. Numerical Problems:

Question 1.
A 0.4 m wire, stretched horizontally, carries an electric current of 15 A, in a magnetic field whose magnetic field intensity is 0.1 N/Am. What is the magnitude on the wire?
Given: l = 0.4 m, I = 15A
Magnetic induction B = 0.1 N/Am
Solution:
Force to be used F = B I l
= 0.1 × 15 × 0.4
F = 0.6N

Question 2.
A wire 10 cm long carrying a current of 1.5 A is held in a uniform magneÑic field in which B = 10^-3 T. Calculate the force on the wire if it is held perpendicular to the lines of the magnetic field.
Given : Length of the wire l = 10 cm = 0.10 m
Current I= 1.5 A
Magnetic induction B = 10^-3T
Solution:
ForceF = B I l
= 10^-3 × 1.5 × 0.10
= 1.5 × 10^-3 N.

Question 3.
A conductor of length 50 cm carrying a current of 5 A is placed perpendicular to a magnetic field of induction 2×10 ^-3T. Find the force on the conductor.
Solution :
Force on the conductor = ILB
= 5 × 50 × 10^-2 × 2 × 10^-3
= 5 × 10^-3

Question 4.
A current-carrying conductor of a certain length, kept perpendicular to the magnetic field experiences a force F. What will be the force if the current is increased four times, the length is halved and the magnetic field is tripled?
Solution :
F = I L B = (4I) × \(\left(\frac{L}{2}\right)\) × (3 B) =6 F
Therefore, the force increases six times.

Question 5.
The primary coil of a transformer has 800 turns and the secondary coil has 8 turns. It is connected to a 220 V ac supply. What will be the output voltage?
Solution: