Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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:

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

IV. Answer briefly :

Question 1.
What is solar system?
Answer:

  • The Sun and celestial bodies which revolve around it form the solar system.
  • It consists of larger 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”.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 3.
Define time period of a satellite.
Answer:
Time taken by the satellite to complete one revolution round the Earth is called time period of a satellite.
Time period, T = \(\frac{\text { Distance covered }}{\text { Orbital velocity }}\)

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

  1.  Natural satellites,
  2.  Man made satellites.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 5.
Write a note on the inner planets.
Answer:

  •  The planet that are relatively close together and close to the sun. They form the inner solar system and are called inner planets.
  • There are four inner planets namely
    1. Mercury, 2. Venus, 3. Earth and 4. Mars.
  • They have a surface of solid rock crust and are called terrestial (or) rocky 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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 7.
State Kepler’s laws.
Answer:
Kepler’s first law – the law of ellipses
The path of the planets about the Sun is elliptical in shape, with the centre of Sun being located at one of the foci.

Second law – the law of equal areas.
An imaginary line drawn from the centre of the Sun to the centre of the Planet will sweep out equal areas in equal intervals of time.

Third law – the law of Harmonics.
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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

V. Answer in detail :

Question 1.
Give an account of all the planets in the solar system.
Answer:
1. Mercury:

  • It is a Rocky planet nearest to the Sun.
  • It moves around the Sun faster than any other planet.
  • It rotates very slowly.

2. Venus :

  • It is almost the same size as the Earth.
  • It is the Hottest planet in our solar system.
  • It is brightest heavenly body in our night sky.
  • It spins in the opposite direction to all other planets.

3. The Earth :

  • The only Life-Supporting planet in the solar system.
  • It appears Bluish green due to the reflection of light from water and land mass on its surface.
  • It moves around the Sun in 365.25 days and rotation period is 23.93 hours.

4. Mars :

  • The first planet outside the orbit of the Earth.
  • It is also called the Red Planet having two small natural satellites.

5. Jupiter:

  • Jupiter is called as Giant planet.
  • It is the largest of all planets.
  • It has 3 rings and 65 moons.
  • Its moon Ganymede is the largest moon of our solar system.

6. Saturn:

  • It has bright shiny rings and appears yellowish in colour.
  • It is the second biggest and a giant gas planet in the outer solar system.

7. Uranus:

  • It is a cold gas giant and can be seen only with the help of large telescope.
  • It has longest summers and winters.

8. Neptune:

  • It appears as Greenish star and is the windiest plant.
  • It has the largest moon – Triton that moves in opposite direction to the direction in which its planet spins.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 development of improved vaccines, breast cancer detection and treatment and so on.

Question 3.
Write a note on orbital velocity.
Answer:
Definition of orbital velocity :
The horizontal velocity that has to be imparted to a statellite at the determined height so that it makes a circular orbit around the planet.

  1. The orbital velocity of the satellite depends on its altitude above the Earth.
  2. Nearer the object to the earth, faster is the required orbital velocity.
  3. At an altitude of 200 km, the required orbital velocity is little more than 27,400 kph.

Geostationary orbit:
Satellite stays in a fixed position all the time while earth rotates. This kind of orbit is called geostationary.

Orbital velocity formula : \(v=\sqrt{\frac{\mathrm{GM}}{(\mathrm{R}+h)}}\)
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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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:

  1. The satellite is carried by a rocket to the desired height and released horizontally with a high velocity.
  2. So that it remains moving in a nearly circular orbit

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 in the Earth will weigh 1680 kg in the Sun. Why?
Answer:

  1. Weight of the object depends upon the gravity of the planet.
  2. The gravity of the sun is 28 times higher than the Earth.
  3. So an object with 60 kg in the Earth will weigh 1680 kg (28×60 = 1680 kg) in the Sun.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 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.
Samacheer Kalvi 9th Science Guide Chapter 9 Universe 1
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.
Samacheer Kalvi 9th Science Guide Chapter 9 Universe 2
Intext Activities

ACTIVITY – 1

Form a team of three to four students. Prepare a poster about the astronomers

Samacheer Kalvi 9th Science Guide Chapter 9 Universe 3

[End of the activity]

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

[End of the activity]

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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.
[End of the activity]

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

ACTIVITY – 4

Prepare a list of Indian satellites from Aryabhatta to the latest along with their purposes.
S.No. Name of satellite Year Purpose
E:\jyothi\images\2\Samacheer Kalvi 9th Science Guide Chapter 9 Universe 4.pngs

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 same
(d) a & b
Answer:
(a) increases

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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.
Hottest planet on the solar system is ……………….
(a) Venus
(b) Mercury
(c) Mars
(d) Earth
Answer:
(a) Venus

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 14.
The planet having longest summers and winters is ………………….
(a) Saturn
(b) Neptune
(c) Uranus
(d) Jupiter
Answewr:
(c) Uranus

Question 15.
Windiest planet in the solar system ………………..
(a) Neptune
(b) Uranus
(c) Saturn
(d) Jupiter
Answer:
a) Neptune

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 velcoity of the satellite depends on its ……………………
(a) Shape of orbit
(b) altitude
(c) distance
(d) All of these
Answer:
(b) altitude

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 20.
The time 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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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)

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 star depends on their _______ and _____ from the earth.
Answer:
Intensity and distance

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 planetsi

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 the of
their semi major axis from the Sun.
Answer :
squares, cubes

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

(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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

1. The basic constituent of the universe is luminous matter.
Answer:
True.

2. The important thing about universe is that it is currently shrinking.
Answer:
False.
Correct statement : The important thing about universe is that it is currently expanding.

3. All the matter in the universe is made up of hydrogen and helium.
Answer:
True.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 sun near the poles takes around 25.4 days.
Answer:False.
Correct statement: The rotation of Sun near the poles takes around 36 days.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 southern hemisphere.
Answer:
True.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 as that between Earth and Mars.
Answer:
False.
Correct statement: The distance between Saturn and Uranus is about 20 times as that between Earth and Mars.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 reason is not the correct explanation of assertion

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 amount and have very dense atmosphere.
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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 5.
Assertion : At 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 a 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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

VII. Answer briefly :

Question 1.
Write notes on 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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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 constellation.
  2. They represent an animal, mythological person or creature or an object.
  3. Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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. Half a million pieces of rocks that were left over when the planets were formed are called Asteroids.
  1. Asteroids revolve around the Sun.
  2. Asteroids can only be seen through large telescope.
  3. The biggest asteriod is Ceres.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

VIII. Answer In detail:

Question 1.
Explain the salient features of Iig Bang Theory.
Answer:
According to Big Bang Theory,

  1. The universe was a hot dense matter.
  2. 13.7 billion years ago, an explosion occurred.
  3. All the matter are 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 throghout the Universe.

Question 2.
How is Sun formed according to Big Bang theory?
Answer:
According to 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. Excessive and high speed spinning of cloud results in flattening into giant disc.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

Question 3.
Give a comparative account of satellites and rings of planets.
Answer:
Samacheer Kalvi 9th Science Guide Chapter 9 Universe 5

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 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.

Samacheer Kalvi 9th Science Guide Chapter 9 Universe

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
Samacheer Kalvi 9th Science Guide Chapter 9 Universe 6
Samacheer Kalvi 9th Science Guide Chapter 9 Universe 7
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
Samacheer Kalvi 9th Science Guide Chapter 9 Universe 8

Period of Revolution T = 5.9 15 × 1O 3s
= 5915 sec. (or) 98 min 35 sec.

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