General Science Question Ans Ch 19 Class 8 Maharashtra Board

Exercise

1. Search and you will find.

(a) Our galaxy is called Milky Way.

(b) For measuring large distances, light year is used as a unit.

(d) There are about 100 billion (10¹¹) stars in our galaxy.

(e) The end stage of the Sun will be a white dwarf.

(f) Stars are born out of interstellar clouds.

(g) Milky Way is a spiral galaxy.

(h) Stars are spheres of hot gas.

(i) The masses of other stars are measured relative to the mass of the Sun.

(j) Light takes 8 minutes to reach us from the Sun while it takes 1 second to reach us from the Moon.

(k) The larger the mass of a star, the faster is its evolution.

(l) The number of fuels used in the life of a star depends on its mass.

2. Who is telling lies?

(a) False – A light year is a unit of distance, not time.

(b) True – A star’s end stage depends on its initial mass.

(c) False – A neutron star is formed when the pressure of neutrons balances gravity, not electrons.

(d) False – A black hole does not emit light, it absorbs everything, including light.

(e) False – The Sun will pass through the red giant stage, not the supergiant stage.

(f) True – The Sun will end its life as a white dwarf.

3. Answer the following questions:

(a) How are stars formed?

Stars form from huge clouds of gas and dust in space, called interstellar clouds.
Gravity pulls the gas and dust together, increasing temperature and pressure.
When the core gets hot enough, nuclear fusion starts, and a new star is born.

(b) Why do stars evolve?

Stars evolve because they use up their fuel over time.
As the fuel decreases, the balance between gravity and gas pressure changes.
This leads to different stages like red giant, supergiant, white dwarf, or black hole.

(c) What are the three end stages of stars?

White dwarf: Forms when a small or medium star (like the Sun) runs out of fuel.
Neutron star: Forms when a large star (8 to 25 times the Sun’s mass) explodes as a supernova.
Black hole: Forms when a very massive star (more than 25 times the Sun’s mass) collapses completely.

(d) Why is a black hole called a “black hole”?

A black hole is called so because it has extreme gravity, which pulls in everything, even light.
Since no light escapes, it looks completely black and cannot be seen directly.

(e) Which types of stars end their life as neutron stars?

Stars 8 to 25 times the mass of the Sun end their life as neutron stars.
After a supernova explosion, the remaining core contracts into a dense neutron star.

4. A. If you are the Sun, write about your properties in your own words. B. Describe white dwarfs.

(A) If you were the Sun, what would you write about yourself?

I am the Sun, a medium-sized star at the center of the Solar System.
My energy comes from nuclear fusion, converting hydrogen into helium.
I provide light, heat, and energy to all planets, making life possible on Earth.

(B) Write a short note on white dwarfs.

A white dwarf is the final stage of a low or medium-mass star like the Sun.
It is small, dense, and very hot, but gradually cools over billions of years.
The Sun will eventually become a white dwarf after passing through the red giant stage.