Q2 of 11 Page 134

Who is telling lies?

(a) Light year is used to measure time


(b) End stage of a star depends on its initial mass


(c) A star ends its life as a neutron star when the pressure of its electrons balances its gravity


(d) Only light can emit from the black hole


(e) The Sun will pass through the supergiant stage during its evolution


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

(a)Lie

Explanation:


This is a lie because light year is used to measure distance.


1 light year = Distance travelled by light in one year


1 light year = km


(b) No Lie


Explanation:


Yes, the end stage of star depends on its initial mass.


Now, we are using mass of Sun = as a unit of measurement of mass of stars. So, the following table shows the end stage depends on the initial mass.


= Mass of Star



(c) Lie


Explanation:


A star ends up its life as a neutron star when the pressure of its neutrons (and not the electron) balances its gravity. The pressure of these neutrons is independent of temperature and balances the gravitational force forever.


(d) Lie


Explanation:


This is a lie since the black hole does not emit and it absorbs any light. Any light falling on black hole does not get reflected and gets absorbed inside the star.


(e) Lie


Explanation:


Sun does not pass through the supergiant stage during its evolution. Sun passes through the red giant stage, then explode and then the end stage is a white dwarf. The evolution depends on mass. Only stars having masses greater than the 8 times the mass of Sun undergo a supergiant stage ().


(f) Not Lie


Explanation:


The Sun will end its life as a white dwarf since according to the mass, it will undergo the evolution whose end product is a white dwarf ( is evidently less than 8 ). The White Dwarf is of the size of the earth but has large mass, and thus is highly dense.


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