Question

Which statement is incorrect about ‘White Dwarf’ ?
A. A white dwarf is very dense
B. Its mass is comparable to that of the sun
C. A white dwarf’s faint luminosity come from the emission of stored thermal energy
D. Fusion takes place in a white dwarf wherein mass is converted to energy

Answer 1

Hint: In order to solve this question, we should know that white dwarf is a star which is formed at the stage when it burned its whole hydrogen fuel in nuclear fusion and here we will discuss some basic properties of a white dwarf star and later figure out which of the given statement is incorrect about white dwarf star.

Complete answer:
A white dwarf is a star which comprises mostly helium, carbon and oxygen nuclei which are present in high energetic electrons and the high pressure of these highly energetic electrons prevents the white dwarf star from further collapsing and this structure is known as white dwarf star.

Some of the basic properties of white dwarf stars are listed according to the four statements listed in options are listed as: a white dwarf is very dense as a general white dwarf has a density of $2,00,000$ times that of earth so this statement is correct. A white dwarf mass is generally eight times less than that of our sun hence its mass is comparable to that of the sun. So, this is also a correct statement.

A white dwarf’s faint luminosity comes from the emission of stored thermal energy, this is also the correct statement because the whole thermal energy is used to emit light in white dwarf star.Fusion takes place in a white dwarf wherein mass is converted to energy, this is a wrong statement because once a white dwarf star is formed no more fusion takes place inside it as it burns all of its hydrogen fuel already.

Hence, the correct option is D.

Note: It should be remembered that, a white dwarf is stable only due to presence of highly energetic electrons and their high pressure and final stage of white dwarf is such that after billions of years it cools down and later emit no light from it and then it’s called a black dwarf.