Question

A black body of temperature $T$ is inside the chamber of $T_0$ temperature initially. Sun rays are allowed to fall from a hole in the top of the chamber. If the temperatures of black body $\left(T\right)$ and chamber $\left(T_0\right)$ remain constant, then

• A. The rate of emission of energy from the black body remains the same
• B. The rate of emission of energy from the black body increases
• C. The rate of absorption of energy by the black body increases.
• D. The energy radiated by the black body equals the energy absorbed by it

Answer 1

Answer: (A), (D)

The correct options are
A The rate of emission of energy from the black body remains the same
D The energy radiated by the black body equals the energy absorbed by it

It is given that the absolute temperatures of both the black body and the surroundings are constant with time, even after sunlight(radiation) is incident on it.

• When a body absorbs radiation, its temperature increases
• When a body emits radiation, its temperature decreases

Also the sun, being a source of infinite radiation(very large source of radiation).
We infer from this that the incident radiation should be of constant magnitude.
And if the temperature of the black body is a constant, that means it's emission and absorption of radiation are matched and equal. The absorption is of constant magnitude, because the sun's radiation is of constant value. Hence the emission is of constant value also and is equal to the absorption.