Question

Absorptive power of a perfectly black body and white body is:
-1,1
0,1
1,1
1,0

Answer 1

Hint :The absorptive power of a body or a surface is defined as the ratio of the energy absorbed in a given time to the radiant energy absorbed in a given time to the radiant energy incident on it at the same instant of time .
The absorptive power of a black body is 1 because it absorbs all wavelengths incident on it.
Absorptive power of a white body is 0.

Complete step by step solution:
A black body is an object with emissivity $ = 1$ that absorbs as well as it emits. It absorbs and emits according to Stephen- Boltzman (the total energy radiated per unit surface area of a black body across all wavelength per unit time ) law until equilibrium (here equilibrium is thermal equilibrium where temperature remains constant ) is reached .In thermal equilibrium blackbody emits electromagnetic radiation according to planck's law ,which means that it has a spectrum that is determined by the temperature alone, not by the body’s shape or composition.

On the contrary ,white body has a surface that absorbs no electromagnetic radiation of any wavelength ,that is one which exhibits zero absorptivity for all wavelengths.

We can better understand the above question by an example .
Suppose two cars one is having black colour and the other is having white colour are allowed to stand in the sun for 10 hrs . After 10hrs if we check the temperature of both the cars from inside ,we found that black cars have far higher temperatures than white cars because black cars absorb the maximum heat from sunlight as compared to white cars.

Therefore our answer is :

So, correct Option is 4.

Note:
Emissive power :The energy of thermal radiation emitted in all directions per unit time from each unit area of surface at any given temperature.
if Q is the amount of radiant energy emitted ,A is the surface area of the body and t is the time for which the body radiates energy ,then emissive power is
$E = \dfrac{Q}{{At}}$