Question

Good absorbers of heat are:
$\left( A \right)$ poor emitters
$\left( B \right)$ non – emitters
$\left( C \right)$ good emitters
$\left( D \right)$ highly polished

Answer 1

Hint:- We will start this question by choosing the right option and then by taking the help of a law we will prove it and then we will also give some other reasons to prove it and this will easily give us the required answer.

Complete step-by-step solution -

We know that,
Poor emitters are not good absorbers of heat and non – emitters are also not good absorbers of heat.
Also, highly polished surfaces are poor emitters of heat but are not good absorbers of heat.

The good absorbers of heat are good – emitters of heat and are based on Kirchhoff’s radiation law.
According to Kirchhoff’s law, a body strongly absorbs a radiation of certain wavelength, it must emit strongly the radiation of the same wavelength.

Other reasons of good – emitters of being good absorbers of heat:
1. When we give heat energy to a substance the molecules of that substance get excited due to excessive amounts of energy inputs.
2. Now, the good absorbers of the heat energy will absorb a great amount of heat energy which will make the molecules of that substance excited in more amounts.
3. Now, the molecules will surely want to expel that extra amount of energy to become a stable molecule.
4. Now, this expelled amount of energy or the emitting amount of heat energy will be directly proportional with the absorbed energy.
5. That’s why the substances which are good absorbers are good emitters also.
Therefore, option $C$ is the right answer.

Note – Absorptance is defined as the ratio of the amount of thermal energy absorbed by a body in a certain time to the total amount of thermal energy incident upon the body at the same time. Transmittance is defined as the ratio of the amount of thermal energy transmitted by a body in a certain time to the total amount of thermal radiation incident on it at the same time.