Chapter 22, Problem 13A

Which will normally cool faster, a black pot of hot tea or a silvered pot of hot tea?

To determine

To Explain: The pot which will cool faster.

Answer to Problem 13A

The black pot will cool faster.

Explanation of Solution

Introduction:

When the bodies are in thermal equilibrium, the ratio of emissive power and absorption are same which emit and absorb thermal radiation.

Kirchhoff’s radiation law indicates that a good absorber is also a good emitter. For example, a perfect blackbody radiates as well as absorbs all the radiations that fall on it. So naturally, a good reflector is also a poor absorber.

A black pot is a good absorber than the silvered pot and so it can absorb all the radiant heat incident on it faster. It can absorb radiation of all wavelengths for all the angles of incidence. There is a very small amount of reflection from a black body. Hence, it cools faster than any other non-black substance.

Conclusion:

Hence, the black pot will cool faster.