Question

Shining bodies are _______ absorbers of radiant heat.

Answer 1

Hint We know the various properties of thermal radiation. We can use the property of thermal radiation where the reflection of radiant heat takes place according to the law of reflection to answer this question.

Complete step by step answer
We know when a surface is polished, and it becomes shining, a major part of heat is being reflected.
Hence, shining bodies are a bad absorber of radiant heat. We can experimentally prove it by checking the emissive power of different surfaces. Let us take a metal box which is filled with water and coat its four surfaces with different materials with two surfaces having a coating of lamp black and a polished surface. Now, to observe the emissive power connect a thermopile with a galvanometer and keep in front of the surface at the same distance. We will observe the deflection shown in the galvanometer. You will see that the deflection due to black surface will be maximum while the shining surface is the least.

Additional information
Thermal Radiation is the process of transfer of heat from one body to another body without the help of any medium. Example- the sun rays reaching earth is an example of thermal radiation. Thermal radiation can also travel through vacuum and they travel in straight line with the speed of light.

Note:
It should be noted that a black body need not appear in black color, it is only the body which absorbs maximum incident heat. From the above experiment, we can also conclude that a surface which is a good absorber is also a good emitter and the one which is a bad absorber is also shown to be a bad emitter.