Question

Describe an experiment to show that a black (or dull) surface is better absorber of heat radiations than polished one.

Answer 1

Keep any black and shiny object in Sunlight or close to a heat-emitting object that will help in understanding the experiment clearly.

Complete step by step answer:
Consider a polished tea pot and over-used dull black tea pot. Now put water in both the tea pots and keep them under the Sun. After every five minutes, take a reading of the temperature of the water in each teapot, using a thermometer. Record the reading. After an hour, analyze the readings taken. You will observe from that the temperature of the water in the dull tea pot increases more rapidly than that of the polished one.
Thus, it can be concluded that black (or dull surface is better absorber of heat). The temperature of the water in a polished tea pot increases slowly, because the outer polish surface reflects most of the radiation incident on it.

Additional Information:
Good absorbers are good emitters also. The black tea-pot when removed from sunlight cools down more quickly than the polished teapot, as it rapidly radiates heat.
As black or dull surface is better absorber of heat radiations than polished one, the bottom of cooking utensils are kept rough so that they absorb more heat from the burner and cook the food rapidly.

Note:
A perfectly black body is one that absorbs all the radiation incident on it. A black body therefore neither transmits or reflects any radiation. A perfectly black body is also obviously an ideal conception.