Q. Assertion : A hollow metallic closed container with small opening maintained at a high temperature can act as a source of black body radiation.
Reason : All metals act as black body radiator.

 2145  248 AIIMSAIIMS 1996Thermal Properties of Matter Report Error

Solution:

All metals have got different physical characteristics, due to which they will be having different emissive and abosorptive powers, so all metals cannot act as black bodies. But a hollow metallic closed container can act as a blackbody. If a small hole is made on the surface of the hollow container whose inner surface is painted black and the shape is as shown in the figure, then any radiation that enters the hole has a good chance of being absorbed after multiple reflections taking place on the inner surface of the container. And thus it can act as a blackbody.
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