Consider a small body placed inside a large enclosure whose interior walls are at a…
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
Consider a small body placed inside a large enclosure whose interior walls are at a uniform temperature T. The enclosure has a tiny hole through which radiation can escape to the outside.
(i) Assuming the body and the hole each come to thermal equilibrium with the enclosure, set up the equality of radiant energy absorbed and emitted by the body for radiation of a particular wavelength λ.
(ii) From the condition in part (i), show that the emissivity ελ of the body at wavelength λ must equal its absorptive power aλ at the same wavelength.
(iii) Using the result of part (ii), explain why substances that absorb strongly at a given wavelength also emit strongly at that wavelength, citing two practical examples from everyday life.