Define thermal radiation and radiant energy and explain Provost theory

Explanation

Thermal radiation : ..All substances emit electromagnetic waves of certain definite frequencies depending on their temperature. This radiation is called thermal radiation...
Thermal radiation are electromagnetic radiation but all electromagnetic radiation are not necessarily thermal radiation.
Radiant energy : ..The energy associated with the electromagnetic waves in thermal radiation is called the radiant energy...
Provost.s theory : According to Provost.s theory, every substance emits radiation at any temperature.
The rate of emission of thermal radiation increases with the increase in temperature.
At the same time the body absorbs radiation emitted by other substances.
If the rate of emission of body is more/less than the rate of absorption of heat radiation, the temperature of the body decreases/increases.
When its temperature becomes equal to that of surrounding, the rate of emission and rate of absorption of thermal radiation become equal.
The amount of different frequencies present in thermal radiation depend on the temperature of the body and the type of its material.