Question

Consider two separate objects of unequal temperature. What would you do with them and what would have to happen thereafter to enable them to reach the same common temperature? Use this idea to explain why the electromagnetic radiation enclosed in a cavity has a temperature that is the same as that of the cavity walls.

Short answer

The temperature of electromagnetic radiation enclosed in a cavity has the same temperature as the cavity walls due to thermal equilibrium.

Step-by-step solution

Given data

The two objects at unequal temperatures are enabled to reach the same temperature.

Concept used

Thermal equilibrium: It is a state of equilibrium in which the temperature of both the objects become the same, and there is no further transfer of heat.

Electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field propagating through space, carrying electromagnetic radiant energy.

Heat transfer

To make the temperatures of both the objects the same, one has to bring them in contact. Once they are in contact, the heat starts to flow from a higher temperature object to a lower temperature object. The process of heat transfer continues until they reach a state of thermal equilibrium.

Electromagnetic radiation

The above idea holds true for electromagnetic radiation enclosed in a cavity. The electromagnetic radiation radiates heat which is absorbed by the cavity. This radiation of heat occurs until thermal equilibrium is achieved. At thermal equilibrium, both the radiation inside the cavity and the cavity walls have the same temperature.