Question

How can the radiating power of a surface be increased?

Answer 1

From the concept of Kirchhoff’s law of radiation, we can say that the ratio of emissivity and absorptivity have identical values for all objects at a specific temperature and corresponding to black body’s emissivity at that temperature.

Complete step by step answer:

The emissivity of the given surface is the ratio of total radiation emitted by it and the total radiation emitted by a black body. In other words, we can say that using emissivity we can tell about the efficiency of the given surface to emit thermal radiations. Whereas, by the value of absorptivity of the given surface, we can tell about the thermal radiations absorbed by the surface.
Leslie, a scientist, experimented using a cube, commonly known as Leslie cube and found that the radiating power of a surface depends on its nature and its absolute temperature. He also concluded that the rough and dark surface has high emissivity and absorptivity.
Therefore, we can say that the radiating power of a surface can be increased by converting it into a rough and dark surface.

Note: In Leslie experiment, one black, one white, one shiny and one matt surface enclosed inside the cube are heated to a temperature of $100^\circ {\rm{ C}}$ with the help of boiling water. Moll thermopile is an instrument which was used to measure the intensity of radiation in this experiment. The different values of radiation intensity are measured at different time intervals till the temperature of the cube reaches atmospheric temperature.