Moder Physics

Emission of Electrons:

At room temperature the free electrons moves randomly within the conductor, but they don't leave the surface of the conductor due to attraction of positive charges. Some external energy is required to emit electrons from a metal surface. Minimum energy is required to emit the electrons which are just on the surface of the conductor. This minimum energy is called the work function (W). The work function is the property of the metallic surface.

The energy required to liberate an electron from metal surface may arise from various source such that as heat, light, electric field etc. Depending on the nature of source of energy, the following methods are possible: