Explain Einstein's theory of photoelectric effect.

Photoelectric effect: When certain metals are exposed to a beam of light, the electrons are ejected from the metal. This phenomenon is called the photoelectric effect. The electrons ejected are called photoelectrons.

The results of this experiment were:

1. The electrons are ejected from the metal surface as soon as the beam of light strikes the surface, i.e., there is no time lag between the striking of the light beam and the ejection of electrons from the metal surface.
2. The number of electrons ejected is proportional to the intensity or brightness of the light.
3. For each metal; there is a minimum frequency, {tex}\nu_o{/tex} below which photoelectric effect is not observed.
4. K.E. of electrons {tex}\propto{/tex} frequency of light.

Equipment for studying the photoelectric effect. Light of a particular frequency strikes a clean metal surface inside a vacuum chamber. Electrons are ejected from the metal and are counted by a detector that measures their kinetic energy:

Explanation of photoelectric effect on the basis of quantum theory: When a photon of sufficient energy strikes an electron in the atom of the metal, it transfers its energy to the electron and the electron is ejected without delay. Greater the energy of the photon, greater will be the kinetic energy of the ejected electron.