Question

What is photoelectric effect? State the result of photoelectric effect experiment that could not be explained on the basic of laws of classical physics. Explain this effect on the basic of quantum theory of electromagneic radiation.

Answer 1

Photoelectric effect: When certain metals are exposed to a beam of light, the electrons are ejected from the metal. This phenomenon is called photoelectric effect. The electrons ejected are called photoelectrons.
The results of this experiment were:
1. The electrons are ejected from the metal surface only as the beam of light strikes the surface.
2. The number of electrons $$\propto$$ intensity of radiation.
3. For each metal; there is a minimum frequency, $$v_{0}$$ below which photoelectric effect is not observed.
4. $$K.E.$$ of electrons $$\alpha$$ frequency of light.
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 electron and the electron is ejected without delay. Greater the energy of the photon, greater will be the kinetic energy of the ejected electron.