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Photoelectric effect


 
Figure :
Equipment for studying the photoelectric effect .light strike a clean metal surface inside a vacuum chamber. Electrons are ejected from the metal and are counted by a detector that measure their kinetic energy
H.Hertz in 1887 performed an experiment in which-  electrons were ejected when metal like K, Rb and Cs were exposed to a beam of light .This phenomena is called Photoelectric effect.

Following results are obtained in this experiment.
(i) The electrons are ejected from the metal as soon as light strike on the metal surface .
(ii) The number of electron ejected is proportional to the intensity of light.
(iii) For each metal, there is characteristic minimum frequency   (also known as threshold frequency ) below which photoelectric effect do not observe and electrons are eject with certain kinetic energy.

All the above result could not explain by classical wave theory of light. According to which number of electron ejected and kinetic energy should depend upon intensity of light. But it has been observed that number of electrons ejected depend upon intensity of light but its kinetic energy does not. Kinetic energy of these electrons depends upon frequency of light.

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