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Question
What is photoelectric effect? State the result of photoelectric effect experiment that could not be explained on the basis of laws of classical physics. Explain this effect on the basis of quantum theory of electromagnetic radiations.
Solution
When the beam of light gets exposed to the metal surface then the electrons get emitted from the metal. This effect is said to be photoelectric effect and the emitted electrons are said to be photoelectrons.
The result of photoelectric experiment are as follows:-
(i) There is no time gap between the striking of a light beam and the ejection of electrons from the metal surface i.e. electrons emit as soon as a beam of light strikes the metal surface.
(ii) The number of electrons ejected is directly proportional to the intensity of light.
(iii) For every metal there is minimum emitting frequency which is said to be threshold frequency, `ν_o`. The kinetic energies of these electrons is directly proportional to the frequency of the light used.
As per the quantum theory of electromagnetic radiation when a photon with energy greater than the threshold energy of the metal strikes the metal then the electrons get emitted from the metal without any delay and its kinetic energy depends upon the frequency of the light.
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