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Question : 14
Total: 26
Using photon picture of light, show how Einstein's photoelectric equation can be established. Write two features of photoelectric effect which cannot be explained by wave theory.
Solution:
Photon picture plus Einstein's photoelectric equation
Two features
In the photon picture, energy of the light is assumed to be in the form of photons, each carrying an energy hv.
Einstein assumed that photoelectric emission occurs because of a single collision of a photon with a free electron.
The energy of the photon is used to
(i) Free the electrons from the metal.
[For this, a minimum energy, called the work function( = W )
And
(ii) Provide kinetic energy to the emitted electrons.
Hence
( K.E. ) max = h v − W
(
m v max 2 = h v − W )
This is Einstein's photoelectric equation
Two features (which cannot be explained by wave theory):
(i) 'Instantaneous' emission of photoelectrons
(ii) Existence of a threshold frequency
(iii) 'Maximum kinetic energy' of the emitted photoelectrons, is independent of the intensity of incident light
Two features
In the photon picture, energy of the light is assumed to be in the form of photons, each carrying an energy hv.
Einstein assumed that photoelectric emission occurs because of a single collision of a photon with a free electron.
The energy of the photon is used to
(i) Free the electrons from the metal.
[For this, a minimum energy, called the work function
And
(ii) Provide kinetic energy to the emitted electrons.
Hence
This is Einstein's photoelectric equation
Two features (which cannot be explained by wave theory):
(i) 'Instantaneous' emission of photoelectrons
(ii) Existence of a threshold frequency
(iii) 'Maximum kinetic energy' of the emitted photoelectrons, is independent of the intensity of incident light
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