Compton Effect:
Photoelectric effect proved quantum theory of light at basic level.
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It
confirmed that light consist of individual photon that carry energy, depends
upon frequency of oscillation of light.
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Another
experiment that proved quantum theory of light was Compton effect
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In
Compton effect, Compton makes electromagnetic waves with shorter wavelength (x
rays) to fall at stationary electron,
·
he
examined collision between the electromagnetic waves and electron,
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he
found that reflected electromagnetic wave has greater wavelength than the wave
incident on electron on collision.
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“Wavelength of the scattered X rays was larger than incident X rays
in collision of X rays and a stationary electron, this effect is known as
Compton effect”
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Using
conservation of energy and momentum, he was able to derive the following
equation,
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Compton
shift =shift in wavelength
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This
is known as Compton shift
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Now
question arises how Compton Effect proves quantum theory of light?
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According
to wave theory there is no change take place in wavelength in any collision.
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The
incident electromagnetic wave cause electron to oscillate with same frequency
as that of incident waves when the electron reemitted the waves its must be of
same frequency as that of incident waves so there is no shift in frequency
which implies there is no shift in wavelength according to wave theory
·
But
this is not happen in actual experiment conducted by Compton, in Compton experiment
there is a shift in Wavelength.
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It
proves that wave theory is not applicable here, from quantum theory of light ,lets
examined Compton experiment through quantum theory of light and found that it is applicable or not
·
Lets
photon collides with that stationary electron and in this collision some of
energy within photon goes into the electron, (similarly the case of particles
collision in which transfer of energy take place).
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Now,
electron gain kinetic energy and begin to move with same velocity and scattered
photon has less energy than before.
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Energy
depends on frequency, less energy means less frequency and smaller frequency
means greater wavelength as frequency is inversely proportional to wavelength.
·
So
that scattered waves has larger wavelength and therefore quantum theory of light
is successfully describe Compton experiment related to Compton effect and its contrary is also true.