Module 5 : MODERN PHYSICS
Lecture 25 : Compton Effect
Compton Effect
Photoelectric effect provides evidence that energy is quantized. In order to establish the particle nature of radiation, it is necessary that photons must carry momentum. In 1922, Arthur Compton studied the scattering of x-rays of known frequency from graphite and looked at the recoil electrons and the scattered x-rays.
According to wave theory, when an electromagnetic wave of frequency $ \nu_0$ is incident on an atom, it would cause electrons to oscillate. The electrons would absorb energy from the wave and re-radiate electromagnetic wave of a frequency $ \nu_s < \nu_0$. The frequency of scattered radiation would depend on the amount of energy absorbed from the wave, i.e. on the intensity of incident radiation and the duration of the exposure of electrons to the radiation and not on the frequency of the incident radiation.
  Compton found that the wavelength of the scattered radiation does not depend on the intensity of incident radiation but it depends on the angle of scattering and the wavelength of the incident beam. The wavelength of the radiation scattered at an angle $ \theta$ is given by
 
$\displaystyle \lambda_s = \lambda_0 + \frac{h}{m_0c}(1-\cos\theta)$
  .where $ m_0$ is the rest mass of the electron. The constant $ h/m_0c$ is known as the Compton wavelength of the electron and it has a value 0.0024 nm.
   
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