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# What is the Compton Effect?

## Compton Effect

Compton in 1923 performed an experiment and discovered the most important confirmation about the particle aspect of radiation.

By scattering X-rays off free electrons, he found that the wavelength of the scattered radiation is larger than the wavelength of the incident radiation. As a result we can say that this explanation can be made by assuming that the X-ray photons behave like particles.

According to classical physics, the incident and scattered radiation should have the same wavelength. We know that the energy of the X-ray radiation is too high so it is not absorbed by a free electron. Therefore the incident X-ray would then provide an oscillatory electric field due to which the electron executes oscillatory motion. Hence it radiate light with the same wavelength but with an intensity I that depends on the intensity of the incident radiation I0. But these two predictions of classical physics are not in accordance with the experiment.

By experiment Compton reveals that the wavelength of the scattered X-radiation increases by an amount , called the wavelength shift and that  depends not on the intensity of the incident radiation, but only on the scattering angle.

After treating the incident radiation as a stream of particles (photons) colliding elastically with individual electrons, Compton is able to explain his experimental results successfully.

## Compton’s Experimental Observation:

• The wavelength shift of the X-rays is independent of the frequency (or wavelength) of the incident photons. It depends only on the scattering angle.
• The Compton Effect confirms that photons are particles in nature. They collide with electrons like material particles.

## Mathematically Determination of Compton’s Wavelength Shift

Mathematical derivation leads to the value of wavelength shift

Where λC = h/mec = 2. 426 x 10-12 m is the Compton wavelength of the electron. The above equation relates the initial and final wavelengths to the scattering angle.

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