In a particular case of compton scattering, a photon collides with a free electron and scatters backwards. the wavelength after the collision is exactly double the wavelength before the collision. what is the wavelength of the incident photon?

hence initial wavelength is

Explanation:

shift in wavelength due to compton effect is given by

λ' = the wavelength after scattering

λ= initial wave length

h= planks constant

m_{e}= electron rest mass

c= speed of light

θ= scattering angle = 180°

compton wavelength is

 ( put cos 180°=-1)

also given λ'=2λ

putting values and solving we get

hence initial wavelength is