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Homework Help: Compton Scattering of a photon

  1. Sep 25, 2014 #1
    A photon with wavelength lambda = 0.1050 nm is incident on an electron that is initially at rest. If the photon scatters at an angle of 60.0 degrees from its original direction, what are the magnitude and direction of the linear momentum of the electron just after the collision with the photon?

    Hey guys, was wondering if someone could help me out with this, I understand I have to use conservation of momentum, so I have for x direction (I'll be using y for lambda here): h/y=h/y'+Pecos(theta)

    so Pe =cos theta( h/y-h/y' ) but this seems to be wrong, I'm not sure why, I just need to understand why this isn't right, thanks.
  2. jcsd
  3. Sep 25, 2014 #2


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    ##\small h/\lambda## is correct for the x-component of momentum of the incident photon. But ##\small h/\lambda '## is not correct for the x-component of momentum of the photon after the scattering. It goes off at a ##\small 60^o## angle.
  4. Sep 25, 2014 #3
    Oh thank you very much I see where I made my mistake :)
  5. Sep 26, 2014 #4


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    Also, note that the photon scattering at 60 degrees does not mean the electron does. You need to use conservation in both directions to find the linear momentum components of the electron. After that you have to find some way of also extracting the wavelength of the photon after scattering.

    Also, I really suggest that you use the homework template and fill in the relevant equations. This problem can be tackled with different levels of sophistication depending on how much relativity you know.
  6. Sep 26, 2014 #5
    Thanks, but I figured it out :)!
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