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Homework Help: Compton Effect Derivation

  1. May 14, 2007 #1
    oK SO.... I have been given the task of deriving the Compton effect equ. ( [tex]\lambda\prime-\lambda=\frac{h}{m_ec}(1-cos\theta)[/tex])
    exactly from the 3 following:
    1) [tex]\frac{h}{\lambda}=\frac{h}{\lambda\prime}cos\theta +\gamma m u cos\phi[/tex]

    2) [tex]0=\frac{h}{\lambda\prime}sin\theta-\gamma mu sin\phi[/tex]

    3) [tex]\frac{hc}{\lambda}=\frac{hc}{\lambda\prime}+(\gamma-1)mc^2[/tex]

    I found the link
    however I am having a hard time going from my equations to momentum and energy conservation
    any ideas where to go ... I have been at it for 4+hrs and its driving me nuts
  2. jcsd
  3. May 14, 2007 #2


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    To get rid of term of [tex]\phi[/tex], try

    [tex]\frac{h}{\lambda}\,-\,\frac{h}{\lambda'}cos\theta\,=\,\gamma m u cos\phi[/tex]

    [tex]\frac{h}{\lambda'}sin\theta\,=\,\gamma mu sin\phi[/tex]

    Square both equations and add.

    Now, IIRC, [itex]\beta[/itex] = u/c and [itex]\gamma[/itex] = [tex]\frac{1}{\sqrt{1-\beta^2}}[/tex]
  4. May 14, 2007 #3
    1 and 2 are from momentum conservation and 3 from energy conservation.

    First you need to eliminate Phi from the two first equations using the indentity cos^2(phi)+sin^2(phi)=1. Yes, you need to square up these equations after moving all other terms to one side except one with Phi.
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