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Compton Effect

  1. Apr 23, 2005 #1
    If the maxmimum energy imparted to an electron in Compton scattering is 45 keV what is the wavelength of the incident photon?

    So a compton scattering happens and the energy is 45 keV and I need to find the wavelength of the photon incident to this electron. I think I need to use

    Lambda = h/mc (1-Cos), but I am not given an angle.
     
  2. jcsd
  3. Apr 23, 2005 #2

    OlderDan

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    Maximum energy corresponds to (minimum/maximum, you decide) wavelength change? Which angle gives the (minimum/maximum) wavelength change?

    Your equation is missing something. It is not quite correct in two places. For one, the angle for the cos is missing. What else?
     
    Last edited: Apr 23, 2005
  4. Apr 23, 2005 #3

    jtbell

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    Imagine you're playing billiards. You shoot the cue ball (photon) against the eight-ball (electron), with a certain amount of energy. What direction does the cue ball go after the collision, when it transfers the maximum amount of energy to the eight-ball?
     
  5. Apr 23, 2005 #4
    The cue ball will go in reverse fro mthe way it came?
     
  6. Apr 24, 2005 #5

    OlderDan

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    Yes, although in the case of a cue ball that has no backspin there is no rebound because the masses of the balls are the same. But if you had a cue ball of lesser mass, it would bounce back. And if you had a cue ball of greater mass, it would keep going forward in a stratight line when the maximum energy is transferred.
     
  7. Apr 24, 2005 #6
    So there is the collision and there is no rebound, but the 8 ball (electron) does go forward and now has the energy from the cue ball (photon)
     
  8. Apr 24, 2005 #7
    correct! they have the same masses, so the cue ball transfers all of its energy to the eightball making it move forward and the cue ball come to a halt.
     
  9. Apr 24, 2005 #8

    jtbell

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    Bleah, I forgot about the mass considerations... with equal masses and if topspin doesn't come into play, the cue ball simply comes to a dead stop in a head-on collision with a stationary eight-ball.

    I should have specified something like a ping-pong ball hitting the eight-ball. After all, the photon is massless.
     
  10. Apr 24, 2005 #9

    OlderDan

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    There will be a rebound in the Compton effect problem, and the angle that will give the electron greatest energy is when the rebound photon is straight back.
     
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