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Light Behavior

  1. Jun 24, 2008 #1
    Do photons reflected off prisms exert directional force however small as they are reflected off the hypotenuse side of a right triangle shaped prism?
  2. jcsd
  3. Jun 25, 2008 #2


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    Staff: Mentor

    Light carries momentum, which is a vector quantity, that is, it has both magnitude and direction. Therefore, if a beam of light changes direction, something must recoil in order for the total momentum to be conserved. This is true in both the classical and quantum models of light.
  4. Jun 25, 2008 #3
    I fully agree with jtbell answers. I would like to point out that the original question suggests that photons can somehow bounce off a surface. Technically however, photons being massless cannot be put at rest, so must be absorbed and re-emitted. Maybe just nitpicking :smile:
  5. Jun 25, 2008 #4


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    Gold Member

    Wow, I never thought a reflection or an elastic scatter involved a state of rest. However, I can accept that absorption and re-emission is mathematically equivalent to a reflection or a scatter. Is this really the way it is treated in QM or QFT? Also, is the momentum of the reflection absorbed by a single atom, or by the entire prism or mirror, similar to the Mossbauer effect?

    Inquiring minds want to know. TIA.
    Jim Graber
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