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How will the force of Light change with absorbtion/reflection?

  1. Feb 8, 2013 #1
    I am confused about whether or not the force that light exerts on an object (let's say that the power it has is 1 Watt) changes whether is is absorbed or reflected.

    I know that W = Fv, but is there more to it than that?

    Thank you for the help!
  2. jcsd
  3. Feb 8, 2013 #2

    Simon Bridge

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    conservation of momentum.
  4. Feb 8, 2013 #3
    For black materials (assuming black is equivelent to absorbs all frequencies) the light is absorbed, which means, that if the light photon had momentum p, the change of momentum is also p. On the other side a white material would in fact not absorb the energy, but change the direction on the photons, which would imply a change in momentum of 2p. Now just remember, that F=dp/dt and you have your answer.
  5. Feb 8, 2013 #4


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    I think you are asking about nonlinear optics. For sufficiently high powered light, the index of refraction may change.
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