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Homework Help: Why light exerts pressure on a metal surface

  1. Dec 1, 2012 #1
    1. The problem statement, all variables and given/known data

    By considering the E and B fields of an incident monochromatic plane wave on a metal surface, as well as the current density of mobile electrons, J and the resulting EM force F felt by them, show that there is a force on the metal due to the magnetic force on the mobile electrons.

    2. Relevant equations

    [tex] \vec F = q( \vec E + \vec v \times \vec B ) [/tex]

    [tex] \vec E = E_0 e^{ky-wt} \hat k [/tex]

    [tex] \vec B = \frac{E_0}{c} e^{ky-wt} \hat i [/tex]

    3. The attempt at a solution

    Let the surface be the zy plane. Then at the surface we have

    [tex] \vec E = E_0 e^{-wt} \hat k [/tex]
    [tex] \vec B = \frac{E_0}{c} e^{-wt} \hat i [/tex]

    Consider a mobile electron on the surface. The E field will cause the electron to move in the -z direction. Then since the electron is now moving, the B field will exert a force in the
    [tex] - \hat k \times \hat i = \hat j [/tex]
    direction. Applying this to all mobile electrons we get a net force in the y direction on the surface.

    I just wanted to see if my logic here is correct.. Am I missing any important details?

    Any reply would be great.. thanks!

  2. jcsd
  3. Dec 1, 2012 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Looks right to me!
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