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2 Questions about EM wave propagation

  1. Oct 23, 2011 #1
    I was just reading about EM wave propagation and had two questions I would appreciate an answer to.
    1-I read how the electric and magnetic fields of an EM wave oscillate sinusoidally and perpendicular to each other and the direction the wave is traveling. Is there any significance or special properties of an EM wave when the E and B fields are at zero or both on the axis in the direction of propagation?

    2-As I understand it, EM waves can travel indefinitely in a vacuum, but not in matter. What is it that causes waves in matter to (for lack of a better word) stop or wear out? Is the energy in a wave converted to another form when it hits the atoms of the matter it is traveling through?

    If it is easier, you can post a link that explains the answers. Thanks
  2. jcsd
  3. Oct 23, 2011 #2


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    I'll have a go at 1. It just means E = 0 or B = 0 (never both) periodically at any point in space. It is like noticing that as a water wave passes you there are times when the water level is normal (as if there was no wave).

    EM waves are attenuated in matter due to them exerting forces on charged particles, transferring energy to them. The wave makes the electrons move, perhaps even pulling some away from their atoms.
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