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How to determine where the B feild starts

  1. Dec 16, 2011 #1
    This is kind of a simple question but if an EM wave is propagating in the positive x direction and the E field starts in the positive z direction, how do you figure out if the B field starts in the - or + y direction?

  2. jcsd
  3. Dec 16, 2011 #2

    Simon Bridge

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    Have a look:

    in the article, v is in the +y dir, +E is in the +z dir, so B is in the +x direction.
    to get your situation, rotate the axis anti-clockwise about +z ... now v is in the +x direction and B starts out in the -y direction.

    The relationship depends on the cross product in the wave equation.
    (Scroll down the link for derivation.)

    note: the end-on animation shows the view looking down the direction of v.
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