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Homework Help: Magnetic field by moving plate capacitor ?

  1. Oct 18, 2015 #1
    1. The problem statement, all variables and given/known data

    A large parallel plate capacitor with uniform surface charge σ on
    upper plate and −σ on lower is moving with a constant speed v.

    Q1]Find the magnetic field between the plates and also above and below them.

    2. Relevant equations

    3. The attempt at a solution

    I know that above the top capacitor, direction of B is out of the page and into the page below the top capatitor.

    and as for the bottom capacitor, above : into the page , below : out of the page.

    so, between the plate , same amount of B are added into the page.

    but i can't understand why above and below both plates the fields cancel
  2. jcsd
  3. Oct 18, 2015 #2


    User Avatar
    2017 Award

    Staff: Mentor

    They have the same magnitude (for the approximation of infinite sheets) but opposite direction.
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