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Homework Help: Magnetic Field from Sheets of Current

  1. Jul 15, 2009 #1
    1. The problem statement, all variables and given/known data

    Two infinite sheets of current flow parallel to the y-z plane. The left-hand sheet, which intersects the x-axis at x = 0, consists of an infinite array of wires parallel to the z-axis with a density n = 990 wires/m and a current per wire of IL = 0.19 A in the +z direction. The right-hand sheet, which intersects the x-axis at x = a = 10 cm, is identical to the left-hand sheet, except that it has a current per wire of IR = 0.19 A in the -z direction.
    https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2112/summer/homework/Ch-26-B-Force-and-Fields/B-field-from-sheets/0805.gif [Broken]
    Calculate the y-components of the net magnetic field at x = 5 cm

    2. Relevant equations

    Ampere's Law: [tex]\mu[/tex]o*I/(2*pi*r)

    3. The attempt at a solution

    I thought I would only have to use Ampere's Law for each sheet, so my equation looked like this:
    B = [tex]\mu[/tex]o(.19)/(2*pi*.05)
    I multiplied this answer by two, since they have the same current and are the same distance away, but the solution was incorrect.

    Any suggestions?
    My only guess is that I'm treating it like a line rather than a sheet, but even if you take dB, it turns out to be the same equation.

    Thanks in advance!
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jul 16, 2009 #2
    B = 0
    Look for symetry. I'll explain more later. Must sleep.
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