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Homework Help: Magnetic field of a coaxial cable

  1. Mar 3, 2005 #1
    The figure below is a cross-sectional view of a coaxial cable. The center conductor is surrounded by a rubber layer, which is surrounded by an outer conductor, which is surrounded by another rubber layer. In a particular application, the current in the inner conductor is 1.86 A out of the page, and the current in the outer conductor is 2.13 A into the page.

    FIGURE: http://east.ilrn.com/graphing/bca/user/appletImage?dbid=802444537 [Broken]

    (a) Determine the magnitude of the magnetic field at point a.
    (b) Determine the magnitude of the magnetic field at point b.

    I got part a, which is (mu*I1)/(2*pi*.002). I can't seem to get the right answer for part b. I tried (mu*I2)/(2*pi*.006), where I2 equals the current of the outer conductor. Also, I tried (mu*I3)/(2*pi*.002). All these still give me the wrong answer. What am I doing wrong?

    Please help me...Any help would be greatly appreciated! :)
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Mar 3, 2005 #2


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    For b) you need to take a circular Amperian loop of radius 6mm, and the enclosed current is I2 - I1. So if you apply Ampere's Law, the answer is mu*(I2 - I1)/(2*pi*0.006).
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