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Homework Help: Find current given magnetic field

  1. Oct 29, 2016 #1
    1. The problem statement, all variables and given/known data
    Suppose a straight 1.90 mm diameter copper wire could just "float" horizontally in air because of the force due to the Earth's magnetic field [PLAIN]http://www.webassign.net/images/boldB.gif, [Broken] which is horizontal, perpendicular to the wire, and of magnitude 4 ✕ 10-5 T. What current would the wire carry?

    2. Relevant equations
    F = ILB

    3. The attempt at a solution
    It seems like a simple question but the phrasing is a bit confusing and I'm having trouble visualizing it. So the F vector is pointing up in the k-direction because it's pushing the wire up, right? The B vector is horizontal so let's say in the i-direction, but how is it perpendicular to the wire if the wire is also floating horizontally?

    So far, all I could do is rearrange the force equation to
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Oct 29, 2016 #2
    Also, I believe F should be equal to Fg since the wire is floating in the air.

    Ah, also I think B should be going into the page?
    Last edited: Oct 29, 2016
  4. Oct 31, 2016 #3
    So update:

    I = 9.8N/ L*(4x10^-5 T)

    How am I supposed to get L?
  5. Nov 3, 2016 #4

    rude man

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    Where did you get 9.8N from? You're implying (whether you know it or not) that your wire has mass of 1 kg. So what's the length of 1 kg of Cu wire with diameter 1.9mm?[/QUOTE]
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