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Homework Help: Help with electromagnetism problem

  1. Jul 27, 2008 #1
    1. The problem statement, all variables and given/known data

    An airplane with a wingspan W = 30 m is flying due north at v = 672 km/h. The Earth's field is 1.210-4 T, due north and inclined q = 42 below horizontal. What is the magnitude of the potential difference between the ends of the wings?

    2. Relevant equations

    Magnetic flux: φ = B · A · cosθ

    Induced potential difference (emf)
    due to a changing magnetic field: V = -N · ∆φ/∆t

    Motional emf: V = -B · L · v

    Could be any one of these. Also, the problem said to treat it like pulling a rectangular wire through a magnetic field, and find the area facing the field using the angle.

    3. The attempt at a solution

    It seems this is more of a riddle than a problem. How do I find the area facing the magnetic field? I'm only given the wingspan!
  2. jcsd
  3. Jul 27, 2008 #2


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    The wingspan gives you the length dimension of conducting rod right? So how can you get the width given the velocity of the plane?
  4. Jul 27, 2008 #3
    Well, the plane is traveling into the field, so I would think the wingspan is the width. So it's the length I don't have. And it's not a conducting rod. The hint said to do the problem as if it was a rectangle circuit, and anyway I don't think there would be any potential difference if it was just a rod.
  5. Jul 27, 2008 #4


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    Depending on your setup and how the conducting rod is moving with respect to the magnetic field, you can interpret the wingspan as either the width or length. The term conducting rod is just to relate the situation to a very similar one which you are familiar with.

    EDIT: By the way I can't access your picture. It's appears to be "forbidden access".
  6. Jul 27, 2008 #5
    Bah. It's from Apex (Not) Learning. I'll mirror it on Imageshack. Here you go.

    http://img401.imageshack.us/img401/892/ba9416055eb44e21a8ebb2cwy2.th.gif [Broken]

    Well whatever the wingspan is, I need another dimension, and Apex is being really anal about not giving me any hints. Would I just use like 1 meter or something?

    [gripe] And HOW is this related to the chapter? I don't remember seeing 'riddles' in the curriculum for electromagnetism! [/gripe]
    Last edited by a moderator: May 3, 2017
  7. Jul 28, 2008 #6


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    There is already another dimension. The plane is not stationary, it's moving at a constant speed. You need to find the rate at which the conducting wings pass through the magnetic field lines, which would then give rise to a potential difference.
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