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Homework Help: Rate of Magnetic Field Change and current

  1. Apr 10, 2010 #1
    1. The problem statement, all variables and given/known data

    A single conducting loop of wire has an area of 7.2×10−2m2 and a resistance of 120 ohms. Perpendicular to the plane of the loop is a magnetic field of strength 0.50 T.

    At what rate must this field change if the induced current in the loop is to be 0.39A?

    2. Relevant equations

    Rate of change = emf/-N

    3. The attempt at a solution

    Rate of change = emf/-N

    It's a single loop, so N should be 1
    Rate of change - emf/-1


    Rate of change = -IR
    Rate of change = -(.39A)*120ohms=-46.8

    This isn't right though.

    Thanks for the help :)
    Last edited: Apr 10, 2010
  2. jcsd
  3. Apr 11, 2010 #2
    anyone? :)
  4. Apr 11, 2010 #3


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    Science Advisor
    Homework Helper
    Gold Member

    The correct equation is

    emf = - dΦ/dt

    where Φ is the magnetic flux through the loop which you need to calculate first.
  5. Apr 11, 2010 #4
    Arggh, I've been reading it as magnetic field, not flux. Thanks!
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