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Faraday's Law question

  1. Nov 26, 2008 #1
    1. The problem statement, all variables and given/known data
    A circular loop of radius r = 12cm is in a uniform magnetic field B=.5T w/ its plane normal to the direction of the field. If the magnitude of B then decreases at a constant rate of -.01T/s, at rate should r increase so the induced emf in the loop is zero?

    2. Relevant equations
    Faraday's Law

    3. The attempt at a solution
    The question gives the initial emf in the loop = .01V and you can solve for the initial flux =.0023Wb. From here I don't know what to do.
  2. jcsd
  3. Nov 26, 2008 #2


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    Gold Member

    If both the radius and the field are changing, what is the formula for the induced emf?


    You should have two terms in your equation, one involving the rate of change of B and one involving the change in r. You then want to pick a value for the rate of change of r such that both terms cancel.
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