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Homework Help: Magnetic flux and emf through a rotating ring

  1. Apr 26, 2009 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 26, 2009 #2
    Sorry I don't quite know how that happened!
    Any way the question is
    "A metal ring of radius R rotates with constant angular velocity about a diameter. Perpendicular to the rotation axis is a constant magnetic field B. Calculate as functions of time
    a) magnetic flux through ring
    b) emf induced

    I know magnetic flux = BAcoswt
    so emf = -magnetic flux/dt = ABwsinwt
  4. Apr 26, 2009 #3
    arent you missing a minus sign in your final answer?
  5. Apr 26, 2009 #4
    emf = -dphi/dt = -d/dt(BAcoswt) = -(-BAwsinwt) = ABwsinwt
    i think
    I am a bit confused by the fact that they say "about a diameter" how does this change things?
  6. Apr 26, 2009 #5
    ok. yeah my bad with the minus. the diameter bit just tells you the way its rotating its not rotating about the surface normal but rather like a dynamo would.
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