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Homework Help: Magnetic flux in a coil, find current

  1. May 6, 2008 #1
    1. The problem statement, all variables and given/known data

    1.) Problem (exam question that I got wrong and want to figure it out)
    A circluar coil of radius a=.35m rotates at a frequency of 120 hz in a constant magnetic filed of B=.8T. The axis of rotation is perpendicular to the field the coil has N =340 turns it has a resistance R=50 ohms
    a.) what is flux thru coil t=0 if the normal vector of the coil is at an angle of 45 degrees to magnetic filed?
    b.) suppose the coil starts rotating, what is its flux as a function of time?
    c.) what current runs through the coil? peak current? RMS current?
    d.)if coil connected to capacitor, what is current thru cap.(ignore the resistance)? peak current? what energy is stored in the capa.? where is it stored?
    e.) answer the same for a resistor.

    2. Relevant equations
    i = e/R
    flux = NBAcos(angle)
    e = - delta flux/ delta t

    3. The attempt at a solution

    a) flux = NBAcos(angle) = 340 x .8 x pi x (.35) ^2 cos(45) = 74.01
    b) e = - delta flux / delta t, so - 74.01 x d/dt where do I get time, is it t = 1/f f = 120 hz?
  2. jcsd
  3. May 6, 2008 #2
    Could you maybe draw a picture? I don't understand how this is set up, which direction the field is pointing, which direction the coil is aligned in, and which way it is spinning.
  4. May 6, 2008 #3
    I wish I could but that is all the information I was given. I been banging my head on the desk for hrs trying to understand.
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