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Homework Help: Inductance & magnetic flux problem - please help

  1. Nov 15, 2008 #1
    Inductance & magnetic flux problem -- please help

    1. The problem statement, all variables and given/known data
    The magnetic field of a place on Earth has strength 55 microTesla and is tilted 60 degrees below horizontal. A 200 turn coil with diameter 4cm and resistance 2 ohms is connected to a 1 microFarad capacitor. The coil is held in a horizontal plane and the capacitor is discharged. Then quickly the coil is rotated 180 degrees. Afterwards, what is the voltage on the capacitor?

    2. Relevant equations

    3. The attempt at a solution
    I have the flux through the coil initially:

    = pi* (.02)^2 * (5.5e-5) * cos (30) * 200 = 1.2 e -5 Wb

    But I really don't understand what happens when the capacitor discharges. Also, how does just flipping the loop over will change the flux to induce a current? It seems to me that the angle doesn't change or anything. Please help.
  2. jcsd
  3. Nov 15, 2008 #2
    Re: Inductance & magnetic flux problem -- please help

    Any ideas? This is really bugging me that I don't understand this very well.
  4. Nov 16, 2008 #3
    Re: Inductance & magnetic flux problem -- please help

    hmmm... ok
    So I guessed that the flux would be the same when flipped only with the opposite sign:

    (1.2e-5)--(1.2e-5) = change in flux = 2.4 e-5 Wb

    (2.4e-5)/dt = EMF

    (2.4e-5)/(2ohm)dt = dq/dt

    dq= 1.2 e-5 C = (1e-6F)Vc
    Vc = 12 V

    I do have another question though. The capacitor would discharge again after being rotated, right?
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