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Homework Help: Capacitors and inductors

  1. Sep 16, 2013 #1
    1. The problem statement, all variables and given/known data
    an electromagnet is operated at 50A. assuming an inductance of 100H for the magnet's coil, what voltage will be developed when the switch is opened? when it is closed? assume that the switch requires 1 millisecond to operate.

    2. Relevant equations
    I(t) = Vb/(R(1-e^(-tR/L)))

    3. The attempt at a solution
    with the given formula above I am not quit sure how to proceed if I am not given resistance. any insight on how I should proceed with this problem would be great!
  2. jcsd
  3. Sep 16, 2013 #2
    You could use Faraday's law of induction. It gives you the emf developed by a change in the magnetic flux.
  4. Sep 16, 2013 #3


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    Staff: Mentor

    Is there a circuit diagram to accompany this problem? Maybe that would give us a hint as to the where the resistance is supposed to be, or what might be in place to limit voltages, or what the implications are for a switch that "requires 1 millisecond to operate".
  5. Sep 16, 2013 #4
    no diagram but I figured it out.

    di/dt = 50A/10^-7
    V = L(di/dt)
    V= 5MV
  6. Sep 16, 2013 #5
    thank you everyone!
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