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Homework Help: Faraday's law and current

  1. Mar 29, 2006 #1
    I was wondering about the following problem:

    You are looking down on a single coil in a constant magnetic field B = 0.9 T which points directly into of the screen. The dimensions of the coil go from a = 6 cm and b = 15 cm, to a* = 20 cm and b* = 19 cm in t=0.028 seconds. If the coil has resistance that remains constant at 1.7 ohms, what would be the magnitude of the induced current in amperes?

    Now, I have the answer, and I was told how to get it. I used the formula I = (delta A*B)/(delta t*R)

    What I was wondering was if someone could tell me what rule or law this formula came from? I can't figure out how to derive it from any of the formulas given in this chapter. Thanks a lot.
  2. jcsd
  3. Mar 29, 2006 #2


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    This is an application of Faraday's law which is defined as the negative change is magnetic flux over time mulitplied by the number of turns on a coil and is defined mathematically thus;

    [tex]emf = -N\frac{\Delta(BA)}{\Delta t}[/tex]

    You will also need Ohm's law;

    [tex] V = IR[/tex]

    Can you go from here?

    -Hoot :smile:

    If you need a derivation of Faraday's law, you can do a search on the net or I'm happy to guide you through it here.
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