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Homework Help: Electricity/Magnetism help

  1. Mar 3, 2004 #1
    Hello, I've done all of the calculations on my homework assignment and have gotten what seem to be the mathematically correct answers, but I'm not sure that they logically make sense. This is the diagram and the problem:

    You are standing on train tracks in such a way that a circuit is completed. You have a lamp in your hands that has an internal resistance of 45 ohms. The track rails are 1.2 meters apart and the magnetic field is coming out of the page with a magnitude of 10^-5 Tesla. There is a train approaching at a velocity of 300 m/s. Find the current in the circuit, the total power used in the circuit and the force exerted on the train.

    So I calculated the voltage with the equation "emf = Blv". Is this correct? For an answer, I got 3.6 X 10^-2 V.

    To find the current, I used the proper form of "V = IR" and got an answer of 8.0 X 10^-4 A.

    In order to calculate the power, I used "P = VI" and used the Voltage and Current values that I had already calculated.
    This yielded 2.88 X 10^-5 W.

    Finally, I calculated the force using the proper form of the equation "P = Fv".
    This required me to divide 2.88 X 10^-5 by 300, giving me 9.6 X 10^-8 N. I might not be thinking about this correctly, but that seems a bit small. Did I screw up somewhere?

    Thank you, in advance.
  2. jcsd
  3. Mar 3, 2004 #2

    Doc Al

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    Staff: Mentor

    Your methods look good to me. I think you did make a decimal point error in calculating the emf, which carries through to the other numbers.
  4. Mar 3, 2004 #3
    Thank you very much, especially for pointing out the error in my math. That's a big help.
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