Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Induced EMF, finding current

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data

    A coil with 253 turns of wire, a total resistance of 28 Ohms, and a cross-section area of 0.36m^2 is positioned in a plane perpendicular to the field of a powerful electromagnet.
    What average current is induced in the coil during the 0.33s that the magnetic field drops from 2.2T to 0.0T? Answer in units of A.

    2. Relevant equations

    E = BA / t
    V = IR

    3. The attempt at a solution

    EMF = Change in B * Area / time
    = (2.2 * .36) / .33

    I plug that into V = IR

    V = IR
    [(2.2 * .36) / .33] = I * 28 Ohms
    I = [(2.2 * .36) / .33] / 28 = 0.0857142857A

    However I get the wrong answer.
    I think it has something to do with the 253 coils of wire but I'm not sure.
    Any help is appreciated.
  2. jcsd
  3. Mar 23, 2010 #2
    Yes, the emf you calculate is induced in each coil of wire, so the total flux linkage at the start is BAN where N is the nuber of turns.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook