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Homework Help: EMF induced

  1. Jun 26, 2008 #1


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    1. The problem statement, all variables and given/known data

    http://img164.imageshack.us/img164/3313/qqqqo3.jpg [Broken]

    Find the total magnetic flux through the coil at t=0
    Given that the rate of change of flux at any time,t, is equal to [itex]2 \pi f \phi sin 2 \pi ft[/itex], find the maximum instanteous value of the induced emf at any time & the rms value of the induced emf.

    If the coil were fixed and the magnet rotated at the same rate in the same direction, what difference would this make in the induced emf?

    2. Relevant equations

    3. The attempt at a solution

    [tex]\phi = NBA = (150)*(4 \times 10^{-4})*( \pi (\frac{0.1}{2})^2)= 4.7 \times 10^{-4}Wb[/tex]

    Max emf at any time.

    [tex]E=2 \pi f \phi sin 2 \pi ft \Rightarrow E_{max}=2 \pi f \phi = 2 \pi (25)(4.7 \times 10^{-4})=0.074V[/tex]

    [tex]E_{RMS}= \frac{0.074}{\sqrt{2}}=0.052V[/tex]

    and No change in the emf.

    Any part wrong?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jun 26, 2008 #2


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    If the magnet rotates in the same direction about a fixed coil, then the relative direction of rotation of the coil in the magnetic field is reversed. That won't change the magnitude of the induced emf, but... (I'm not clear as to whether the question is asking only about quantitative differences...)

    I concur with your calculations.
    Last edited: Jun 26, 2008
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