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Homework Help: Electromagnetic Induction

  1. Aug 29, 2009 #1
    http://img30.imageshack.us/img30/7309/coil.png [Broken]
    The figure shows a coil of wire in xy-plane with a magnetic field along y-axis. Around which of the three axis should the coil be rotated in order to generate emf and current in the coil?

    I think the answer is X and Z AXES because in these cases the plane of the coil (or the coil?) is
    perpendicular to the magnetic field.
    Please confirm this.....
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Aug 29, 2009 #2


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    First, this question should really be in the homework section.

    Second, think about Faraday's Law.....a changing ___?___ produces an emf....When you rotate the coil around the z-axis does the ___?___ through the coil change? How about around the y-axis? Around the x-axis?
  4. Aug 30, 2009 #3
    Achanging magnetic flux produces an emf...

    Well, if the ring is rotated around y-axis, the coil will definitely be parallel to the magnetic field so [tex]\epsilon[/tex]=vLBsin0=0
    The opposite will happen if rotated around x-axis, [tex]\epsilon[/tex]=vLBsin90=vLB

    But what if the coil is rotated around z-axis?
  5. Aug 30, 2009 #4
    in an abstract view, nothing will happen if rotated about z-axis, the coil is still parallel to the magnetic field and no change in flux is made, so no current induced, however if we considered the coil's thickness there will be some eddy currents perpendicular to the flux direction.
  6. Aug 30, 2009 #5
    so rotating about the z-axis means the ring/coil is actually spinning??
  7. Aug 30, 2009 #6


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  8. Aug 30, 2009 #7
    hmmm..that clears it thanks!
  9. Aug 30, 2009 #8
    so what's the answer?
  10. Aug 30, 2009 #9
  11. Aug 31, 2009 #10
    An emf will not be induced in the coil if it rotates around the y axis. This is because the flux linked to the coil is the dot product of its area and the magnetic field. As the coil rotates about the y axis the angle between its area (normal to the plane of the coil) and the magnetic field remains at 90 deg. Hence the flux linked to the coil correspondingly remains zero during the rotation, and therefore the induced emf is zero.
    Thus the answer to the problem is rotation about the x axis only as already clarified. The above is only to elaborate further on the impact of rotation about the y axis.
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