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Electromagnetic induction and Lenz's law

  1. Apr 22, 2008 #1
    Actually am learning Lenz's law but am just getting confused.i know that the change of a magnetic field around a solenoid creates electricity. meaning that when we move the north pole of the magnet towards the end of the solenoid, the galvnometer deflects in one direction and when we move it away from the galvanometer, this one will deflect in the opposite direction.
    Now my question is: we don't change the end of the solenoid but we change the magnet poles. Now if we use the south instead of the north, is the generated current in the same direction as the one generated in the first case? why?
    thank you!
  2. jcsd
  3. Apr 23, 2008 #2


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    Lenz's law states that current will flow in a direction to oppose the change in magnetic flux. Thus, if you switch the magnet around and instead move the south pole, the opposite will happen. (Moving towards the solenoid with the South pole will cause the opposite deflection as moving towards the solenoid did with the North end)
  4. Apr 23, 2008 #3
    It's terrible the way I imagine personality in inanimate objects, but the way I have always used Lenz's law is -- The coil says to itself: "I want to make that magnet's job more difficult. What magnetic field would I have to create in order to repel the magnet that's moving toward me, or to attract the magnet that's moving away from me? After I have answered that, what direction of current would I need, in order to produce such a magnetic field?"
  5. Apr 24, 2008 #4
    Wow what a cute imagination. Thank you a lot, i think i ll never be confused no more with this way of thinkin! Now i got it
  6. Apr 24, 2008 #5
    It has to be difficult to move the magnet, regardless of which way you're moving it, because the magnet has to be required to overcome a force, so that it will have to do work in order to move. Then the work that the magnet does will be equal to the electrical energy that comes out of the coil. If you got electrical energy out, and the magnet didn't have to put work in, conservation of energy would be violated.
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