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Doubt in Lenz's Rule

  1. May 20, 2013 #1
    I have certain doubts with Lenz's Law. Now, consider a horizontal loop. If a magnet with N facing the entrance of the loop is moving towards the loop. By Lenz's, Flux has increased. Who has increased it. The magnet. We oppose the downward B by inducing the UPWARD B. Thus, I is clockwise (RHR). Now, consider a generator initially horizontal (inline) with a West-East B. It rotates clock-wise. What is the direction of E? Who created the change? The movement clockwise. So we oppose the FORCE now. And by RHR, the I is also clockwise. Now my question is does Lenz's Rule tell us about opposing the FORCE of THE MAGNETIC FIELD? What if both occur at the same time? Consider the magnet is still and we move the loop. Do we oppose the loop movement by a FORCE or MAGNETIC FIELD?

    Thanks for Helping in advance!
  2. jcsd
  3. May 21, 2013 #2


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    Why do you want to make a distinction? The force is there because of the current in the loop - which is only there because of the presence of the field and the movement.
  4. May 21, 2013 #3


    Staff: Mentor

    Lenz's law is simply the negative sign in Faraday's law. Faraday's law deals only with the fields, not the forces. So wrt Lenz's law the change is opposed by the fields.

    Of course, as sophiecentaur correctly points out the distinction is rather academic since the Lorentz force equation also holds and always works out so that the force opposes the motion also. I.e. the specification of the opposition by the fields is a matter of semantics (the term "Lenz's law" refers to the fields), but physically the movement is opposed by both!
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