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Lenz's Law explanation

  1. Mar 17, 2007 #1
    i am having so much difficulty understanding lenz's law.

    i don't know what it means and how to use it.

    will someone please give me a good explanation for it because my book SUCKS and i'm having a very hard time understanding this hard(and stupid) topic so please help me.
     
  2. jcsd
  3. Mar 17, 2007 #2

    jtbell

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    Staff: Mentor

    Can you give us one of the examples that your book uses for Lenz's Law and tell us what you don't understand about it? Then perhaps someone can give you an explanation that's more likely to help you, rather than giving a general explanation that might just repeat what you've already seen (and don't understand).
     
  4. Mar 18, 2007 #3
    Lenz's Law states that in a given circuit with an induced EMF caused by a change in a magnetic flux, the induced EMF causes a current to flow in the direction that opposes the change in flux. That is, if a decreasing magnetic flux induces an EMF, the resulting current will oppose a further decrease in magnetic flux. Likewise, for an EMF induced by an increasing magnetic flux, the resulting current flows in a direction that opposes a further increase in magnetic flux.

    It is important to note that the induced current will always flow in a direction which opposes any change of magnetic flux, but it does not oppose the magnetic flux itself.

    Lenz's law can be derived from Faraday's law of induction, simply by noting the minus sign on the right side of the equation. How Lenz got his name in history for this is beyond me!

    Lenz's law states that "direction of induced EMF is opposite to very cause producing it"
    In the case of an inductor coil where the electric wire makes N turns, the formula becomes:
    e = -N dΦ/dt

    where e is the induced electromotive force and dΦ/dt is the time-rate of change of magnetic flux Φ.
     
  5. Mar 18, 2007 #4
    How about this, a loop of wire absolutely hates having its magnetic flux changed. It will do everything it can to try to keep it the same, i.e. induce a current, and thus a magnetic field to replace the old one, or counter the new one. Lenz's law tells you which way to point your thumb to figure out the current direction. If it's losing flux, point your thumb in the direction it was pointing to restore it. If it's gaining flux, point your thumb against it to oppose it.
     
  6. Mar 18, 2007 #5
    people always always have major trouble with lenz' law. ive never really been able to get it myself unless i can figure out the direction of the chane in flux.
    often times people can not even understand clockwise and counterclockwise. which admittedly is arbitrary and confusing because it is relative. people understand into the page and out of the page or left and right but CCW and CW are confusing. it depends on how you look at your hands like from which vantage point.
    but i do have a question.
    why does the wire "hate" having its magnetic flux or flow of direction of current change? I mean why should it care?

    this website helped me a lot to learn Lenz Law

    http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/MagneticField/LenzLaw.html
     
    Last edited: Mar 18, 2007
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