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Homework Help: Finding direction of induced current

  1. May 9, 2014 #1
    1. The problem statement, all variables and given/known data
    The right side of a wire loop is dragged to the left across the south pole of a magnet. What will be the direction of the current induced in the loop?

    a. No current will flow around loop.
    b. Current will move in the wires of the loop in the same direction as the loop itself.
    c. Current will move in the wires of the loop in the opposite direction as the loop itself.
    d. Current will oscillate back and forth around the loop (AC current)
    e. Current will flow clockwise around the loop.
    f. Current will flow counter-clockwise around the loop.

    2. The attempt at a solution
    Because of the right hand rule, would the current be moving counterclockwise (f)?

    Also does the magnetic field point to the right?

    What difference does it make when the right side is dragged vs the left side?

    Also, why does a down direction of t he current cause a clockwise current throughout the loop as opposed to a counterclockwise current?
    How do you know if the current will move in the wires or around the loop? Can I eliminate b and c because an induced current involves moving a loop over a magnet?
    Please help, I'm very confused!
    Last edited: May 9, 2014
  2. jcsd
  3. May 9, 2014 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    The answers depend on what is meant by "right side" etc.
    These descriptions seem to be specific to your course.

    The rule you want is that the current will flow so as to set up a magnetic field that opposes the motion of the magnet.

    Moving the loop one way is the same as moving the magnet the other way.

    So - if you have a loop in the x-y plane, centered at the origin, so is follows x^2+y^2=r^2 and r is the radius of the loop...

    Looking down the +z axis at the loop, a magnet placed in position z>0 will be "above" and if it moves from -x values to +x values, then it moves from left to right.

    If it goes south-pole downwards, then the magnetic field is pointing "upwards".
    As the magnet crosses into the loop, the field inside the loop gets "more south".
    What pole is needed to oppose that motion?
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