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Homework Help: Copper wire attached to the terminals of a cell

  1. Jan 25, 2010 #1
    A diagram shows a flexible copper wire attached to the terminals of a dry cell.

    A strong circular magnet, 12 mm in diameter, is attached to the side of the cell. The interaction between the current in the wire and the magnetic field of the magnet causes the wire to levitate

    i.e.
    _____+
    l
    l [s n]
    l____ -

    The dashed and straight lines represents the copper wire attached to the 2 terminals, with a magnet attached in the middle of the cell.

    Now the same thing is given, but the magnet reversed, as well as the terminals:

    _____-
    l
    l [N S]
    l____ +

    Explain what would happen to the wire in the following arrangement.

    The answer is:

    Wire would levitate again
    Two reversals cancel/applying Flemings Left Hand Rule

    I dont understand what this means?
     
  2. jcsd
  3. Jan 25, 2010 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi Masafi! :smile:

    If you use the Left Hand Rule, and point two of your fingers in the opposite directions, your third finger will stay in the same place. :wink:
     
  4. Jan 25, 2010 #3
    Thanks, so how do I apply that here? Which finger is pointing where?
     
  5. Jan 25, 2010 #4

    tiny-tim

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    You tell us

    what is Flemings Left Hand Rule? :smile:
     
  6. Jan 25, 2010 #5
    I know what it is, but I dont get how you apply it here. The direction of current is known (+ to -) , but force and the direction in which B field applied is not given?

    How does this relate to the previous arragement?

    What I can think is using the direction of B field to be from N to S pole, so that would mean force acts down in the initial arrangment, as well as the 2nd one...
     
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