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Direction of Current

  1. Feb 29, 2008 #1
    [SOLVED] Direction of Current

    1. The problem statement, all variables and given/known data

    I am having problems identifying in which way the induced current for a loop will be.

    Code (Text):
    A loop is placed in a magnetic field as shown in the figure.
    If the magnitude of the field is decreased, the induced current
     in the loop will be.
    [​IMG]

    with the following options:

    Code (Text):

    A) out of the page.
    B) clockwise.
    C) into the page.
    D) counter clockwise.
     
    2. Relevant equations

    Right Hand Rule

    3. The attempt at a solution

    Well I tried using the right hand rule. I have learned that the x's represent that the current is flowing into the wire, away from me. So I placing my thumb facing away from me, and my finger curl, and it seems to be going out of the page. Also, how do I know if I should turn counterclockwise or clockwise?
     
  2. jcsd
  3. Feb 29, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The x's represent the direction of the magnetic field, which is into the page.
    To use the right hand rule like I do, just make a fist with your thumb pointing up. Like you're making a "thumb's up" gesture.

    Here's a picture (look at the right-most hand diagram in the middle): Right Hand Rule

    But first you must understand Faraday's law and Lenz's Law. The induced current always goes in a direction that opposes any change to the flux through the loop.
     
  4. Feb 29, 2008 #3
    so it is going out of the page.

    I tried the right hand rule, pointing into the "page", made the counter clockwise turn and it would be into the page, and since the induced current goes against the magnetic field.
     
  5. Feb 29, 2008 #4

    Doc Al

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    Staff: Mentor

    The current flows in the loop. It's either clockwise or counterclockwise.

    In what direction is the flux changing? What current is needed to oppose that change?
     
  6. Feb 29, 2008 #5
    I think I know what you are trying to say. We need the current to go into the page, and using the right hand rule that would be going clockwise. We need a current going outwards to oppose the inward force.
     
  7. Feb 29, 2008 #6

    Doc Al

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    Staff: Mentor

    No.

    In this problem, the field points into the page and is decreasing. Therefore the induced current will act in such a way as to increase the field into the page. Which direction of current will produce a field that points into the page?
     
  8. Feb 29, 2008 #7
    it will point in the direction of the field to keep it constant., the diagram in hyperphysics also shows an arrow pointing down, which must mean, clockwise.
     
  9. Feb 29, 2008 #8

    Doc Al

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    Staff: Mentor

    Careful with how you describe things. The current does not point in the direction of the field. You need a current that creates a field pointing into the page. Using the right hand rule, a clockwise current is needed to generate such a field.
     
  10. Feb 29, 2008 #9
    oh, I thought the current was the one points, we were trying to find a current that created a field pointing inwards. Thank you for your help and patience.
     
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