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lenz's law

Discussion in 'MCAT Study Question Q&A' started by destroyMCAT, Aug 7, 2011.

  1. destroyMCAT

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    If a loop enters a magnetic field that is going into the page, according to the lenz's law there would be a gain of magnetic field that is going out of the page.. and the current would be counterclockwise.

    So, using right hand rule.
    The velocity is going from left to right (thumb points that direction)
    fingers = magnetic field so it points out of the page
    and my force points down... which would cause an clockwise current. What am I doing wrong?:confused:
     
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  3. AugustMCAT

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    The new field opposes the change in flux. If you put a loop into a field, there is an increase in the magnetic field pointing into the page. So the new field must point out of the page. Don't use the 3 finger right hand rule. Just use the right hand rule of you grabbing the wire. If the field is coming out of the page, then your thumb must be pointing right, hence a counterclockwise current.
    The 3 finger right hand rule also confirms this. Your velocity which you said is left to right is essentially the current. Be consistent with your analysis. I like to have the magnetic field use the perspective of WITHIN the loop.
     
  4. destroyMCAT

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    Can you elaborate on this? thanks

    edit: How do you know when to use the grabbing the wire right hand rule vs the 3 finger one?
     
    #3 destroyMCAT, Aug 7, 2011
    Last edited: Aug 7, 2011
  5. AugustMCAT

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    You are asked for the magnetic field. Force is not in question here, so you don't need the 3 finger rule.

    Generally, I always use the center of the loop for my perspective of the magnetic field. You were correct in saying velocity is from left to right. This velocity IS CURRENT. The movement of particles. So left to right (on the bottom half, using the center of the loop as perspective) creates a counterclockwise current.
     

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