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Quick question on force direction Please help!

  1. Aug 8, 2011 #1
    Quick question on force direction....Please help!

    1. The problem statement, all variables and given/known data
    A 550 - turn solenoid is 12 cm long. The current into it is 36 A. A 3.6 cm long straight wire cuts through the center of the solenoid, along the diameter. This wire carries a 26 A current downward (and is connected by other wires that don't concern us).

    Part A: What is the force on this wire assuming the solenoid's field points due east?

    Part B: to the east; to the north; to the south or to the west

    2. Relevant equations
    B = mu(0) * (N/L) * I
    F= I * L * B

    3. The attempt at a solution
    I was able to use the (relevant) equations to find the answer for Part A. It was: F = 0.19 N. However, I'm having trouble figuring out the directions of certain fields. I know there are things like the right hand rule; but I can't seem to conceptualize a 3D visual of how it works; in my head. Please help!
     
  2. jcsd
  3. Aug 8, 2011 #2

    BruceW

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    Re: Quick question on force direction....Please help!

    The rule is that for a flow of positive charges, if your index finger points in the direction of current, and if your middle finger points in the direction of magnetic field, then your thumb will give the direction of the force.

    It is electrons which flow through a wire, which are negatively charged, so the direction of the force will be made opposite to the rule above (if you're using the true current). But if you use conventional current, then the original rule applies.

    In either case, the force will be exactly perpendicular to both the magnetic field and the current.
     
  4. Aug 8, 2011 #3
    Re: Quick question on force direction....Please help!

    Thanks, I think I have a better grasp on the concept. So for this problem the force points to the south.
     
  5. Aug 8, 2011 #4

    BruceW

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    Re: Quick question on force direction....Please help!

    Yes, that's right.
    Unless specified otherwise, 'current' usually means 'conventional current'. (Which is what I assume they meant in this question).
     
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