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Homework Help: Direction of magnetic forces

  1. Mar 14, 2012 #1
    1. The problem statement, all variables and given/known data

    Two long parallel wires A and B. They are shown from a plane perpendicular to the wires.
    There is a point P with some distance "d". This creates an "L" shape if you play connect the dots and look down on the paper.

    1)What is the magnetic force on wire B if only A carries a current?

    In this scenario the current in wire A is headed into the paper or away from me when looking down. Using the RHR this means my fingers are curled clockwise.

    2)What is the magnetic force on proton P traveling to the right(in the direction of B) if only wire A is carrying a current.

    In this scenario the current in wire A is headed out of the paper or towards me when looking down. Using the RHR this means my fingers are curled counter-clockwise.



    3. The attempt at a solution

    1) I figured, from using the RHR, that the field at B from A points down, tangent to the circular magnetic field lines(again looking down at the paper). Since only wire A has current running through it and none through wire B that there shouldn't be any force exerted on wire B(at least i believe so). If there was current running through wire B then the force on B would either attract or repel from A depending on current direction. My answer is there is no force on B or zero force.

    2)I have no clue how to work this(well i'm not confident if i do know) but if i were to try and give it a go, I would have to say that the force on the proton is going to point towards the direction the current flows which is out of the paper in this scenario. I figured i'd use the RHR yet again.

    Any help(if wrong) or a clearer understanding(if right) would be nice.
    Thanks.
     
  2. jcsd
  3. Mar 15, 2012 #2

    PeterO

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    Homework Helper

    Don't you need a current in both wires to get an induced force?
     
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