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Homework Help: Charge in a Magnetic Field question

  1. Dec 6, 2016 #1
    1. The problem statement, all variables and given/known data


    These are two similar questions, one from my previous exam and one from a sample test my teacher provided. I understand how to work the problem, but my question is how is the i or j component decided in each of these?

    2. Relevant equations

    From our formula sheet...

    3. The attempt at a solution
  2. jcsd
  3. Dec 6, 2016 #2


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    There is a coordinate system provided that gives the direction of the unit vectors. The direction of the force on charge q (assuming it is positive) is the same as the direction of the induced current at the position of the charge if the dotted circle were a circular metal loop. The induced current can either be clockwise or counterclockwise. This eliminates all the ## \hat{j}## options in the first picture and all the ##\hat{i}## options in the second picture. The sign depends on whether you have clockwise or counterclockwise current flow. Can you figure that out?
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