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How to find direction of mangetic field created by current

  1. Aug 7, 2011 #1
    how to find direction of magnetic field created by toroid

    I don't understand how to find the direction of B resulting from a toroid. In the following example from my textbook, the direction of B is found by symmetry arguments are used. (I highlighted this in yellow). Could someone please explain?
    Thanks!

    8e6d269a.png
     
    Last edited: Aug 7, 2011
  2. jcsd
  3. Aug 7, 2011 #2

    Delphi51

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    Homework Helper

    The symmetry argument does not address direction; it merely means the field is the same all around the loop because rotating the loop a few degrees does not change the situation.

    The direction is determined by the hand rule. This page has it in the very first diagram:
    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html#c1
    I urge you to find a piece of wire and make a toroid. Then choose a spot on it and wrap your hand around it with your thumb in the direction of the current. Your fingers indicate the direction of the B field. It will go one way inside the coil, the opposite way outside it.
     
  4. Aug 8, 2011 #3
    Thanks! :)
     
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