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Why is the magnetic field stronger at this specific point?

  1. Nov 17, 2008 #1
    A rod (shown in the picture on the link) rotates around the point O in a magnetic field. It is said for sure that the induced EMF in the rod is larger at point R compared to point P. Why's that?

    The picture: http://img58.imageshack.us/my.php?image=physicskx4.png
  2. jcsd
  3. Nov 17, 2008 #2
    The EMF is larger because the area of the enclosed circuit is larger. The magnetic field is NOT larger, it is constant.
  4. Nov 17, 2008 #3
    Oh I meant the EMF of course. But can you please explain your answer more thoroughly I don't fully understand the situation.
  5. Nov 17, 2008 #4
    The EMF is given by:
    [tex]\epsilon = \oint \left( \textbf{v} \times \textbf{B}\right) \cdot d\textbf{l}[/tex]
    Here, B is the magnetic field, dl is a small segment of a circuit, and v is the velocity of a charge in that circuit.

    If you think of the electrons in the rotating rod as charges going around in a circular circuit, then you can easily see why the EMF is larger when you get further from the origin.
    First of all, the velocity v is larger, secondly the path of integration (the length of the loop) is larger.
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