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Magnetic field

  1. Oct 2, 2008 #1
    when a charge moves in magnetic field a force perpendicular to velocity and B acts on charge then why the charge do not move in the direction of that force
  2. jcsd
  3. Oct 3, 2008 #2
    it does. where did you get the idea that it doesnt?

    well in one sense it doesnt move 'through' the force because the force is always at a right angle to the motion of the particle. so the particles direction changes but its speed doesnt change.
  4. Oct 13, 2008 #3


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    Welcome to PF!

    Hi nikhilthunder! Welcome to PF! :smile:

    ("why does the charge not move in the direction of that force" :wink:)

    From Newton's second law, force = mass times acceleration …

    so the acceleration is always in the direction of the force …

    but in circular motion, the acceleration is centripetal (towards the centre of the circle), so the charge carries on moving perpendicular to the force. :smile:

    (and, as granpa says, the speed doesn't change … so the energy doesn't change … this is because of the work-energy theorem … work done = change in energy, and work done is zero because the force is perpendicular to the motion :wink:)
  5. Oct 13, 2008 #4
    There is a Force (vector) F= qV x B (where V and B are vectors) I seem to remember that from many years ago...anyway, the force IS "sideways" via the right hand rule.

    Is that the relationship you are questioning???
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