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Electromagnetic forces

  1. Aug 28, 2009 #1
    Speed = distance/time and current = charge/time. Explain how F=BIl is actually the same equation as F= Bqv but considered for many charges in a group?

    can someone please explain with working out please?

  2. jcsd
  3. Aug 28, 2009 #2
    Lets say that you had a wire with a length l. Lets say that traveling through that length is a net charge q, with an average velocity of v. v = distance/time, in which in this case, v = l/t. The current is I = charge/time = q/t. Therefore, F = B*q*(l/t) = B*(q/t)*l = BIl.
  4. Aug 30, 2009 #3
    thanks a lot!
  5. Aug 31, 2009 #4
    For clarity, these two equations (part of the Lorentz Force Law) are written as

    F = l(I x B) = q(v x B)

    where x indicates the cross product. meaning that the vectors F,I and B; or F,v,and B are all mutually orthogonal.
  6. Aug 31, 2009 #5


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    The I/v vectors need not be orthogonal with the B vector.
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