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Lorentz force and workdone

  1. Nov 2, 2008 #1
    From Lorentz force law,

    F = q (v х B) = q v B sin θ
    F = q v B [For θ = 90]

    W = F * d = F d cos θ
    w = 0 [For θ = 90]

    How come we have a force but no work done?
  2. jcsd
  3. Nov 2, 2008 #2
    Do you think work should be done? Work is done where the force has a component in the direction of the velocity.
  4. Nov 2, 2008 #3
    if w=0 then energy =0, then how the charge q goes at velocity v in field B.from where the charge q gets energy?
  5. Nov 2, 2008 #4


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    Not true. Counter-example: a particle sliding across a frictionless table with velocity v. There is no work being done, but then energy is non-zero.
    Perhaps, the charge was travelling at velocity v before it entered the magnetic field?
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