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Homework Help: Question regarding Magnetic field

  1. Jul 16, 2013 #1


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    Gold Member

    1. The problem statement, all variables and given/known data
    Let [itex]\vec{E}[/itex] and [itex]\vec{B}[/itex] denote electric and magnetic fields in a frame S and [itex]\vec{E'}[/itex] and [itex]\vec{B'}[/itex] in another frame S' moving with respect to S at a velocity [itex]\vec{v}[/itex]. Two of the following equations are wrong. Identify them.

    a)[itex]B_y ' = B_y + \dfrac{vE_z}{c^2}[/itex]
    b)[itex]E_y ' = E_y - \dfrac{vB_z}{c^2}[/itex]
    c)[itex]b_y ' = B_y + vE_z[/itex]
    d)[itex]E_y ' = E_y + vB_z [/itex]

    2. Relevant equations

    3. The attempt at a solution
    First of all I can't understand what is 'c' here. Is it speed of light?Also, how can the magnitude of field change with frame? The magnitude of force can vary but I don't think field should vary. This question seems too complicated to me.
  2. jcsd
  3. Jul 16, 2013 #2


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    Science Advisor

    ##c## is the speed of light yes. The magnetic and electric fields transform non-trivially under Lorentz boosts; one can prove this using special relativity. You can probably look it up online if you don't have a textbook that discusses it.
  4. Jul 16, 2013 #3


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    Staff: Mentor

    Dimensional analysis might be useful here.
  5. Jul 17, 2013 #4


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    Hmm... So its just basically a problem of dimensional analysis. No magnetics involved.
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