Electromagnetic induction problem

  1. 1. The problem statement, all variables and given/known data

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    http://imageshack.us/photo/my-images/194/55132039.png/

    How much curret flows trough circuit ABCD when the center of the circuit (O) is distance r from the straight wire?


    I think these are the relevant equations:
    ∅=B.dS
    E=-d∅ /dt
    B= μoI/2∏r

    But i have trouble with dS. i know that is has to be rewritten like e.g. ds= ydx=yvdt and that way eliminate dt
    but in this case i dont know how to do it.

    Thanks
     
  2. jcsd
  3. rude man

    rude man 5,809
    Homework Helper
    Gold Member

    Well, obviously v is associated with dψ/dt where ψ = ∫BdS (apperently you are using S for area.) (Sorry, the symbol table does not have a Greek letter for "phi", can't imagine how that fell thru the cracks).

    You have the right formula for B(r), you know v = dr/dt, right? So how does ∫BdS change with time? S doesn't change with time, it's just the area of the square .... so it must be B that is changing ...
     
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