
#1
Jul2312, 05:57 PM

P: 9

1. The problem statement, all variables and given/known data
http://imageshack.us/photo/myimages/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
Jul2412, 08:37 PM

HW Helper
Thanks
PF Gold
P: 4,438

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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