# Anyone see where I messed up on finding the current?

I'm not sure what i'm doing wrong...
Two long straight wires are parallel and 5.0 cm apart. They are to carry equal currents such that the magnetic field at a point halfway between them has magnitude 320 µT.

(a) Should the currents be in the same or opposite directions?
same
opposite
correct check mark
(b) How much current is needed?
wrong check mark A

Here is my work:
http://show.imagehosting.us/show/916283/0/nouser_916/T0_-1_916283.jpg

Thanks!

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Chi Meson
Homework Helper
check "r." What is this distance supposed to be?

Consider that one wire should be producing HALF of the field...
I Agree with Chi... Check your r value.

I did what i think u guys ment....since its only half way, I took half the distance .05m, which is .025, and i plugged it into the formula:
(B*2PI*r)/u = i;
i = (320E-6)(2*PI*(.025)/1.26E-6
i = 39.89 which was also wrong
is that what u guys ment?

lightgrav
Homework Helper
don't you have two wires? Both contribute the the B-Field.

So is the mangintude of the b field just multiplied by 2? or would it be 0? because they are producing a repulisve force on eachother, and the currents are equal

Chi Meson