Anyone see where I messed up on finding the current?

[mr_coffee]

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!

 

[Chi Meson]

check "r." What is this distance supposed to be?

 

[BerryBoy]

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

 

[mr_coffee]

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]

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

 

[mr_coffee]

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 each other, and the currents are equal

 

[Chi Meson]

Part of the question is to decide which way the currents must run, parallel or antiparallel. One way will cancel the fields, the other way will add up the fields. Use the right hand.