How Does Current Affect Magnetic Field at the Center of Two Wires?

[ttiger2k7]

[SOLVED] Magnetic Field of Two Wires

Homework Statement

http://img80.imageshack.us/img80/5625/jonesj2qm4.gif

If r = 30.0 mm, i = 2.00 A, and i' = 8.60 A, what is the magnitude of the magnetic field at the center point?

Homework Equations

B=(\mu_{0}I)/(2pi*r)

The Attempt at a Solution

I applied biot-savart's law to i and i', and added them together.

For B_i:

(4pi*10^-7*2)/(2pi*.03) = 1.34*10^-5

For B_i':
(4pi*10^-7*8.6)/(2pi*.03) = 5.74*10^-5

B_center = B_i + B_i' = 7.08*10^-5

Which is not correct. I'm pretty much sure my method at solving the problem is completely wrong. I just don't know what exactly is the right steps to take. Any help would be appreciated.

 

[jlg]

biot-savart for a loop is u*2*pi*I/4*pi*R, which simplifies to u*I/2*R.. you're only looking for half a loop so 1/2 * that is equal to u*I/4*R ..

The total mag field would thus be: u*I'/4*R + u*I/4*R

u = 4*pi*10^-7, by the way.

 

[ttiger2k7]

Ah, thanks! Got it.