Magnitude of magnetic field

Question

two long insulated wires lie in the same horizontal plane. wire A runs north-south, and Wire B runs east-west. a current of 20.0 A flows in wire A towards the north and a current of 10.0 A flows in wire B towards east. what is the magnitude and direction of the magnetic field at a point that is 5.00 cm above the point where the wires cross?

Answer 1

Use Ampere's law to calculate the B field for each wire and then add them vectorially.

For wire A

B = (u0)I/(2pi)r = 8 x 10^-5 T east

For wire B

B = (u0)I/(2pi)r = 4 x 10^-5 T south

B(net) = sqrt(8^2 +4^2) x 10^-5= 8.9 x 10^-5 T

arctan(.5) = 26.6degrees  south of east

Answer 2

ah, crud- yea my bad, I was thinking inside the plane on this one, the 5 cm points the the region orthogonally outside of the horizontal plane that makes sense too. Thought it meant 5cm north of the intersect within the plane, yea the guy under me got it.

Don't report this, just ignore it