Physics Question? need some help.?

Question

I'm having problems with part B of this problem. Any help anyone can give me would be greatly appreciated. Please see below:

Two long, straight wires are separated by 0.12 m. The wires carry currents of 5.5 A in opposite directions, as the drawing indicates.

http://www.webassign.net/CJ/21_56.gif

(a) Find the magnitude of the net magnetic field at the point A.
Answer is 2.9333e-5 T

(b) Find the magnitude of the net magnetic field at the point B. (in T)

It was my belief that the fields should cancel each other out and the magnitude should be 0 T at point B, but the answer is wrong when I submit it. Am I missing something?

Answer 1

They do not cancel each other out. Magnetic field vectors B of both wires are equal: they point downward and perpendicular to the plane of both wires. (Remember that the field is oriented according to the right-hand rule; use it for both currents and you will see. It is best if you draw the situation as it is on the plane that is perpendicular to the plane of both wires.)
Then, use the equation for magnetic field of the current wire:
B = μ0 x I / 2πr. Since point B is at the middle, both wires produce the field with the same magnitude and we have to multiply the equation with 2. We get:
B = μ0 x I / πr = 4π e-7 Vs/Am x 5.5 A / (π x 0.060 m) = 3.6e-5 T

Answer 2

At point B the two fields are equal and same direction. The distance vectors are are opposite and the currents are opposite. The two taken together mean that the fields add.