Strength of the magnetic field around a wire?

Question

Three parallel wires are arranged in a partial square configuration as shown in the diagram. In two of the wires, a 5.00×10−4 A current flows toward you, and in the third wire a 7.50×10−4 A current flows away from you. What is the strength of the magnetic field at the point P, at the "missing corner" of the square?

See diagram.

http://i338.photobucket.com/albums/n418/gregismighty/p8e.jpg

Answer 1

Use the right-hand-rule for each wire to find the direction of B; right thumb in direction of current, fingers curl in direction of B.  You'll see that the magnetic fields for the two wires directed toward you (let's call these fields B1 & B2) intersect pt. P such that their resultant (B(1,2)) will be 45˚ from vertical.  You'll also see that the field for the other wire (B3) will intersect pt. P at 180˚ in the opposite direction.  That shows B3 is subtracted from the resultant of B1 & B2.

Use Ampère's Law to find the magnetic field:

B1 = [(μ0*i)/(2*π*r)]

B2 = [(μ0*i)/(2*π*r)]

B3 = [(μ0*i)/(2*π*r)]*cos45˚

(r for B1 and B2 will be .0536m, but r for B3 will be the hypotenuse of a square w/ sides of .0536m)

Find the resultant of B1 & B2 (Pyth.Thm):

B(1,2) = sqrt(B1² + B2²)

And B(net) at point P will be B(1,2) - B3.

[μ0 = 4π×10^-7 (T*m)/A]