# Magnetic field of two parallel wires with opposite current

1. Two parallel wires, each carrying a current of I = 3.1 A, are shown below, where d = 5.2 cm. The current in wire 1 is in the opposite direction of wire 2. Find the direction and magnitude of the net magnetic field at points A, B, and C.

See attached file for full problem description.

I don't know how to do the problem - I have to convert Telsas to μT, and when I did that, using Ampere's law for long, straight wires, I got 11.36μT, into the page for both points A and C, but they were wrong. I don't understand what equation I am supposed to use. I really need to know how to find the direction of the magnetic field as well.

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#### Solution Preview

Magnetic field of a rectilinear current (current in an infinite straight wire) I at distance R from the wire has magnitude

B = μo I / (2 π R),

where the magnetic permeability of vacuum is μo = 4π x10-7 m kg C-2.

I suppose you have this formula in your books as well as the explanation on the direction.

In particular, for Wire 1, the direction of its magnetic field at the given points is:

A: into the page

B and C: out of the page

For Wire 2, the directions ...