Two long straight wires are parallel and 9.0 cm apart. They are to carry equal currents such that the magnetic field at a point halfway between them has magnitude 320 µT.

Question

(a) Should the currents be in the same or opposite directions?

opposite

(b) How much current is needed?

Answer 1

a) If the currents were in the same direction in both wires, they would cancel in the middle

b) Use Ampere's law and double the field of a single wire

Answer 2

The current must be in the opposite direction if it has to produce some megnatic field B. B=ui/R