Question

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

opposite

(b) How much current is needed?

Answers

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

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