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Two long straight wires are parallel and 7.8 cm apart. They are to carry equal currents such that the magnetic field at a point halfway between them has magnitude 340 µT. (a) Should the currents be in the same or opposite directions? (b) How much current is needed? (a) (b) Number Units

In the figure, four long straight wires are perpendicular to the page, and their cross sections form a square of edge length a = 15 cm. The currents are out of the page in wires 1 and 4 and into the page in wires 2 and 3, and each wire carries 23 A. What is the magnitude of the net magnetic field at the square's center? 2 Number Units a 3 ·x