Two long parallel wires are at a distance 2d apart. They carry steady equal currents flowing out of the plane of the paper, as shown. The variation of the magnetic field B along the XX’ is given by
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Two long parallel wires are at a distance 2d apart. They carry steady equal currents flowing out of the plane of the paper, as shown. The variation of the magnetic field B along the XX’ is given by

G1 Physics · Accepted Answer

For each wire, B=μ₀I/(2πr) and changes sign on crossing the wire. Along XX′ the field diverges at the two wire positions, is zero at the midpoint by symmetry, and has the sign pattern shown only in graph B. Therefore B.