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Physics Question on Magnetic Field

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 line XX' is given by

A

B

C

D

Answer

Explanation

Solution

If the current flows out of the paper, the magnetic field at points to the right of the wire will be upwards and to the left will be downwards as shown in figure
Now, let us come to the problem.
Magnetic field at C = 0
Magnetic field in region BX ' will be upwards (+ve) because all points lying in this region are to the right of both the wires
Magnetic field in region AC will be upwards (+ve), because points are closer to A, compared to B. Similarly magnetic field in region BC will be downwards (-ve).
Graph (b) satisfies all these conditions. Therefore, correct answer is (b).