Question

Two long straight parallel wires are a distance 2 d part. They carry steady equal currents flowing out of the plane of the paper. The variation of magnetic field B along the line xx’ is given by

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is B

For two parallel wires carrying currents in opposite directions, the magnetic field at any point along the line joining them will have a characteristic variation. According to Ampère's law, the magnetic field due to each wire at a distance \(r\) is given by: \[ B = \frac{\mu_0 I}{2\pi r} \] Where:
\(B\) is the magnetic field,
\(\mu_0\) is the permeability of free space,
\(I\) is the current in the wire,
\(r\) is the distance from the wire. Along the line \(xx'\), the magnetic field at points between the wires will oppose each other due to the opposite directions of current.
Hence, the magnetic field will vary as shown in option (B), with the field strength decreasing towards the center and increasing as we move away from it.

The correct answer is (B) : .