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

Options

A.
B.
C.
D.

Answer

B

Explanation

If the current flows out of the paper, the magnetic field at points to the right of the wire will be upwards `&` 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.
Similarly
Magnetic field in region `AX` will be downwards `(-ve)`
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 anwer is `(B)`.