Two long parallel wires are at a distance 2d apart. They carry steady equal current flowing out of the plane of the paper as shown. The variation of the magnetic field 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)`.