Question

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 1

Correct Answer - B
The wires at `A and B` are perpndicular to the plane of paper and current is towards the reader . Let us consider certain points .
Point C ( mid point between ` A and B`) : The magnetic field at `C` due to ` A( vec(B)_(ca))` is in upward direction .
Net field is zero .
Point `E` : magnetic field due to `A` is upward and magnetic field due to `B` is downward but
| vec(B)_(EA)| lt | vec(B)_(EB)|`.
:. Net magnetic field is in downward direction .
Point D : | vec(B)_(DA)| gt |vec(B)_(DB)|`. Net field upwards . similarly , other points can be considered.