Question

Three long straight wires A, B and C are carrying currents as shown in figure. Then the resultant force on B is directed :

• A. perpendicular to the plane of the paper and outward
• B. perpendicular to the plane of the paper and inward
• C. towards A
• D. towards C

Answer 1

The correct option is D towards C

Magnetic field due to C=$\frac{{\mu }_0\times 3}{2\pi d}$ into the plane.

Thus force due to this magnetic field on wire B=$F_C=BiL$

$\frac{{\mu }_0\times 3}{2\pi d}\times i\times L$ towards the wire C

Magnetic field due to A=$\frac{{\mu }_0\times 1}{2\pi d}$ out of the plane.

Thus force due to this magnetic field on wire B=$F_A=BiL$

$\frac{{\mu }_0\times 1}{2\pi d}\times i\times L$ towards wire A.

$F_C>F_A$

Thus net force is towards wire C.