Question

Two straight wires A and B of lengths 10 m and 12 m carrying currents of 4A and 6A respectively in opposite directions lie parallel to each other at a distance of 3cm. estimate the force on 15cm section of the wire B near its centre

Answer 1

We assume that the wires are long compared to distance between them and the 15cm section.

B at the 15 cm section  due to current in A: $\frac{Mu\ I}{2 π d}$
     $= \frac{Mu 4 }{2π 0.03 T}$

Field B is perpendicular to the length of wire B and to plane of A & B.

Force on the wire segment =
         = I L X B = 6A * 0.15 m * 21.22 Mu = 19.1 * Mu Newtons