15.
Two straight wires A and B of lengths 10m and 12m carrying currents of 4.0A and 6.0A respectively in opposite directions lie parallel to each other at a distance of 3.0cm. Estimate the force on a 15cm section of the wire B near its centre.
Suggested solution:
The ratio of the length of the wires to the separation between them is large (more than 300). Therefore, one can estimate the approximate force on a section of either of the two wires (near their centres) by using the exact result for force per unit length for two infinitely long wires carrying currents I1 and I2.
Force per unit length
Force on 15cm section of wire B (near it's centre)
= 1.6 x 10-4 x 0.15 N= 2.4 x 10-5 N
