Two parallel wires separated by a distance of 10cm carry currents of 10 A and 40 A along the same direction, Where should a third current be placed so that it experience no magnetic force?

Explanation

Let the third wire placed x cm from 10 A current wire. According to question.`(mu_oi )/(2pix) = (mu_o40)/(2pi(10 - x)`
`rArr 10 -x = 4x`
`rArr x = 2 cm`
Hence it is 2 cm from the 10 A current wire.