Question

FIGURE 1 shows two long parallel wires 2 cm apart. Wire P carries a current 7 A to

the right. Point C is 3 cm from wire Q and in the same plane as wire P and Q.

Determine the magnitude and direction of current in wire Q so that the magnetic field

at C is zero.

Answer 1

$F=\frac{\mu_0I_1I_2}{2\pi d}-\frac{\mu_0I_1I_2}{2\pi (d+r)}=0,$

$I_2=3.7~A.$