Q.

Two long straight wires P and Q carrying equal current 10 A each were kept parallel to each other at 5 cm distance. Magnitude of magnetic force experienced by 10 cm length of wire P is F1. If the distance between the wires is halved and the currents on them are doubled, the force F2 on 10 cm length of wire P will be          [2023]

1 10F1  
2 8F1  
3 F18  
4 F110  

Ans.

(2)

Force per unit length between two parallel straight wires

=μ0i1i22πd

F1F2=μ0(10)22π(5)μ0(20)22π(52)=18  F2=8F1