Question

Two long parallel straight wires P and Q, seperated by a distance of 10cm in air, carry current of 2A and 5A, respectively, in opposite directions. Then the force, on 20cm length of wire Q, is

(1) 2 x 10^-7 N, perpendicular to the length of Q and acts towards P

(2) 2 x 10^-6 N, perpendicular to the length of Q and acts away from P

(3) 2 x 10^-6 N, and acts towards P

(4) 2 x 10^-7 N, and acts away from P

Answer 1

(2) 2 x 10^-6 N, perpendicular to the length of Q and acts away from P

The direction of F will be perpendicular to the length Q and it acts away from P. (F between ‘unlike currents’, is a force of repulsion)