Two straight wires are in parallel and carry electrical currents in opposite directions with the same magnitude of 2.0A. The distance between the two wires 5.0 m m. If one of the wires is infinitely long and the other the wire is 0.3 m long, what is the magnitude of the force between the two wires?

Two straight wires

Have current in opposite direction

i1=i2=i=2Amps

Distance between two wires

r=5mm=0.005m

Length of one wire is ∞

Length of second wire is 0.3m

Force between the wire,

The force between two parallel currents I1 and I2, separated by a distance r, has a magnitude per unit length given by

F/l = μoi1i2/2πr

F/l=μoi²/2πr

μo=4π*10^-7 H/m

The force is attractive if the currents are in the same direction, repulsive if they are in opposite directions.

F/l = μoi1i2/2πr

F/0.3=4π*10^-7*2²/2π•0.005

F/0.3=1.6*10^-4

Cross multiply

F=1.6*10^-4*0.3

F=4.8*10^-5N