Two long parallel straight wires P and Q separated by a distance 5cm in air carry currents of 4A and 2A respectively in same direction. Find the magnitude of the force acting per cm of the wire P and indicate the direction of the force.

Explanation

Distance between the two wires, `r=5cm=(5)/(100)m` Force acting per metre,
`F=(mu_(0))/(4pi).(2I_(1)I_(2))/(r)=(4pixx10^(-7))/(4pi)xx(2xx4xx2)/((5)/(100))`
`=10^(-7)xx(16)/(5)xx100=3.2xx10^(-5)N.m^(-1)`
`:.` Force acting per cm `=(3.2xx10^(-5))xx(1)/(100)`
`=0.032dyn.cm^(-1)`
Since the wires are carrying currents in the same direction, so the force acting between the wires is attractive, Hence the force on each wire is directed towards the other wire and perpendicular to them.