# Solved Problems-11

Problem-11
Determine the force between two parallel circular coaxial coils of radius â€˜Râ€™ which are a small distance â€˜dâ€™ apart in free space and carry currents I1 and I2. Assume that each of the coils has a single turn.
Solution
As the distance between the coils is very small compared to the radius of the coils, the two coils can be treated as parallel current-carrying wires. The force on one of the coils (say C1) per unit length due to the other coil (say C2) can be written as,

Therefore, the net force is given as,
Parallel coaxial circular coils