Find the mutual inductance of two concentric coils of radii `a_(1)` and `a_(2)(a_(1) lt lt a_(2))` if the planes of the coils are same.

Explanation

Let a current `i` flow in coil of radius `a_(2)`
Magnetic field at the centre of coil `=(mu_(0)i)/(2a_(2))pia_(1)^(2)`
or `Mi=(mu_(0)i)/(2a_(2))pia_(1)^(2)` or `M=(mu_(0)pia_(1)^(2))/(2a_(2))`