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 make an angle `theta` with each other.

Explanation

If `i` current flows in the larger coil, magnetic field produced at the centre will be perpendicular to the plane of larger coil. Now the area vector of smaller coil which is perpendicular to the plane of smaller coil will make an angle `theta` with the magnetic field.
Thus flux `vecB.vecA=(mu_(0)i)/(2a_(2)).pia_(1)^(2).cos theta`
or `M=(mu_(0)pia_(1)^(2)cos theta_(1))/(2a_(2))`