Determine the mutual inductance of a doughnut coil and an infinite straight wire passing along its axis. The coil has recatangular cross-section, its inside radius is equal to `a` and the outside one, to `b`. The length of the doughtnut's cross-sectinla side parallel to the wire is equal to `h`. The coil has `N` turns. The system is located in a unifrom magnetic with permeability `mu`.

Explanation

Here, also, `B = (mu_(0) I)/(2pi r)` and `Phi = mu_(0) mu (I)/(2pi) int_(a)^(b) (h dr)/(r) N`
Thus, `L_(12) = (mu mu_(0) hN)/(2pi) In (b)/(a)`