A toroidal solenoid with mean radius r and cross-sectional area A is wound uniformly with N1 turns. A second toroidal solenoid with N2 turns is wound uniformly on top of the first, so that the two solenoids have the same cross-sectional area and mean radius.
What is the mutual inductance of the two solenoids? Assume that the magnetic field of the first solenoid is uniform across the cross section of the two solenoids.
Express your answer in terms of the variables N1, N2, A, r, magnetic constant μ0 and others appropriate constants.
The Attempt at a Solution
M = μ0⋅N1⋅N2⋅A this is what I have so far and I know that I need to include the r in the equation somewhere but not really sure where or why. Could somebody please explain. Thank you.