Case : Read the passage and answer the question(s).

Consider two long co-axial solenoids each of length l. We denote the radius of the inner solenoid S1 by r1 and the number of turns per unit length by n1. The corresponding quantities for the outer solenoid S2 are r2 and n2, respectively. Let N1 and N2 be the total number of turns of coils S1 and S2, respectively.

What will the mutual inductance of S2 w.r.t. S1 be given by?

μπr²1 n1 n2 l

Expression for mutual inductance.