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.

Mutual inductance between two magnetically coupled coils depends on which of the following?

All the above

Expression for mutual inductance.

M = μ n₁ n₂ A l