30. Induction and Inductance

An outer solenoid with 30 turns is wound tightly around an inner coil 25cm long with a diameter of 4cm and 300 turns. The current in the inner solenoid is 0.12 A and is increasing at a rate of 1.75×10³A/s. a) What is the average magnetic flux through each turn of the outer coil? b) If the resistance of the outer coil is 20mΩ, what is the magnitude of the induced current through the outer coil?

(Note:for the multiple choice, select the correct answer for part (b) only.)

(II) Determine the mutual inductance per unit length between two long solenoids, one inside the other, whose radii are r₁ and r₂ (r₂ < r₁) and whose turns per unit length are n₁ and n₂.

Two coils have mutual inductance M = 3.25 × 10^-4 H. The current i1 in the first coil increases at a uniform rate of 830 A/s. (a) What is the magnitude of the induced emf in the second coil? Is it constant?

(II) A 2.44-m-long coil containing 265 loops is wound on an iron core (average μ = 1850μ₀) along with a second coil of 115 loops. The loops of each coil have a radius of 2.00 cm. (a) Determine the mutual inductance M. (b) If the current in the first coil drops uniformly from 12.0 A to zero in 98.0 ms, determine the emf induced in the second coil.