Question

For an inductor made from magnetic core, with two air gaps of equal length g, exciting coil with 1000 turns, A=5cm∗5cm and g=1cm, what will be the coil inductance?

(a) 0.314H

(b) 0.157H

(c) 0.078H

(d) 0.628H

The question was posed to me during an internship interview.

I want to ask this question from Torque Production and Dynamic Equations in section Basic Concepts in Rotating Machines of Electrical Machines

Answer 1

Right choice is (b) 0.157H

Easy explanation: Reluctance Rl=2g/μ0A and coil Inductance L=N^2/Rl = N^2μ0A/2g = (1000)^2(4π∗10^-7)(0.05)^2/(2∗0.01) = 0.15708H.