Question

Calculate the initial current in an inductor having inductance 4000 H, number of turns is 200 and the flux changes from 760 to 800 Wb. Current changes to 7A.

(a) 10A

(b) 2A

(c) 3A

(d) 5A

The question was asked in a job interview.

My enquiry is from Ferromagnetic Cored Inductor in a DC Circuit in portion Inductance in a DC Circuit of Basic Electrical Engineering

Answer 1

Correct answer is (d) 5A

For explanation: From the formula of incremental inductance, we know that:

L=(Change in flux/Change in current)*Number of turns

Substituting the values from the given question, we get change in current = 2A.

Change in current = final current- initial current.

2=7-initial current.

Initial current = 5A.