Question

A ring having a cross-sectional area of 500 mm^2, a circumference of 400 mm and ϕ=800microWb has a coil of 200 turns wound around it. Relative permeability of ring is 380. Calculate the magnetising current.

(a) 6.7A

(b) 7.7A

(c) 7.6

(d) 6.1A

The question was asked in a job interview.

This key question is from Ohm’s Law for a Magnetic Circuit topic in section Simple Magnetic Circuits of Basic Electrical Engineering

Answer 1

Right choice is (a) 6.7A

For explanation: Reluctance = l/(µ*A) = l/(µrµ0*A)

Substituting the values, we get Reluctance S=1.68*106 A/Wb.

F=ϕS     Substituting the given values, we get F = 1344At.

I=F/N    Substituting the values from the question, we get I=6.7A.