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 magnetomotive force.

(a) 1442At

(b) 1342At

(c) 1432At

(d) 1344At

I have been asked this question in unit test.

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

Answer 1

Right answer is (d) 1344At

To explain: 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.