Question

What is the relation between force and the air gap length in the flat-faced armature type?

(a) force is directly proportional to the air gap length

(b) force is indirectly proportional to the air gap length

(c) force is directly proportional to the square of the air gap length

(d) force is indirectly proportional to the square of the air gap length

The question was asked in an international level competition.

I'm obligated to ask this question of Types of Electromagnets in division Design of Electromagnets of Design of Electrical Machines

Answer 1

Right choice is (c) force is directly proportional to the square of the air gap length

Easy explanation: The force is directly proportional to the square of the air gap length. This condition exists under ideal conditions wherein the effects of saturation and magnetic leakage are negligible.