Question

Electromagnetic force and/or torque developed in any physical system, acts in such a direction as to tend to ____________

(a) increase both the field energy and co-energy at constant current

(b) increase the field energy and decrease the co-energy at constant current

(c) decrease both the field energy and co-energy at constant current

(d) decrease the field energy and increase the co-energy at constant current

This question was addressed to me in quiz.

The question is from Singly Excited Magnetic Systems topic in portion Magnetic Circuits of Electrical Machines

Answer 1

Correct choice is (a) increase both the field energy and co-energy at constant current

To elaborate: fe = (∂Wfld^1(i,x))/∂x = (∂Wfld(i,x))/∂x.