Question

The speed of a DC shunt motor can be increased by ______

(a) Increasing the resistance in armature circuit

(b) Increasing the resistance in field circuit

(c) Reducing the resistance in the field circuit

(d) Reducing the resistance in the armature circuit

The question was asked by my college director while I was bunking the class.

Enquiry is from Speed Control Using Field Control of Shunt Motor topic in section DC Motors of DC Machines

Answer 1

Correct answer is (b) Increasing the resistance in field circuit

The explanation is: Speed of the DC motor is directly proportional to the back emf and inversely proportional to the flux produced by field. Where, flux produced is directly proportional to the current passing through the field winding (linear magnetization).