Question

Average coil emf for 20 coil turns (E1) and 40 coil turns (E2), will have ratio E1/E2=____ (assuming all other parameters same for both machines).

(a) 1/2

(b) 2/1

(c) 1/4

(d) 4/1

I had been asked this question in a national level competition.

My enquiry is from EMF and Torque Production in chapter Circuit Model, Emf and Torque of DC Machines

Answer 1

Right option is (a) 1/2

The best explanation: Emf generated in a DC machine is directly proportional to number of coil turns, Flux per pole, number of poles and armature speed in rad/s. Thus, ratio E1/E2= 20/40 (assuming all other parameters same for both machines).