Page 664 - Basic Electrical Engineering

machine having 1500 armature conductors is

a. 4
b. 2
c. 6
d. 8.

10. Which of the following statements is not true for the EMF induced in a dc machine?

a. EMF induced is directly proportional to speed of the armature
b. EMF induced is inversely proportional to flux per pole
c. EMF induced is directly proportional to number of armature conductors
d. EMF is directly proportional to the flux per pole.

11. The direction of rotation of a dc motor can be changed

a. by reversing the polarities of the supply
b. by reversing either the polarities of the supply to armature or to the poles
c. by reversing only the polarities of the supply to the armature
d. by reversing only the polarities of the supply to the field poles.

12. The speed of a dc motor is

a. directly proportional to back EMF and inversely proportional to flux
b. inversely proportional to back EMF and directly proportional to flux
c. directly proportional to both back EMF and flux
d. inversely proportional to both back EMF and flux.

13. The nature of EMF induced in the armature coils in a dc machine is

a. dc
b. ac
c. pulsating dc
d. variable dc.

14. A dc machine is connected to 220 V supply mains. Its armature resistance is 0.2 Ω. What
should the magnitude of EMF generated so that it may feed 100 A to the supply?

a. 200 V
b. 220 V
c. 240 V
d. 260 V.

15. Residual magnetizm of the field poles is necessary for the voltage built up in

a. dc shunt motor
b. dc shunt generator
c. dc series motor