1. The generator characteristic shown in Figure 9.28 is for a
(a) shunt machine
(b) series machine
(c) differentially compounded machine
(d) cumulatively compounded machine
2.The speed of a DC motor can be increased by
(a) reducing the brush pressure
(b) weakening the field strength
(c) strengthening the field
(d) reducing the armature voltage
3.The direction of rotation of a DC shunt motor can be reversed by
(a) reversing the polarity of the DC supply
(b) reversing the connections of both the armature and the field
(c) changing to a series field
(d) reversing either the armature or the field connections
4. Show by a series of MMF vector diagrams how a ‘rotating’ field is produced by
a spaced three-phase winding such as in an induction motor.
5.Calculate the synchronous speed of a 10-pole three-phase machine connected to
a 50 Hz supply.
6.If the synchronous speed of a three-phase machine connected to a 50 Hz supply
is 750 r/min, how many poles has it?
7. What frequency is applied to a four-pole three-phase stator with a synchronous
speed of 1800 r/min?