MULTIPLE CHOICE QUESTIONS
Q.1 Under constant load conditions, the speed of a d.c. motor is affected by
(A) field flux
(B) armature current
(C) back e.m.f.
(D) both (b) and (c)
Q.2 It is possible to increase the field flux and, at the same time, increase the speed of a d.c. motor provided its .......... is held constant.
(A) applied voltage
(B) torque
(C) Armature circuit resistance
(D) armature current
Q.3 The current drawn by a 120 - V d.c. motor of armature resistance 0.5 Ω and back e.m.f. 110 V is .......... ampere.
(A) 20
(B) 240
(C) 220
(D) 5
Q.4 The shaft torque of a d.c. motor is less than its armature torque because of .......... losses.
(A) copper
(B) mechanical
(C) iron
(D) rotational
Q.5 A d.c. motor develops a torque of 200 N-m at 25 rps. At 20 rps it will develop a torque of
.......... N-m.
(A) 200
(B) 160
(C) 250
(D) 128
Q.6 Neglecting saturation, if current taken by a series motor is increased from 10 A to 12 A, the percentage increase in its torque is ........ percent
(A) 20
(B) 44
(C) 30.5
(D) 16.6
Q.7 If load on a d.c. shunt motor is increased, its speed is decreased due primarily to
(A) increase in its flux
(B) decrease in back e.m.f.
(C) increase in armature current
(D) increase in brush drop
Q.8 If the load current and flux of a d.c. motor are held constant and voltage applied across its
armature is increased by 10 per cent, its speed will
(A) decrease by about 10 per cent
(B) remain unchanged
(C) increase by about 10 per cent
(D) increase by 20 per cent.
Q.9 If the pole flux of a d.c. motor approaches zero, its speed will
(A) approach zero
(B) approach infinity
(C) no change due to corresponding change in back e.m.f.
(D) approach a stable value somewhere between zero and infinity.
Q.10 If the field circuit of a loaded shunt motor is suddenly opened
(A) it would race to almost infinite speed
(B) it would draw abnormally high armature current
(C) circuit breaker or fuse will open the circuit before too much damage is done to the motor
(D) torque developed by the motor would be reduced to zero.