Single Phase Induction Motor MCQ

81. In hand tool applications, which one of the following single-phase motors is used?

(a) Shaded pole motor.
(b) Capacitor start motor.
(c) Capacitor run motor.
(d) AC series motor.

82. A dc shunt motor does not operate on ac due to

(a) low resistance of armature circuit.
(b) high resistance of field circuit.
(c) high inductance of field circuit.
(d) reversal of polarity. [A.M.I.E- Sec B. E. Machines Winter 1994]

83. A dc series motor is accidently connected to single phase ac supply. The torque produced will be

(a) of zero average value.
(b) oscillating.
(c) steady and unidirectional.
(d) pulsating and unidirectional. [U.P.S.C. I.E.S. 2002]

84. A 230 V dc series motor is connected to a 230 V ac supply

(a) the motor will vibrate violently.
(b) the motor will run with less efficiency and more sparking.
(c) the motor will not run.
(d) the fuse will be blown. [U.P.S.C. I.E.S. 1998]

85. If a dc series motor is operated on ac supply, it

(a) will not start at all.
(b) will start and run but will have poor performance such as excessive sparking, poor efficiency and poor power factor.
(c) will get damaged due to burning of its windings.
(d) will run at excessively high speed.

86. The operation of an ordinary dc series motor when operated on ac, would not be satisfactory. The reason(s) is/are

(a) excessive eddy-current losses in the field core and yoke due to alternation in field flux.
(b) heavy sparking due to induced voltages and currents in the armature coils short-circuited by the brushes while undergoing commutation.
(c) abnormal voltage drop and low power factor due to inductance of the field winding.
(d) non-uniform torque due to reversal of field and armature currents every half cycle.
(e) all of the above.

87. AC series motors are built with as few field turns as possible to reduce

(a) flux.
(b) eddy current losses.
(c) reactance.
(d) speed.

88. AC series motors in comparison to dc series motors do not have

(a) lesser number of field turns.
(b) larger number of armature conductors.
(c) larger number of poles with lesser flux per pole.
(d) wider air gap.
(e) brushes of smaller width.

89. AC series motors in comparison to dc series motors do not have

(a) all parts of magnetic circuits laminated.
(b) multi-turn armature coils.
(c) very short air gap.
(d) single turn armature coils.

90. In a large sized ac series motor, the inductive effects of armature and field cause

(a) serious commutation difficulties.
(b) heavy iron losses.
(c) low power factor.
(d) all of the above.

91. Which of the following statements associated with an ac series

(a) Its speed falls with the increase in load torque.
(b) Its power factor deceases with the increase in load torque.
(c) Its torque-speed characteristic is similar to that of a dc shunt motor.
(d) Its torque-speed characteristic is similar to that of a dc series motor.

92. In an ac series motor

(a) the starting current is about 2.5 times of full load current.
(b) the starting torque is about 4 times of full load torque.
(c) power factor varies from 0.9 to 0.95 lagging.
(d) all of the above.

93. In an ac series motor, compensation winding is provided to

(a) neutralize the armature mmf.
(b) improve commutation and reduce sparking at the brushes.
(c) reduce reactance drop.
(d) reduce armature heating and vibrations.
(e) all of the above except (d).

94. AC series motors are preferably operated on low voltage and low frequency because

(a) low operating voltage reduces the inductance.
(b) lower operating frequency reduces reactance and iron loss and improves commutation.
(c) both (a) and (b).
(d) none of these.

95. In an ac series motor, power factor is improved by

(a) increasing the inductance of armature and field windings.
(b) reducing the inductance of armature and field windings.
(c) increasing the supply voltage.
(d) both (a) and (c).

96. In an ac series motor, commutation is improved by

(a) reducing the number of armature conductors.
(b) providing commutating poles.
(c) providing commutating poles and shunting winding of each of these poles with a non-inductive resistance .
(d) increasing field winding turns.

97. In ac series motors armature coils are usually connected to commutator

(a) through resistors.
(b) through inductors.
(c) through capacitors.
(d) solidly.

98. For improvement of commutation in ac series motors shunted commutating poles are commonly used and commutating pole windings are shunted by a

(a) non-inductive resistor to make the commutating pole current to lead the main current.
(b) non-inductive resistor to make the commutating pole current to lag behind the main current.
(c) reactor to make the commutating pole current to lag behind the main current.
(d) given statements are false.

99. A universal motor is one which has

(a) constant speed.
(b) constant output.
(c) capability of operating both on ac and dc with comparable performance.
(d) maximum efficiency.

100. Which of the following statements associated with universal motor is incorrect ?

(a) It is a series connected commutator motor.
(b) It is a constant speed motor.
(c) Its armature is of same construction as ordinary series motor.
(d) Like all series motors, its no-load speed is very high.
(e) It is usually built into the device it drives.