# MCQ in AC Motors Part 2 | REE Board Exam

(Last Updated On: July 28, 2020) This is the Multiple Choice Questions Part 2 of the Series in AC Motors as one of the Electrical Engineering topic. In Preparation for the REE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electrical Engineering field, Electrical Engineering Books, Journals and other Electrical Engineering References.

#### Continue Practice Exam Test Questions Part 2 of the Series

Choose the letter of the best answer in each questions.

51.  EE Board Exam October 1990

Repeated starting and stopping of a motor is referred to as

A.  stepping

B.  jogging

C.  phasing

D.  none of these

Solution:

52.  EE Board Exam June 1990

An induction motor driven above synchronous speed is called

A.  induction regulator

B.  frequency changer

C.  induction generator

D.  phase converter

Solution:

Unsolved problems

53.  REE Board Exam September 2004

In an induction motor, what is the percent slip if the speed is 3,510?

A.  1

B.  1.5

C.  2

D.  2.5

54.  REE Board Exam September 2002

The speed of an induction motor is 1170 rpm. What is the frequency of the rotor current?

A.  2.5 Hz

B.  37.5 Hz

C.  1.5 Hz

D.  3.3 Hz

55.  REE Board Exam September 2002

A 3-phase, 220 volt induction motor having a power factor of 0.8 has 3% losses. Determine the current drawn by the motor.

A.  25.23 A

B.  43.69 A

C.  20.18 A

D.  14.56 A

56.  REE Board Exam April 2002

A three-phase squirrel cage motor is started by wye-delta starter. What shall be its starting torque relative to its rated voltage starting torque?

A.  33.3%

B.  42.3%

C.  57.7%

D.  100%

57.  ECE Board Exam November 1999

How do you call the speed of an alternating current (AC) induction motor?

A.  Varying supply frequency

B.  Varying series resistance of the field

C.  Varying supply voltage

D.  Varying both the supply voltage and frequency at the same time

Solution:

58.  ECE Board Exam November 1995

The best way to control the speed of an AC induction motor is by varying the _____.

A.  supply frequency

B.  both supply voltage and frequency simultaneously

C.  supply voltage

D.  series resistance of the field

Solution:

59.  ECE Board Exam November 1997

A two pole, three phase motor has _____ field poles.

A.  6

B.  8

C.  2

D.  4

Solution:

60.  ECE Board Exam November 2001

_____ refers to an AC generator.

A.  Commutator

B.  Motor (AC)

C.  Rotor

D.  Alternator

Solution:

61.  ECE Board Exam November 2000

Series motors operated on either AC or DC are sometimes called _____.

A.  Universal motors

B.  General motors

C.  Bavarian motors

D.  Anglo motors

Solution:

62.  ECE Board Exam April 2001

What does the term single-phase indicate?

A.  One input

B.  One current (one input)

C.  One time

D.  One voltage (one input)

Solution:

63.  ECE Board Exam November 1996

A.  Synchronous motor

B.  Squirrel cage motor

C.  Split phase motor

D.  Universal motor

Solution:

64.  ECE Board Exam November 1996

A two pole, one phase motor has _____ field poles.

A.  8

B.  2

C.  6

D.  4

Solution:

65.  What is the percent slip of a 4-pole induction motor if the output speed is 1,755 rpm?

A.  3

B.  5

C.  2.5

D.  4

Solution:

66.  Regarding skewing of motor bars in a squirrelcage induction motor, (SCIM) which statement is false.

A.  it prevents cogging

B.  it increases starting torque

C.  it produces more uniform torque

D.  it reduces motor ‘hum’ during its operation

Solution:

67.  The principle of operation of a 3-phase induction motor is most similar to that of a

A.  synchronous motor

B.  repulsion-start induction motor

C.  transformer with a shorted secondary

D.  capacitor-start, induction-run motor

Solution:

68.  The magnetizing current drawn by transformers and induction motors is the cause of their ____ power factor.

A.  zero

B.  unity

C.  lagging

Solution:

69.  The effect of increasing the length of air-gap in an induction motor will be to increase the

A.  power factor

B.  speed

C.  magnetizing current

D.  air-gap flux

Solution:

70.  In a 3-phase induction motor, the relative speed of stator flux with respect to ____ is zero.

A.  stator winding

B.  rotor

C.  rotor flux

D.  space

Solution:

71.  An eight pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 r.p.m. by a prime mover in the opposite direction of revolving magnetic field. The frequency of rotor current is

A.  60 Hz

B.  120 Hz

C.  180 Hz

D.  none of these

Solution:

72.  A 3-phase 4 pole, 50 Hz induction motor runs at a speed of 1440 r.p.m. The rotating field produced by the rotor rotates at a speed of _____ r.p.m. with respect to the rotor.

A.  1500

B.  1440

C.  60

D.  0

Solution:

73.  In a 3- induction motor, the rotor field rotates at synchronous speed with respect to

A.  stator

B.  rotor

C.  stator flux

D.  none of these

Solution:

74.  Irrespective of the supply frequency, the torque developed by a SCIM is the same whenever ____ is the same.

A.  supply voltage

C.  rotor resistance

D.  slip speed

Solution:

75.  The number of stator poles produced in the rotating magnetic field of a 3-Ф induction motor having 3 slots per pole per phase is

A.  3

B.  6

C.  2

D.  12

Solution:

76.  The power factor of a squirrel-cage induction motor is

A.  low at light loads only

B.  low at heavy loads only

C.  low at light and heavy loads only

D.  low at rated load only

Solution:

77.  Which of the following rotor quantity in a SCIM does NOT depend on its slip?

A.  reactance

B.  speed

C.  induced emf

D.  frequency

Solution:

78.  A 6-pole, 50-Hz, 3- induction motor is running at 950 rpm and has rotor Cu loss of 5 kW. Its rotor input is ____ kW.

A.  100

B.  10

C.  95

D.  5.3

Solution:

79.  The efficiency of a 3-phase induction motor is approximately proportional to

A.  (1 – s)

B.  s

C.  N

D.  Ns

Solution:

80.  A 6-pole, 50-Hz, 3- induction has a full-load speed of 950 rpm. At half load, its speed would be ____ rpm.

A.  475

B.  500

C.  975

D.  1000

Solution:

81.  If rotor input of a SCIM running with a slip of 10% is 100 kW, gross power developed by its rotor is ____ kW.

A.  10

B.  90

C.  99

D.  80

Solution:

82.  Pull-out torque of a SCIM occurs at that value of slip where rotor power factor equals

A.  unity

B.  0.707

C.  0.866

D.  0.5

Solution:

83.  When applied rated voltage per phase is reduced by one-half, the starting torque of a SCIM becomes ____ of the starting torque with full voltage.

A.  ½

B.  ¼

C. 1/8

D. ¾

Solution:

84.  If maximum torque of an induction motor is 200 kg-m at a slip of 12%, the torque at 6% slip would be ____ kg-m.

A.  100

B.  160

C.  50

D.  40

Solution:

85.  The fractional slip of an induction motor is the ratio

A.  rotor Cu loss/rotor input

B.  stator Cu loss/stator input

C.  rotor Cu loss/rotor output

D.  rotor Cu loss/stator Cu loss

Solution:

86.  The torque developed by a 3-phase induction motor depends on the following three factors:

A.  speed, frequency, number of poles

B.  voltage, current and stator impedance

C.  synchronous speed, rotor speed and frequency

D.  rotor emf, rotor current and rotor p.f.

Solution:

87.  If the stator voltage and frequency of an induction motor are reduced proportionately, its

A.  locked rotor current is reduced

B.  torque developed is increased

C.  magnetizing current is decreased

D.  both A and B

Solution:

88.  The efficiency and p.f. of a SCIM increases in proportion to its

A.  speed

C.  voltage

D.  rotor torque

Solution:

89.  A SCIM runs at constant speed only so long as

A.  torque developed by it remains constant

B.  its supply voltage remains constant

C.  its torque exactly equals the mechanical load

D.  stator flux remains constant

Solution:

90.  The synchronous sped of a linear induction motor does NOT depend on

A.  width of pole pitch

B.  number of poles

C.  supply frequency

D.  any of these

Solution:

91.  Thrust developed by a linear induction motor depends on

A.  synchronous speed

B.  rotor input

C.  number of poles

D.  both A and B

Solution:

92.  The stator of a 3-phase induction motor produces ____ magnetic field.

B.  rotating

C.  alternating

D.  none of these

Solution:

93.  An induction motor is preferred to a dc motor because it

A.  provides high starting torque

B.  provides fine speed control

C.  has simple and rugged construction

D.  none of these

Solution:

94.  A 3-phase induction motor is

A.  essentially a constant speed motor

B.  a variable speed motor

C.  very costly

D.  not easily maintainable

Solution:

95.  The air gap between stator and rotor of a 3-phase induction motor ranges from

A.  2 cm to 4 cm

B.  0.4 mm to 4 mm

C.  1 cm to 2 cm

D.  4 cm to 6 cm

Solution:

96.  If the frequency of 3-phase supply to the stator of a 3-phase induction motor is increased, the synchronous speed

A.  is decreased

B.  is increased

C.  remains unchanged

D.  none of these

Solution:

97.  If Ns is the speed of rotating flux and Nr the speed of the rotor, then the rate at which the flux cuts the rotor conductors is directly proportional to

A.  N

B.  N

C.  Ns – Nr

D.  Nr – Ns

Solution:

98.  In a 3-phase induction motor, the rotor speed is ____ the synchronous speed.

A.  greater than

B.  smaller than

C.  equal to

D.  none of these

Solution:

99.  The synchronous speed of a 3-phase induction motor having 20 poles and connected to a 50 Hz source is

A.  600 rpm

B.  1000 rpm

C.  1200 rpm

D.  300 rpm

Solution:

100.  The relation among synchronous speed (Ns), rotor speed (Nr) and slip (s) is

A.  Nr = (s – 1)Ns

B.  Nr = (1 – s)Ns

C.  Nr = (1 + s)Ns

D.  Nr = sNs

Solution:

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