Deck 3: Electric Motors and Their Characteristics

Question 1

Which of the following single-phase motors has relatively poor starting torque ?

A)Universal motor
B)Repulsion motor
C)Capacitor motor
D)All single phase motors have zero starting torque

Answer 1

Capacitor motor

Question 2

Which type of load is offered by cranes and hoists ?

A)Gradually varying load
B)Non-reversing, no-load start
C)Reversing, light start
D)Reversing, heavy start

Answer 2

Reversing, heavy start

Question 3

The speed of a universal motor is generally reduced by using

A)gear trains
B)V-belts
C)brakes
D)chains

Answer 3

gear trains

Question 4

Which of the following motors can be used for unity power factor ?

A)Capacitor run motor
B)Shaded pole motor
C)Hysteresis motor
D)Schrage motor

Question 5

When a D.C. series motor is connected to A.C. supply, the power factor will be low because of

A)high inductance of field and armature circuits
B)induced current in rotor due to variations of flux
C)fine copper wire winding
D)none of the above

Question 6

The direction of rotation of universal motor can be reversed the by reversing the flow of current through

A)armature winding
B)field winding
C)either armature winding or field winding
D)none of the above

Question 7

In which single-phase motor, the rotor has no teeth or winding ?

A)Split phase motor
B)Reluctance motor
C)Hysteresis motor
D)Universal motor

Question 8

Which motor is normally free from mechanical and magnetic vibrations ?

A)Split phase motor
B)Universal motor
C)Hysteresis motor
D)Shaded pole motor

Question 9

As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for

A)fans
B)blowers
C)sound equipment
D)mixer grinders

Question 10

A reluctance motor

A)is self-starting
B)is constant speed motor
C)needs no D.C. excitation
D)all of the above

Question 11

In a hysteresis motor, the rotor must have

A)retentivity
B)resistivity
C)susceptibility
D)none of the above

Question 12

The rotor of a hysteresis motor is made of

A)aluminium
B)cast iron
C)chrome steel
D)copper

Question 13

The electric motor used in portable drills is

A)capacitor run motor
B)hysteresis motor
C)universal motor
D)repulsion motor

Question 14

Which of the following applications always have some load whenever switched on ?

A)Vacuum cleaners
B)Fan motors
C)Pistol drills
D)All of the above

Question 15

The speed control of universal motor used for sewing machines is by

A)friction
B)varying the resistance
C)tapping the field
D)centrifugal mechanism

Question 16

Torque developed by a single phase induction motor at starting is

A)pulsating
B)uniform
C)none of the above
D)nil

Question 17

In split phase motor main winding is of

A)thin wire placed at the top of the slots
B)thin wire placed at the bottom of the slots
C)thick wire placed at the bottom of the slots
D)thick wire placed at the top of the" slots

Question 18

In repulsion motor, maximum torque is developed when

A)brush axis is at 45° electrical to the field axis
B)brush axis coincides with the field axis
C)brush axis is at 90° electrical to the field axis
D)none of the above

Question 19

If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in

A)damage to the starting winding
B)damage to the centrifugal switch
C)overloading of running winding
D)none of the above

Question 20

Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.

A)shunt motor
B)series motor
C)compound motor
D)separately excited motor

Question 21

In a ceilingfan employing capacitor run motor

A)secondary winding surrounds the primary winding
B)primary winding surrounds the secondary winding
C)both are usual arrangements
D)none of the above

Question 22

The shaded pole motor is used for

A)high starting torque
B)low starting torque
C)medium starting torque
D)very high starting torque

Question 23

The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it

A)improves the efficiency
B)helps the rotor teeth to remain under the stator teeth
C)helps in reducing the tendency of the rotor teeth to remain under the stator teeth
D)improves the power factor

Question 24

The speed/load characteristics of a universal motor is same as that of

A)A.C. motor
B)D.C. shunt motor
C)D.C. series motor
D)none of the above

Question 25

The purpose of stator winding in the compensated repulsion motor is to

A)provide mechanical balance
B)improve power factor and provide better speed regulation
C)prevent hunting in the motor
D)eliminate armature reaction