- As hysteresis motors are free from mechanical and magnetic vibrations, therefore, these are considered as suitable for
A) Sound equipment
B) Blowers
C) Mixer grinders
D) Fans
Explanation: Hysteresis motors are known for their quiet operation and lack of vibrations, making them ideal for sound equipment like record players and tape recorders.
The value of starting capacitor of a fractional horse-power motor will be
A) 400 μF
B) 100 μF
C) 200 μF
D) 300 μF
Explanation: Fractional horsepower motors typically use a starting capacitor in the range of 100 μF to provide the necessary phase shift for starting.
Which of the following motors is used for the unity power factor?
A) Universal motor
B) Hysteresis motor
C) Schrage motor
D) Reluctance motor
Explanation: The Schrage motor is designed to operate at a unity power factor, making it efficient for certain applications.
The speed control of universal motor used for sewing machines is by
A) Tapping the field
B) Friction
C) Centrifugal mechanism
D) Varying the resistance
Explanation: Speed control in universal motors used in sewing machines is often achieved by varying the resistance in the circuit.
Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.
A) Series motor
B) Compound motor
C) Shunt motor
D) Separately excited motor
Explanation: The speed-torque characteristic of a repulsion induction motor is similar to that of a DC compound motor, offering good starting torque and speed regulation.
The purpose of the stator winding in the compensated repulsion motor is to
A) Prevent hunting in the motor
B) Improve power factor and provide better speed regulation
C) Eliminate armature reaction
D) Provide mechanical balance
Explanation: The stator winding in a compensated repulsion motor helps improve the power factor and provides better speed regulation.
When a D.C. series motor is connected to A.C. supply, the power factor will be low because of
A) Induced current in rotor due to variations of flux
B) None of these answers
C) High inductance of field and armature circuits
D) Fine copper wire winding
Explanation: When a DC series motor is connected to an AC supply, the high inductance of the field and armature circuits results in a low power factor.
Which of the following statements regarding reluctance-start motor is incorrect?
A) It is similar to reluctance motor
B) So far as its basic working principle is concerned, it is similar to shaded pole motor
C) The air-gap between rotor and salient poles is non-uniform
D) It is basically an induction motor and not a synchronous one
Explanation: The reluctance-start motor is a type of synchronous motor, not an induction motor.
What could be the size of a universal motor for use in vacuum cleaners?
A) 3/4 H.P.
B) 1/4 H.P.
C) 2 H.P.
D) 1 H.P.
Explanation: Universal motors used in vacuum cleaners are typically small, around 1/4 H.P., due to their high-speed operation.
The centrifugal switch is used to disconnect starting winding when the motor has
A) Picked up about 10 to 25 per cent of rated speed
B) Run for about 5 minutes
C) Run for about 1 minute
D) Picked up about 50 to 70 per cent of rated speed
Explanation: The centrifugal switch disconnects the starting winding once the motor reaches 50-70% of its rated speed.
Which of the following motor will have a relatively higher power factor?
A) Capacitor run motor
B) Capacitor start motor
C) Split phase motor
D) Shaded pole motor
Explanation: Capacitor run motors have a higher power factor compared to other single-phase motors due to the continuous operation of the capacitor.
The range of efficiency for shaded pole motors is
A) 50% to 75%
B) 5% to 35%
C) 80% to 90%
D) 95% to 99%
Explanation: Shaded pole motors are less efficient, typically ranging from 5% to 35%.
For ceiling fans generally the single-phase motor used is
A) Split-phase type
B) Permanent capacitor type
C) Capacitor start and run type
D) Capacitor-start type
Explanation: Ceiling fans commonly use permanent capacitor motors for better efficiency and smooth operation.
If starting winding of a single-phase induction motor is left in the circuit, it will
A) Run slower
B) Run faster
C) Draw excessive current and overheat
D) Spark at light loads
Explanation: Leaving the starting winding in the circuit causes excessive current flow, leading to overheating.
A reluctance motor
A) All of these answers
B) Is constant speed motor
C) Is self-starting
D) Needs no D.C. excitation
Explanation: Reluctance motors do not require DC excitation and operate based on the principle of magnetic reluctance.
In a hysteresis motor, the rotor must have
A) Resistivity
B) Susceptibility
C) None of these answers
D) Retentivity
Explanation: The rotor in a hysteresis motor must have high retentivity to maintain magnetization and produce torque.
Which motor will make the least noise?
A) Universal motor
B) Capacitor motor
C) Shaded-pole motor
D) Hysteresis motor
Explanation: Hysteresis motors are known for their quiet operation due to the absence of mechanical vibrations.
Shading coils, in case of a shaded pole motor, are used to
A) Reduce friction losses
B) Protect against sparking
C) Reduce windage losses
D) Produce rotating magnetic field
Explanation: Shading coils create a phase shift in the magnetic field, producing a rotating magnetic field to start the motor.
If a D.C. series motor is operated on an A.C. supply, it will
A) All of these answers
B) Spark excessively
C) Have poor efficiency
D) Have poor power factor
Explanation: Operating a DC series motor on AC supply causes excessive sparking due to the alternating current.
In repulsion motor, maximum torque is developed when
A) None of these answers
B) Brush axis is at 90° electrical to the field axis
C) Brush axis is at 45° electrical to the field axis
D) Brush axis coincides with the field axis
Explanation: Maximum torque is developed when the brush axis is at 90° electrical to the field axis.
In A.C. series motor compensating winding is employed to
A) None of these answers
B) Reduce sparking at the brushes
C) Reduce the effects of armature reaction
D) Increase the torque
Explanation: The compensating winding reduces the effects of armature reaction, improving motor performance.
A.C. series motor as compared to D.C. series motor has
A) Smaller brush width
B) All of these answers
C) Less air gap
D) Less-number of field turns
E) More number of armature turns
Explanation: AC series motors have smaller brush width, less air gap, fewer field turns, and more armature turns compared to DC series motors.
In a shaded pole motor, the shading coil usually consist of
A) A single turn of heavy wire which is in parallel with running winding
B) None of these answers
C) A single turn of heavy copper wire which is short-circuited and carries only induced current
D) A multilayer fine gauge copper wire in parallel with running winding
Explanation: The shading coil is a single turn of heavy copper wire that is short-circuited and carries induced current.
Centrifugal switch disconnects the auxiliary winding of the motor at about ____percent of synchronous speed
A) 30 to 40
B) 80 to 90
C) 70 to 80
D) 100
Explanation: The centrifugal switch disconnects the auxiliary winding at 70-80% of synchronous speed.
Reluctance motors are
A) Singly excited
B) Doubly excited
C) None of these answers
D) Either doubly excited or singly excited
Explanation: Reluctance motors are singly excited, meaning they require only one power source.
A schrage motor can run on
A) All of these answers
B) Positive slip
C) Zero slip
D) Negative slip
Explanation: A Schrage motor can operate at positive, zero, or negative slip, making it versatile.
Short-circuiter is used in
A) None of these answers
B) Repulsion motor
C) Repulsion start induction run motor
D) Repulsion induction motor
Explanation: The short-circuiter is used in repulsion start induction run motors to transition from repulsion to induction operation.
Which of the following motors would you select for vacuum cleaners?
A) Hysteresis motor
B) Repulsion motor
C) Universal motor
D) Reluctance motor
Explanation: Universal motors are commonly used in vacuum cleaners due to their high-speed operation.
In a split-phase motor the ratio of the number of turns for starting winding to that for running winding is
A) More than one
B) Less than one
C) Two
D) One
Explanation: The starting winding has fewer turns compared to the running winding, so the ratio is less than one.
A repulsion-start induction-run single phase motor runs as an induction motor only when
A) Short-circuiter is disconnected
B) Stator winding is reversed
C) Brushes are shifted to the neutral plane
D) Commutator segments are short-circuited
Explanation: The motor operates as an induction motor when the commutator segments are short-circuited.
A universal motor is one which
A) Runs at dangerously high speed on no-load
B) Can be marketed internationally
C) Any of these answers
D) Can be operated either on D.C. or A.C. supply at approximately the same speed and output
Explanation: A universal motor can run on both AC and DC supplies with similar performance.
A shaded pole motor does not possess
A) Commutator
B) All of these answers
C) Capacitor
D) Centrifugal switch
Explanation: Shaded pole motors do not have a commutator, capacitor, or centrifugal switch.
The electric motor used in portable drills is
A) Capacitor run motor
B) Repulsion motor
C) Hysteresis motor
D) Universal motor
Explanation: Universal motors are used in portable drills due to their high-speed operation and compact size.
If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then
A) Current drawn by the motor will be excessively high
B) Motor will not come up to speed
C) Electrolytic capacitor will, in all probability, suffer breakdown
D) Motor will not carry the load
Explanation: If the centrifugal switch fails to open, the electrolytic capacitor may overheat and break down.
If a particular application needs high speed and high starting torque, then which of the following motor will be preferred?
A) Universal motor
B) Shaded pole type motor
C) Capacitor start motor
D) Capacitor start and run motor
Explanation: Universal motors provide high speed and high starting torque, making them suitable for such applications.
If a single-phase motor runs hot the probable cause cannot be
A) High voltage
B) Shorted stator coils
C) Low voltage
D) Blown fuses
Explanation: Blown fuses would cause the motor to stop, not overheat.
Electrical faults in a motor occur most commonly in its
A) Control equipment
B) Commutator
C) Motor winding
D) Brushes
Explanation: Motor windings are the most common location for electrical faults due to insulation breakdown or overheating.
A universal motor operates on
A) Approximately constant speed and load
B) Constant load and varying speed
C) Constant speed and varying load
D) Synchronous speed with varying load
Explanation: Universal motors operate at varying speeds under constant load conditions.
Which of the following applications would need the smallest size of motor?
A) Sewing machine
B) Table fan
C) Electric clock
D) Domestic mixi
Explanation: Electric clocks require very small motors due to their low power requirements.
Which of the following statements regarding permanent-split single value capacitor motor is incorrect?
A) It is easily reversed because of its low running torque
B) It is more sensitive to voltage variations because of its low running torque
C) It is generally used for exhaust and intake fans and unit-heaters
D) It has very low power factor at full load
Explanation: Permanent-split capacitor motors typically have a good power factor at full load.
Which motor is relatively free from mechanical and magnetic vibrations?
A) Reluctance motor
B) Shaded-pole motor
C) Universal motor
D) Hysteresis motor
Explanation: Hysteresis motors are known for their smooth operation and lack of vibrations.
A single-phase induction motor is
A) Inherently self-starting with low torque
B) Inherently non-self-starting with low torque
C) Inherently self-starting with high torque
D) Inherently non-self-starting with high torque
Explanation: Single-phase induction motors are not self-starting and require auxiliary means to start.
If the centrifugal switch does not open at 70 to 80 percent of the synchronous speed of the motor, it would result in
A) Overloading of running winding
B) Damage to the starting winding
C) Damage to the centrifugal switch
D) None of the above
Explanation: If the centrifugal switch fails to open, the starting winding may overheat and get damaged.
For which of the applications a reluctance motor is preferred?
A) Signaling and timing devices
B) Lifts and hoists
C) Refrigerators
D) Electric shavers
Explanation: Reluctance motors are used in signaling and timing devices due to their precise speed control.
Direction of rotation of a split-phase motor can be reversed by reversing the connection of
A) Both running winding only and starting winding only
B) Starting winding only
C) Running winding only
D) Either running winding only or starting winding only
Explanation: Reversing either the running or starting winding will reverse the motor's direction.
In a capacitor start single-phase motor when the capacitor is replaced by a resistance
A) Torque will increase
B) Motor will continue to run in same direction
C) Motor will run in reverse direction
D) The motor will consume less power
Explanation: Replacing the capacitor with a resistance can cause the motor to run in the reverse direction.
In split-phase motor main winding is of
A) Thick wire placed at the bottom of the slots
B) Thick wire placed at the top of the slots
C) Thin wire placed at the bottom of the slots
D) Thin wire placed at the top of the slots
Explanation: The main winding uses thick wire placed at the bottom of the slots to handle higher current.
In case of high speed universal motor which of the following needs more attention?
A) Air gap
B) Balancing of rotor
C) End play
D) Insulation in rotor
Explanation: Rotor balancing is critical in high-speed universal motors to prevent vibrations.
The wattage of the motor for driving a domestic sewing machine will be around
A) 10 to 30 W
B) 40 to 75 W
C) 100 to 150 W
D) 5 to 10 W
Explanation: Domestic sewing machines typically use motors in the range of 40 to 75 watts.
By pushing and pulling the rotor shaft of a motor, we can check its
A) None of these answers
B) Side play
C) Firmness of mounting
D) Free shaft movement
E) End play
Explanation: Pushing and pulling the shaft checks for free movement and end play.
Two-value capacitor motor finds increased application as compressor motor in small home air conditioners because
A) It is quiet in operation
B) It has an almost non-destructible capacitor
C) It is comparatively cheaper
D) It has low starting as well as running currents at a relatively high power factor
Explanation: Two-value capacitor motors are efficient and provide high power factor, making them suitable for compressors.
A capacitor selected for capacitor-run motor should be rated for
A) R.M.S. voltage
B) None of these answers
C) Average voltage
D) Peak voltage
Explanation: Capacitors for capacitor-run motors are rated for RMS voltage to ensure safe operation.
In which single-phase motor, the rotor has no teeth or winding?
A) Universal motor
B) Hysteresis motor
C) Reluctance motor
D) Split phase motor
Explanation: The rotor in a hysteresis motor is smooth and has no teeth or windings.
The wattage rating for a ceiling fan motor will be in the range
A) 250 to 500 W
B) 10 to 20 W
C) 50 to 150 W
D) 200 to 250 W
Explanation: Ceiling fan motors typically have a wattage rating of 50 to 150 watts.
Which of the following applications make use of a universal motor?
A) Portable tools
B) Floor polishing machine
C) Lathe machines
D) Oil expeller
Explanation: Universal motors are commonly used in portable tools due to their high-speed operation.
Which of the following statements regarding a reluctance motor is incorrect?
A) It cannot be reversed, ordinarily
B) Its squirrel cage-rotor is of unsymmetrical magnetic construction in order to vary reluctance path between stator and rotor
C) It requires no D.C. excitation for its operation
D) It is nothing else but a single-phase, salient pole synchronous-induction motor
Explanation: Reluctance motors are not synchronous-induction motors; they are a separate category.
The speed with which the magnetic field of an induction motor rotates is called
A) Shaft speed
B) Slip speed
C) Effective speed
D) Synchronous speed
Explanation: The magnetic field rotates at synchronous speed, which is determined by the supply frequency and number of poles.
Which of the following motors has the highest starting torque?
A) Split-phase motor
B) Repulsion motor
C) Capacitor-start motor
D) Shaped pole motor
Explanation: Capacitor-start motors provide high starting torque due to the phase shift created by the capacitor.
Starting winding of a single-phase motor of a refrigerator is disconnected from the circuit by means of a
A) Centrifugal switch
B) None of these answers
C) Magnetic relay
D) Thermal relay
Explanation: A centrifugal switch disconnects the starting winding once the motor reaches a certain speed.
In a shaded pole motor, the direction of rotation is from
A) Main pole to shaded pole
B) Shaded pole to the main pole
C) None of these answers
D) Depends on supply line polarity
Explanation: The motor rotates from the main pole to the shaded pole due to the phase shift created by the shading coil.
Which of the following single-phase induction motors is generally used in time phonographs?
A) Resistance start
B) Shaded pole
C) Capacitor start capacitor run
D) Universal
Explanation: Shaded pole motors are commonly used in phonographs due to their simplicity and quiet operation.
When a universal motor is operated on no-load, its speed is limited by
A) Weight of the armature
B) Windage and friction
C) Supply voltage frequency
D) Armature reaction
Explanation: On no-load, the speed of a universal motor is limited by windage and friction losses.
Most of the fractional horsepower motors have either
A) Ball or roller bearings
B) Plain or sleeve bearings
C) Hard and annealed bearings
D) Soft and porous bearings
Explanation: Fractional horsepower motors typically use plain or sleeve bearings for cost-effectiveness.
In a split phase motor
A) The starting winding is connected through a centrifugal switch
B) The running winding is connected through a centrifugal switch
C) The centrifugal switch is used to control supply voltage
D) Both starting and running windings are connected through a centrifugal switch
Explanation: The starting winding is connected through a centrifugal switch, which disconnects it once the motor reaches a certain speed.
If the ceiling fan, when switched on, runs at a slow speed in the reverse direction, it can be concluded that
A) None of these answers
B) The winding has burnt out
C) Capacitor is ineffective
D) Bearings are worn out
Explanation: A faulty or ineffective capacitor can cause the fan to run slowly in the reverse direction.
The rotor of the hysteresis motor is made of
A) Chrome steel
B) Aluminum
C) Copper
D) Cast iron
Explanation: The rotor is made of chrome steel, which has high hysteresis loss properties.
The motor used for the compressors is
A) Reluctance motor
B) D.C. series motor
C) Shaded pole motor
D) Capacitor-start capacitor-run motor
Explanation: Capacitor-start capacitor-run motors are commonly used in compressors due to their high starting torque and efficiency.
Which motor is normally free from mechanical and magnetic vibrations?
A) Split phase motor
B) Hysteresis motor
C) Shaded pole motor
D) Universal motor
Explanation: Hysteresis motors operate smoothly without mechanical or magnetic vibrations.
In a split phase motor, the running winding should have
A) Low resistance and high inductance
B) High resistance as well as high inductance
C) Low resistance as well as low inductance
D) High resistance and low inductance
Explanation: The running winding has low resistance and high inductance to ensure proper phase shift.
The speed of a universal motor is generally reduced by using
A) Gear trains
B) V-belts
C) Chains
D) Brakes
Explanation: Gear trains are commonly used to reduce the speed of universal motors.
A hysteresis motor works on the principle of
A) Hysteresis loss
B) Electromagnetic induction
C) Magnetization of rotor
D) Eddy current loss
Explanation: Hysteresis motors operate based on hysteresis loss in the rotor material.
In an A.C. series motor armature coils are usually connected to the commutator
A) Through capacitors
B) Solidly
C) Through reactances
D) Through resistance
Explanation: Armature coils are solidly connected to the commutator in AC series motors.
The capacitors used in, single-phase capacitor motors have no
A) Definite value
B) Polarity marking
C) Dielectric medium
D) Voltage rating
Explanation: Capacitors used in single-phase motors are non-polarized and do not have polarity markings.
In a ceiling fan employing capacitor run motor
A) Primary winding surrounds the secondary winding
B) Both are usual arrangements
C) None of these answers
D) Secondary winding surrounds the primary winding
Explanation: In capacitor-run motors, the secondary winding typically surrounds the primary winding.
The starting winding of a single-phase motor is placed in
A) Stator
B) Armature
C) Field
D) Rotor
Explanation: The starting winding is located in the stator of a single-phase motor.
Which of the following motors has two separate windings on the motor?
A) Repulsion induction motor
B) None of these answers
C) Repulsion motor
D) Repulsion start induction run motor
Explanation: Repulsion start induction run motors have two separate windings for starting and running.
A shaded pole motor can be used for
A) Any of these answers
B) Toys
C) Hair dryers
D) Circulators
Explanation: Shaded pole motors are versatile and can be used in toys, hair dryers, and circulators.
A single-phase capacitor-start motor will take starting current nearly
A) Same as full load current
B) Four to six times the full load current
C) Twice the full load current
D) Three times the full load current
Explanation: Capacitor-start motors draw 4-6 times the full load current during starting.
The direction of rotation of the universal motor can be reversed by
A) Interchanging the brush leads
B) Reversing the supply terminals
C) Switching over from A.C. to D.C.
D) Any of these answers
Explanation: The direction of a universal motor can be reversed by reversing the brush leads, supply terminals, or switching between AC and DC.
In a universal motor, normally the ratio of the width of the brush to the width of commutator segments is
A) 2 : 1
B) 4 : 1
C) 6 : 1
D) 1 : 1
Explanation: The brush width is typically four times the width of the commutator segments in universal motors.