Question 1

The plugging gives the
A)zero torque braking
B)smallest torque braking
C)highest torque braking
D)none of the above

Accepted Answer

Plugging is a method used in electric motors to achieve rapid braking by reversing the motor's direction of rotation. This method generates the highest torque braking compared to other electric braking methods like dynamic braking or regenerative braking, effectively bringing the motor to a stop quickly.

Question 2

The armature voltage control of D.C. motor provides
A)constant voltage drive
B)constant current drive
C)constant torque drive
D)none of the above

Accepted Answer

The armature voltage control of a DC motor adjusts the voltage applied to the armature, which directly affects the motor's speed. Since torque in a DC motor is proportional to the armature current (assuming a constant field flux), and the armature current is influenced by the armature voltage, controlling the armature voltage can maintain a constant torque under varying load conditions, provided the motor is not operating in the saturation region of its magnetic circuit.

Question 3

If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
A)regenerative
B)plugging
C)dynamic braking
D)none of the above

Accepted Answer

Interchanging the terminals of the armature of a DC motor results in plugging, which reverses the direction of the motor's current, creating a braking force that opposes the motor's rotation.

Question 4

Which of the following motors one will choose to drive the rotary compressor ?
A)D.C. shunt motor
B)D.C. series motor
C)Universal motor
D)Synchronous motor

Accepted Answer

The answer of Which of the following motors one will...

Question 5

If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
A)increase
B)decrease
C)remain same
D)become zero

Accepted Answer

The back electromotive force (e.m.f.) in a DC shunt motor is directly proportional to the speed of the motor. Therefore, if the speed increases, the back e.m.f. also increases.

Question 6

Why are the D.C. motors preferred for traction applications ?
A)Torque and speed are inversely proportional to armature current
B)Torque is proportional to armature current
C)Torque is proportional to square root of armature current
D)The speed is inversely proportional to the torque and the torque is proportional to square of armature current

Accepted Answer

The answer of Why are the D.C. motors preferred for...

Question 7

Which of the following motors is usually used in house-hold refrigerators ?
A)D.C. shunt motor
B)D.C. series motor
C)Single phase induction motor (split phase start or induction run motor)
D)Reluctance motor

Accepted Answer

Single phase induction motors, particularly the split phase start or induction run types, are commonly used in household refrigerators. This is because they are well-suited for running at a constant speed and do not require the direction changes or variable speed control that DC motors offer. Additionally, they are simpler and more cost-effective for AC power systems, which are standard in homes.

Question 8

Which of the following motors is most suitable for signalling devices and many kinds of timers ?
A)D.C. shunt motor
B)D.C. series motor
C)Induction motor
D)Reluctance motor

Accepted Answer

Reluctance motors are most suitable for signalling devices and many kinds of timers due to their precise control and ability to hold a position without a holding current, making them ideal for applications requiring precise movements and timing.

Question 9

Which motor should not be started on no-load ?
A)Series motor
B)Shunt motor
C)Cumulatively compounded motor
D)Differentially compounded motor.

Accepted Answer

Series motors should not be started on no-load because they can potentially run at dangerously high speeds under no-load conditions, which can cause damage to the motor.

Question 10

Ward-Leonard control is basically a
A)voltage control method
B)field divertor method
C)field control method
D)armature resistance control method

Accepted Answer

Ward-Leonard control is a voltage control method used for controlling the speed of DC motors by varying the armature voltage.

Question 11

For constant torque drive which speed control method is preferred ?
A)Field control
B)Armature voltage control
C)Shunt armature control
D)Mechanical loading system

Accepted Answer

Armature voltage control is preferred for constant torque drive as it allows for smooth speed variation while maintaining constant torque.

Question 12

In Ward-Leonard control the lower limit of speed is imposed by
A)residual magnetism of the generator
B)core losses of motor
C)mechanical losses of motor and gen¬erator together
D)all of the above

Accepted Answer

The lower limit of speed in Ward-Leonard control is primarily imposed by the residual magnetism of the generator, as it affects the minimum voltage that can be generated, thus limiting the minimum speed.

Question 13

The main disadvantage of the Ward-Leonard control method is
A)high initial cost
B)high maintenance cost
C)low efficiency at Hght loads
D)all of the above

Accepted Answer

The Ward-Leonard control method involves significant initial investment in equipment, requires regular maintenance due to its mechanical and electrical components, and can be less efficient at light loads due to its continuous operation of the motor-generator set, making all of the options correct.

Question 14

Regenerative method of braking is based on that
A)back e.m.f. is less than the applied voltage
B)back e.m.f. is equal to the applied voltage
C)back e.m.f. of rotor is more than the applied voltage
D)none of the above

Accepted Answer

The answer of Regenerative method of braking is based on...

Question 15

The hysteresis loss in a D.C. machine least depends on
A)Frequency of magnetic reversals
B)Maximum value of flux density
C)Volume and grade of iron
D)Rate of flow of ventilating air

Accepted Answer

Hysteresis loss in a DC machine is primarily dependent on the frequency of magnetic reversals, the maximum value of flux density, and the volume and grade of iron. The rate of flow of ventilating air does not significantly affect hysteresis loss, as this loss is related to the magnetic properties of the material and not to cooling or ventilation conditions.

Question 16

In a D.C. generator all of the following could be the effects of iron losses except
A)Loss of efficiency
B)Excessive heating of core
C)Increase in terminal voltage
D)Rise in temperature of ventilating air

Accepted Answer

Iron losses in a D.C. generator, which include hysteresis and eddy current losses, lead to a loss of efficiency, excessive heating of the core, and a rise in temperature of ventilating air. However, they do not cause an increase in terminal voltage; instead, they can contribute to a decrease in efficiency and output voltage due to the energy dissipated as heat.

Question 17

The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
A)hysteresis loss
B)field copper loss
C)armature copper loss
D)eddy current loss

Accepted Answer

At rated load, the armature copper loss, which is proportional to the square of the armature current, tends to be the highest among the losses listed, as the generator operates at its full current capacity.

Question 18

Which of the following loss in a D.C. generator varies significantly with the load current ?
A)Field copper loss
B)Windage loss
C)Armature copper loss
D)None of the above

Accepted Answer

Armature copper loss varies significantly with the load current because it is directly proportional to the square of the current flowing through the armature winding.

Question 19

Torque developed by a D.C. motor depends upon
A)magnetic field
B)active length of the conductor
C)current flow through the conductors
D)all above factors

Accepted Answer

The torque developed by a DC motor is directly proportional to the magnetic field strength, the active length of the conductor (which is part of the motor's armature), and the current flowing through the conductors. All these factors collectively determine the torque produced by the motor.

Question 20

D.C. shunt motors are used for driving
A)trains
B)cranes
C)hoists
D)machine tools

Accepted Answer

D.C. shunt motors are used for driving machine tools because they provide a nearly constant speed under varying load conditions, which is ideal for applications requiring precise speed control.

Quiz 4: D.C. Motors and Generators

The plugging gives the

The armature voltage control of D.C. motor provides

If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking

Which of the following motors one will choose to drive the rotary compressor ?

If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will

Why are the D.C. motors preferred for traction applications ?

Which of the following motors is usually used in house-hold refrigerators ?

Which of the following motors is most suitable for signalling devices and many kinds of timers ?

Which motor should not be started on no-load ?

Ward-Leonard control is basically a

For constant torque drive which speed control method is preferred ?

In Ward-Leonard control the lower limit of speed is imposed by

The main disadvantage of the Ward-Leonard control method is

Regenerative method of braking is based on that

The hysteresis loss in a D.C. machine least depends on

In a D.C. generator all of the following could be the effects of iron losses except

The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?

Which of the following loss in a D.C. generator varies significantly with the load current ?

Torque developed by a D.C. motor depends upon

D.C. shunt motors are used for driving