Practice D.C. Motors Multiple Choice Questions Quiz-3 - MCQGeeks.com

Q.1

D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the

Series motor
Shunt motor
Compound motor
Any of the above

Q.2

The speed of a D.C. shunt motor can be increased by

Increasing the resistance in armature circuit
Increasing the resistance in field circuit
Reducing the resistance in the field circuit
Reducing the resistance in the armature circuit

Q.3

The armature voltage control of D.C. motor provides

Constant torque drive
Constant voltage drive
Constant current drive
None of the above

Q.4

Starters are used with D.C. motors because

These motors have high starting torque
These motors are not self-starting
Back e.m.f. of these motors is zero initially
To restrict armature current as there is no back e.m.f. while starting

Q.5

Which of the following method of speed control of D.C. machine will offer minimum efficiency?

Voltage control method
Field control method
Armature control method
All above methods

Q.6

A D.C. series motor is that which

Has its field winding consisting of thick wire and less turns
Has a poor torque
Can be started easily without load
Has almost constant speed

Q.7

D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this

Series motor
Shunt motor
Compound motor
Any of the above

Q.8

Which of the following motor has the poorest speed regulation?

Shunt motor
Series motor
Differential compound motor
Cumulative compound motor

Q.9

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

Field copper loss
Windage loss
Armature copper loss
None of the above

Q.10

For starting a D.C. motor a starter is required because

It limits the speed of the motor
It limits the starting current to a safe value
It starts the motor
None of the above

Q.11

In D.C. motor which of the following can sustain the maximum temperature rise?

Slip rings
Commutator
Field winding
Armature winding

Q.12

In variable speed motor

A stronger commutating field is needed at low speed than at high speed
A weaker commutating field is needed at low speed than at high speed
Same commutating field is needed at low speed than at high speed
None of the above is correct

Q.13

Usually wide and sensitive speed control is desired in case of

Centrifugal pumps
Elevators
Steel rolling mills
Colliery winders

Q.14

Which one of the following is not the function of pole shoes in a D.C. machine?

To reduce eddy current loss
To support the field coils
To spread out flux for better uniformity
To reduce the reluctance of the magnetic path

Q.15

In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to

100% of the previous value
50% of the previous value
25% of the previous value
10% of the previous value

Q.16

No-load speed of which of the following motor will be highest?

Shunt motor
Series motor
Cumulative compound motor
Differentiate compound motor

Q.17

D.C. series motors are used

Where load is constant
Where load changes frequently
Where constant operating speed is needed
In none of the above situations

Q.18

Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors?

Low cost
Wide speed range
Stability
High starting torque

Q.19

The armature torque of the D.C. shunt motor is proportional to

field flux only
armature current only
both (A) and (B)
none of the above

Q.20

If the supply voltage for a D.C. motor is increased, which of the following will decrease?

Starting torque
Operating speed
Full-load current
All of the above

Q.21

Sparking at the commutator of a D.C. motor may result in

Damage to commutator segments
Damage to commutator insulation
Increased power consumption
All of the above

Q.22

For which of the following applications a D.C. motor is preferred over an A.C. motor?

Low speed operation
High speed operation
Variable speed operation
Fixed speed operation

Q.23

As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit

A resistance is connected in series with armature
A resistance is connected parallel to the armature
Armature is temporarily open circuited
A high value resistor is connected across the field winding

Q.24

In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be

Almost negligible
Rated full-load current
Less than full-load current
More than full-load current

Q.25

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

Regenerative
Plugging
Dynamic braking
None of the above

Q.26

If a D.C. motor is to be selected for conveyors, which motor would be preferred ?

Series motor
Shunt motor
Differentially compound motor
Cumulative compound motor

Q.27

Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity?

Swinburne's test
Hopkinson's test
Field test
Brake test

Q.28

When the armature of a D.C. motor rotates, e.m.f. induced is

Self-induced e.m.f.
Mutually induced e.m.f.
Back e.m.f.
None of the above

Q.29

The power mentioned on the name plate of an electric motor indicates

The power drawn in kW
The power drawn in kVA
The gross power
The output power available at the shaft

Q.30

If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor

Of lower H.P. should be selected
Of higher H.P. should be selected
Can be used for 50°C ambient temperature also
Is to be de-rated by a factor recommended by manufacturer and select the next higher H.P. motor

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