DMRC JE/SSC JE/CIL MT ELECTRICAL ENGINEERING IMPORTANT MCQ PART 8(DC MOTORS)

1.The armature voltage control of D.C. motor provides
constant voltage drive
constant current drive
constant torque drive
none of the above
ANSWER : : constant torque drive
2.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
ANSWER : : Armature copper loss
3.Which of the following motors is most suitable for signalling devices and many kinds of timers ?
D.C. shunt motor
D.C. series motor
Induction motor
Reluctance motor
ANSWER : : Reluctance motor
4.If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
increase
decrease
remain same
become zero
ANSWER : : increase
5.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 50C ambient temperature also
is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor
ANSWER : : is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor 

6.D.C. shunt motors are used for driving
trains
cranes
hoists
machine tools
ANSWER : : machine tools
7.The main disadvantage of the Ward-Leonard control method is
high initial cost
high maintenance cost
low efficiency at Hght loads
all of the above
ANSWER : : all of the above
8.Which of the following motors is usually used in house-hold refrigerators ?
D.C. shunt motor
D.C. series motor
Single phase induction motor (split phase start or induction run motor)
Reluctance motor
ANSWER : : Single phase induction motor (split phase start or induction run motor)
9.Regenerative method of braking is based on that
back e.m.f. is less than the applied voltage
back e.m.f. is equal to the applied voltage
back e.m.f. of rotor is more than the applied voltage
none of the above
ANSWER : : back e.m.f. is equal to the applied voltage
10.In Ward-Leonard control the lower limit of speed is imposed by
residual magnetism of the generator
core losses of motor
mechanical losses of motor and generator together
all of the above
ANSWER : : residual magnetism of the generator 

11.Ward-Leonard control is basically a
voltage control method
field divertor method
field control method
armature resistance control method
ANSWER : : voltage control method
12.Which of the following motors one will choose to drive the rotary compressor ?
D.C. shunt motor
D.C. series motor
Universal motor
Synchronous motor
ANSWER : : Synchronous motor
13.Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
Providing laminations in armature core
Providing laminations in stator
Using non-magnetic material for frame
Using material of low hysteresis co-efficient for armature core material
ANSWER : : Using material of low hysteresis co-efficient for armature core material
14.Which of the following loss in a D.C. generator is dissipated in the form of heat?
Mechanical loss
Core loss
Copper loss
All of the above
ANSWER : : All of the above
15.In a D.C. generator all of the following could be the effects of iron losses except
Loss of efficiency
Excessive heating of core
Increase in terminal voltage
Rise in temperature of ventilating air
ANSWER : : Increase in terminal voltage
16.For constant torque drive which speed control method is preferred ?
Field control
Armature voltage control
Shunt armature control
Mechanical loading system
ANSWER : : Armature voltage control
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 ?
hysteresis loss
field copper loss
armature copper loss
eddy current loss
ANSWER : : armature copper loss
18.The hysteresis loss in a D.C. machine least depends on
Frequency of magnetic reversals
Maximum value of flux density
Volume and grade of iron
Rate of flow of ventilating air
ANSWER : : Rate of flow of ventilating air
19.Which motor should not be started on no-load ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor.
ANSWER : : Series motor
20.If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
plugging
dynamic braking
none of the above
any of the above
ANSWER : : plugging 

21.In a manual shunt motor starter
over load relay is connected in series and no volt relay in parallel with the load
over load relay is connected in parallel and no volt relay in series with the load
over load relay and no volt relay are both connected in series with the load
over load relay and no volt relay are both connected in parallel with the load
ANSWER : : over load relay is connected in series and no volt relay in parallel with the load
22.Why are the D.C. motors preferred for traction applications ?
Torque and speed are inversely proportional to armature current
Torque is proportional to armature current
Torque is proportional to square root of armature current
The speed is inversely proportional to the torque and the torque is proportional to square of armature current
ANSWER : : The speed is inversely proportional to the torque and the torque is proportional to square of armature current
23.The plugging gives the
zero torque braking
smallest torque braking
highest torque braking
none of the above
ANSWER : : highest torque braking
24.Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
Hysteresis losses
Eddy current losses
Copper losses
Windage losses
ANSWER : : Eddy current losses

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DMRC JE/SSC JE/CIL MT ELECTRICAL ENGINEERING IMPORTANT MCQ PART 9(DC MOTORS)
सौरमंडल (Solar System )

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