DMRC JE/SSC JE/CIL MT ELECTRICAL ENGINEERING IMPORTANT MCQ PART 7(DC MOTORS)

1.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
ANSWER : : Armature control method
2.Sparking, is discouraged in a D.C. motor because
it increases the input power con-sumption
commutator gets damaged
both (a) and (b)
none of the above
ANSWER : : commutator gets damaged
3.The speed of a D.C. motor can be varied by varying
field current
applied voltage
resistance in series with armature
any of the above
ANSWER : : any of the above
4.If I be the armature current, then speed of a D.C. shunt motor is
independent of Ia
proportional to la
varies as (Ia)
none of these
ANSWER : : independent of Ia
5.Which D.C. motor is generally preferred for cranes and hoists ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor
ANSWER : : Series motor 

6.Speed control by Ward Leonard method gives uniform speed variation
in one direction
in both directions
below normal speed only
above normal speed only.
ANSWER : : in both directions
7.Which of the following motor has the poorest speed regulation ?
Shunt motor
Series motor
Differential compound motor
Cumulative compound motor
ANSWER : : Series motor
8.Three point starter can be used for
series motor only
shunt motor only
compound motor only
both shunt and compound motor
ANSWER : : both shunt and compound motor
9.Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have
to be
level compounded
under compounded
cumulatively compounded
differentially compounded
ANSWER : : cumulatively compounded
10.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.
ANSWER : : Low cost 

11.Following motor is used where high starting torque and wide speed range control is required.
Single phase capacitor start
Induction motor
Synchronous motor
D.C. motor
ANSWER : : D.C. motor
12.At the instant of starting when a D.C. motor is put on supply, it behaves like
a highly resistive circuit
a low resistance circuit
a capacitive circuit
none of the above
ANSWER : : a low resistance circuit
13.As -the load is increased the speed of D.C. shunt motor will
reduce slightly
increase slightly
increase proportionately
remains unchanged
ANSWER : : reduce slightly
14.In D.C. machines the residual magnetism is of the order of
2 to 3 per cent
10 to 15 per cent
20 to 25 per cent
50 to 75 per cent
ANSWER : : 2 to 3 per cent
15.The armature voltage control of D.C. motor provides
constant torque drive
constant voltage drive
constant current drive
none of the above
ANSWER : : constant torque drive

16.For a D.C. shunt motor if the excitation is changed
torque will remain constant
torque will change but power will remain constant
torque and power both will change
torque, power and speed, all will change
ANSWER : : torque will change but power will remain constant
17.Usually wide and sensitive speed control is desired in case of
centrifugal pumps
elevators
steel rolling mills
colliery winders
ANSWER : : colliery winders
18.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
ANSWER : : a resistance is connected in series with armature
19.In a differentially compounded D.C. motor, if shunt field suddenly opens
the motor will first stop and then run in opposite direction as series motor
the motor will work as series motor and run at slow speed in the same direction
the motor will work as series motor and run at high speed in the same direction
the motor will not work and come to stop
ANSWER : : the motor will first stop and then run in opposite direction as series motor
20.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
ANSWER : : increasing the resistance in field circuit
21.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
ANSWER : : armature current only
22.In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
remain unchanged
reduce to one-fourth value
increase four folds
be doubled
ANSWER : : remain unchanged
23.The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
2.36%
4.76%
6.77%
8.84%
ANSWER : : 4.76%
24.Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
D.C. series motor
D.C. shunt motor
induction motor
all of above motors
ANSWER : : D.C. series motor

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CURRENT AFFAIRS QUIZ OF DAY-5 February 2017
DMRC JE/SSC JE/CIL MT ELECTRICAL ENGINEERING IMPORTANT MCQ PART 6(DC MOTORS)

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