Engineering/Engineering Electrical Engineering Dc Motors part 2 Sample Test,Sample questions

Question:
.In case the back e.m.f. and the speed of a D.C. motor are doubled the torque developed by the motor will

1.remain unchanged

2.reduce to one-fourth value

3.increase four folds

4.be doubled


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

1.Low cost

2.Wide speed range

3.Stability

4.High starting torque.


Question:
As -the load is increased the speed of D.C. shunt motor will

1.reduce slightly

2.increase slightly

3.increase proportionately

4.remains unchanged


Question:
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

1.a resistance is connected in series with armature

2.a resistance is connected parallel to the armature

3.armature is temporarily open circuited

4.a high value resistor is connected across the field winding


Question:
At the instant of starting when a D.C. motor is put on supply it behaves like

1.a highly resistive circuit

2.a low resistance circuita highly resistive circuit

3.a capacitive circuit

4.None of the above


Question:
Buses trains trolleys hoists cranes require high starting torque and therefore make use of

1.D.C. series motor

2.D.C. shunt motor

3.induction motor

4.all of above motors


Question:
D.C. shunt motors are used for driving

1.trains

2.cranes

3.hoists

4.machine tools


Question:
Flywheel is used with D.C. compound motor to reduce the peak demand by the motor compound motor will have to be

1.level compounded

2.under compounded

3.cumulatively compounded

4.differentially compounded


Question:
Following motor is used where high starting torque and wide speed range control is required.

1.Single phase capacitor start

2.Induction motor

3.Synchronous motor

4.D.C. motor


Question:
For a D.C. shunt motor if the excitation is changed

1.torque will remain constant

2.torque will change but power will remain constant

3.torque and power both will change

4.torque power and speed all will change


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

1.of lower H.P. should be selected

2.of higher H.P. should be selected

3.can be used for 50 C ambient temperature also

4.is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor


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

1.increase

2.decrease

3.remain same

4.become zero


Question:
In a differentially compounded D.C. motor if shunt field suddenly opens

1.the motor will first stop and then run in opposite direction as series motor

2.the motor will work as series motor and run at slow speed in the same direction

3.the motor will work as series motor and run at high speed in the same direction

4.the motor will not work and come to stop


Question:
In D.C. machines the residual magnetism is of the order of

1.2 to 3 per cent

2.10 to 15 per cent

3.20 to 25 per cent

4.50 to 75 per cent


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

1.residual magnetism of the generator

2.core losses of motor

3.mechanical losses of motor and gen erator together

4.all of the above


Question:
Regenerative method of braking is based on that

1.back e.m.f. is less than the applied voltage

2.back e.m.f. is equal to the applied voltage

3.back e.m.f. of rotor is more than the applied voltage

4.none of the above


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

1.field flux only

2.armature current only

3.both (a) and (b)

4.None of the above


Question:
The armature voltage control of D.C. motor provides

1.constant torque drive

2.constant voltage drive

3.constant current drive

4.None of the above


Question:
The armature voltage control of D.C. motor provides

1.constant voltage drive

2.constant current drive

3.constant torque drive

4.None of the above


Question:
The main disadvantage of the Ward-Leonard control method is

1.high initial cost

2.high maintenance cost

3.low efficiency at Hght loads

4.all of the above


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

1.increasing the resistance in armature circuit

2.increasing the resistance in field circuit

3.reducing the resistance in the field circuit

4.reducing the resistance in the armature circuit


Question:
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

1.2.36%

2.4.76%

3.6.77%

4.8.84%


Question:
Three point starter can be used for

1.series motor only

2.shunt motor only

3.compound motor only

4.both shunt and compound motor


Question:
Usually wide and sensitive speed control is desired in case of

1.centrifugal pumps

2.elevators

3.steel rolling mills

4.colliery winders


Question:
Ward-Leonard control is basically a

1.voltage control method

2.field divertor method

3.field control method

4.armature resistance control method


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

1.Field copper loss

2.Windage loss

3.Armature copper loss

4.None of the above


Question:
Which of the following motor has the poorest speed regulation ?

1.Shunt motor

2.Series motor

3.Differential compound motor

4.Cumulative compound motor


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

1.D.C. shunt motor

2.D.C. series motor

3.Induction motor

4.Reluctance motor


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

1.D.C. shunt motor

2.D.C. series motor

3.Single phase induction motor (split phase start or induction run motor)

4.Reluctance motor


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

1.D.C. shunt motor

2.D.C. series motor

3.Universal motor

4.Synchronous motor


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