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D.C. Motors

Study 130 Electrical Engineering MCQs with correct answers and explanations.

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101Electrical EngineeringMedium

If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens________?

Athis will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed

Bthis will make armature to take heavy current, possibly burning it

Cnothing will happen to the motor

Correct answer

A. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed

Explanation

The correct answer is this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed.

102Electrical EngineeringMedium

Which of the following motor is preferred for operation in highly explosive atmosphere?

AAir motor

BBattery operated motor

CShunt motor

DSeries motor

Correct answer

A. Air motor

Explanation

The correct answer is Air motor.

103Electrical EngineeringMedium

For which types of D.C. motor, dynamic braking is generally used?

AAll of the above

BShunt motors

CSeries motors

DCompound motors

Correct answer

A. All of the above

Explanation

The correct answer is All of the above.

104Electrical EngineeringMedium

The condition for maximum power in case of D.C. motor is________?

Aback e.m.f. = | x supply voltage

Bback e.m.f. = 2 x supply voltage

Csupply voltage = | x back e.m.f

Dsupply voltage = back e.m.f

Correct answer

A. back e.m.f. = | x supply voltage

Explanation

The correct answer is back e.m.f. = | x supply voltage.

105Electrical EngineeringMedium

For the same H.P. rating and full load speed, following motor has poor starting torque________?

Acumulativelyc’ompounded

Bseries

Cshunt

Ddifferentially compounded

Correct answer

D. differentially compounded

Explanation

The correct answer is differentially compounded.

106Electrical EngineeringMedium

Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator?

AUsing material of low hysteresis co-efficient for armature core material

BProviding laminations in armature core

CUsing non-magnetic material for frame

DProviding laminations in stator

Correct answer

A. Using material of low hysteresis co-efficient for armature core material

Explanation

The correct answer is Using material of low hysteresis co-efficient for armature core material.

107Electrical EngineeringMedium

Which of the following method is used for the speed control of DC shunt motor?

Avoltage control method

Bflux control method

Call of the above

Drheostat control method

Correct answer

C. all of the above

Explanation

The correct answer is all of the above.

108Electrical EngineeringMedium

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

Aalmost negligible

Bmore than full-load current

Cless than full-load current

Drated full-load current

Correct answer

B. more than full-load current

Explanation

The correct answer is more than full-load current.

109Electrical EngineeringMedium

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

AVariable speed operation

BFixed speed operation

CLow speed operation

DHigh speed operation

Correct answer

A. Variable speed operation

Explanation

The correct answer is Variable speed operation.

110Electrical EngineeringMedium

Which of the following test can be performed on DC series motor?

ABrake test

BHopkinson test

CField test

DSwinburne test

Correct answer

C. Field test

Explanation

The correct answer is Field test.

If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens________?

Athis will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed

Bthis will make armature to take heavy current, possibly burning it

Cnothing will happen to the motor

Correct answer

A. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed

Explanation

The correct answer is this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed.

Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator?

AUsing material of low hysteresis co-efficient for armature core material

BProviding laminations in armature core

CUsing non-magnetic material for frame

DProviding laminations in stator

Correct answer

A. Using material of low hysteresis co-efficient for armature core material

Explanation

The correct answer is Using material of low hysteresis co-efficient for armature core material.