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D.C. Motors

Study 130 Electrical Engineering MCQs with correct answers and explanations.

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11Electrical EngineeringMedium

Which of the following motor has the poorest speed regulation?

ACumulative compound motor

BShunt motor

CSeries motor

DDifferential compound motor

Correct answer

C. Series motor

Explanation

The correct answer is Series motor.

12Electrical EngineeringMedium

The speed of a D.C. shunt motor more than its full-load speed can be obtained by________?

Aincreasing the armature current

Bdecreasing the field current

Cdecreasing the armature current

Dincreasing the field current

Correct answer

B. decreasing the field current

Explanation

The correct answer is decreasing the field current.

13Electrical EngineeringMedium

The hysteresis loss in a D.C. machine least depends on________?

AVolume and grade of iron

BRate of flow of ventilating air

CFrequency of magnetic reversals

DMaximum value of flux density

Correct answer

B. Rate of flow of ventilating air

Explanation

The correct answer is Rate of flow of ventilating air.

14Electrical EngineeringMedium

For a D.C. shunt motor if the excitation is changed________?

Atorque will remain constant

Btorque and power both will change

Ctorque, power and speed, all will change

Dtorque will change but power will remain constant

Correct answer

D. torque will change but power will remain constant

Explanation

The correct answer is torque will change but power will remain constant.

15Electrical EngineeringMedium

Differentially compound D.C. motors can find applications requiring________?

Avariable speed

Bfrequent on-off cycles

Clow starting torque

Dhigh starting torque

Correct answer

C. low starting torque

Explanation

The correct answer is low starting torque.

16Electrical EngineeringMedium

D.C. series motors are used________?

Awhere constant operating speed is needed

Bwhere load is constant

Cwhere load changes frequently

Din none of the above situations

Correct answer

D. in none of the above situations

Explanation

The correct answer is in none of the above situations.

17Electrical EngineeringMedium

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________?

Aa resistance is connected in series with armature

Barmature is temporarily open circuited

Ca high value resistor is connected across the field winding

Da resistance is connected parallel to the armature

Correct answer

A. a resistance is connected in series with armature

Explanation

The correct answer is a resistance is connected in series with armature.

18Electrical EngineeringMedium

Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control________?

Athree point starter is used

Ball above can be used

Cdrum type controller is used

Dfour point starter is used

Correct answer

C. drum type controller is used

Explanation

The correct answer is drum type controller is used.

19Electrical EngineeringMedium

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

Aself-induced e.m.f.

Bback e.m.f

Cnone of the above

Dmutually induced e.m.f.

Correct answer

B. back e.m.f

Explanation

The correct answer is back e.m.f.

20Electrical EngineeringMedium

In a D.C. shunt motor, speed is________?

Ainversely proportional to the armature current

Bdirectly proportional to the armature current

Cindependent of armature current

Dproportional to the square of the current

Correct answer

C. independent of armature current

Explanation

The correct answer is independent of armature current.

For a D.C. shunt motor if the excitation is changed________?

Atorque will remain constant

Btorque and power both will change

Ctorque, power and speed, all will change

Dtorque will change but power will remain constant

Correct answer

D. torque will change but power will remain constant

Explanation

The correct answer is torque will change but power will remain constant.

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________?

Aa resistance is connected in series with armature

Barmature is temporarily open circuited

Ca high value resistor is connected across the field winding

Da resistance is connected parallel to the armature

Correct answer

A. a resistance is connected in series with armature

Explanation

The correct answer is a resistance is connected in series with armature.