DC Motors Mcqs - Set 5

1)   Why are the D.C. motors preferred for traction applications ?

a. Torque and speed are inversely proportional to armature current
b. Torque is proportional to armature current
c. Torque is proportional to square root of armature current
d. The speed is inversely proportional to the torque and the torque is proportional to square of armature current
Answer  Explanation 

ANSWER: The speed is inversely proportional to the torque and the torque is proportional to square of armature current

Explanation:
No explanation is available for this question!


2)   Which of the following motors is usually used in house-hold refrigerators ?

a. D.C. shunt motor
b. D.C. series motor
c. Single phase induction motor (split phase start or induction run motor)
d. Reluctance motor
e. Synchronous motor
Answer  Explanation 

ANSWER: Single phase induction motor (split phase start or induction run motor)

Explanation:
No explanation is available for this question!


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

a. D.C. shunt motor
b. D.C. series motor
c. Induction motor
d. Reluctance motor
Answer  Explanation 

ANSWER: Reluctance motor

Explanation:
No explanation is available for this question!


4)   Which motor should not be started on no-load ?

a. Series motor
b. Shunt motor
c. Cumulatively compounded motor
d. Differentially compounded motor
Answer  Explanation 

ANSWER: Series motor

Explanation:
No explanation is available for this question!


5)   Ward-Leonard control is basically a____________?

a. voltage control method
b. field divertor method
c. field control method
d. armature resistance control method
Answer  Explanation 

ANSWER: voltage control method

Explanation:
No explanation is available for this question!


6)   For constant torque drive which speed control method is preferred ?

a. Field control
b. Armature voltage control
c. Shunt armature control
d. Mechanical loading system
Answer  Explanation 

ANSWER: Armature voltage control

Explanation:
No explanation is available for this question!


7)   In Ward-Leonard control the lower limit of speed is imposed by________?

a. residual magnetism of the generator
b. core losses of motor
c. mechanical losses of motor and generator together
d. all of the above
Answer  Explanation 

ANSWER: residual magnetism of the generator

Explanation:
No explanation is available for this question!


8)   The main disadvantage of the Ward-Leonard control method is______________?

a. high initial cost
b. high maintenance cost
c. low efficiency at Hght loads
d. all of the above
Answer  Explanation 

ANSWER: all of the above

Explanation:
No explanation is available for this question!


9)   Regenerative method of braking is based on that___________?

a. back e.m.f. is less than the applied voltage
b. back e.m.f. is equal to the applied voltage
c. back e.m.f. of rotor is more than the applied voltage
d. none of the above
Answer  Explanation 

ANSWER: back e.m.f. is equal to the applied voltage

Explanation:
No explanation is available for this question!


10)   The hysteresis loss in a D.C. machine least depends on____________?

a. Frequency of magnetic reversals
b. Maximum value of flux density
c. Volume and grade of iron
d. Rate of flow of ventilating air
Answer  Explanation 

ANSWER: Rate of flow of ventilating air

Explanation:
No explanation is available for this question!


11)   In a D.C. generator all of the following could be the effects of iron losses except___________?

a. Loss of efficiency
b. Excessive heating of core
c. Increase in terminal voltage
d. Rise in temperature of ventilating air
Answer  Explanation 

ANSWER: Increase in terminal voltage

Explanation:
No explanation is available for this question!


12)   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 ?

a. hysteresis loss
b. field copper loss
c. armature copper loss
d. eddy current loss
Answer  Explanation 

ANSWER: armature copper loss

Explanation:
No explanation is available for this question!


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

a. Field copper loss
b. Windage loss
c. Armature copper loss
d. None of the above
Answer  Explanation 

ANSWER: Armature copper loss

Explanation:
No explanation is available for this question!


14)   Torque developed by a D.C. motor depends upon_____________?

a. magnetic field
b. active length of the conductor
c. current flow through the conductors
d. number of conductors
e. all above factors
Answer  Explanation 

ANSWER: all above factors

Explanation:
No explanation is available for this question!


15)   D.C. shunt motors are used for driving____________?

a. trains
b. cranes
c. hoists
d. machine tools
Answer  Explanation 

ANSWER: machine tools

Explanation:
No explanation is available for this question!


16)   In a manual shunt motor starter?

a. over load relay is connected in series and no volt relay in parallel with the load
b. over load relay is connected in parallel and no volt relay in series with the load
c. over load relay and no volt relay are both connected in series with the load
d. over load relay and no volt relay are both connected in parallel with the load
Answer  Explanation 

ANSWER: over load relay is connected in series and no volt relay in parallel with the load

Explanation:
No explanation is available for this question!


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

a. Providing laminations in armature core
b. Providing laminations in stator
c. Using non-magnetic material for frame
d. Using material of low hysteresis co-efficient for armature core material
Answer  Explanation 

ANSWER: Using material of low hysteresis co-efficient for armature core material

Explanation:
No explanation is available for this question!


18)   Which of the following loss in a D.C. generator is dissipated in the form of heat?

a. Mechanical loss
b. Core loss
c. Copper loss
d. All of the above
Answer  Explanation 

ANSWER: All of the above

Explanation:
No explanation is available for this question!


19)   Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?

a. Hysteresis losses
b. Eddy current losses
c. Copper losses
d. Windage losses
Answer  Explanation 

ANSWER: Eddy current losses

Explanation:
No explanation is available for this question!


20)   The total losses in a well designed D.C. generator of 10 kW will be nearly______________?

a. 100 W
b. 500 W
c. 1000 W
d. 1500 W
Answer  Explanation 

ANSWER: 500 W

Explanation:
No explanation is available for this question!