1. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
(o) regenerative
(b) plugging
(c) dynamic braking
(d) none of the above
(e) any of the above
Ans: b
2. Which of the following motors one will choose to drive the rotary compressor ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Universal motor
(d) Synchronous motor
Ans: d
3. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
(a) increase
(b) decrease
(c) remain same
(d) become zero
Ans: a
4. 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
Ans: d
5. 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
Ans: c
6. 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
Ans: d
7. Which motor should not be started on no-load ?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor.
Ans: a
8. Ward-Leonard control is basically a
(a) voltage control method
(b) field divertor method
(c) field control method
(d) armature resistance control method
Ans: a
9. 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
Ans: b
10. 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 gen¬erator together
(d) all of the above
Ans: a
11. 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
Ans: d
12. 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
Ans: b
13. 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
Ans: d
14. 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
Ans: c
15. 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
Ans: c
16. 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
Ans: c
17. 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) radius of armature
(f) all above factors
Ans: f
18. D.C. shunt motors are used for driving
(a) trains
(b) cranes
(c) hoists
(d) machine tools
Ans: d
19. In a manual shunt motor starter
(a) over load relay is connected in series and no volt relay in parallel with the load
(6) over load relay is connected in paral¬lel 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
Ans: a
20. 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
Ans: d
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