rectifiers and converters Mcqs
1. In a rotary converter I2R losses as compared to a D.C. generator of the same size will be___________?
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A. three times

B. less

C. double

D. same

2. In a mercury arc rectifier characteristic blue luminosity is due to_____________?
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A. electron streams

B. high temperature

C. colour of mercury

D. ionization
3. Selenium rectifier can be operated at temperatures as high as____________?
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A. 25C

B. 60C

C. 75C

D. 40C

4. In a mercury arc rectifier, the anode is usually made of_____________?
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A. copper

B. tungsten

C. aluminium

D. graphite

E. silver

5. A commutating rectifier consists of commutator driven by___________?
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A. a D.C. series motor

B. a synchronous motor

C. an induction motor

D. a D.C. shunt motor

6. A rotary converter in general construction and design, is more or less like___________?
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A. an alternator

B. any D.C. machine

C. a transformer

D. an induction motor

7. In which of the following appUcations, direct current is absolutely essential ?
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A. Variable speed operation

B. Electrolysis

C. Illumination

D. Traction

8. In a mercury arc rectifier________ flow from anode to cathode
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A. ions

B. any of the above

C. ions and electrons

D. electrons

9. The ionization potential of mercury is approximately_____________?
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A. 5.4 V

B. 10.4 V

C. 16.4 V

D. 8.4 V

10. In mercury arc rectifiers having grid, the arc can be struck between anode and cathode only when the grid attains a certain potential, this potential being known as______________?
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A. maximum grid voltage

B. critical grid voltage

C. none of the above

D. any of the above

11. The efficiency of the copper oxide rectifier seldom exceeds____________?
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A. 80 to 85%

B. 90 to 95%

C. 85 to 90%

D. 65 to 75%
12. To produce cathode spot in a mercury arc rectifier______________?
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A. low mercury vapour pressures are used

B. anode is heated

C. an auxiliary electrode is used

D. tube is evacuated

13. In a glass bulb mercury arc rectifier the maximum current rating is restricted to___________?
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A. 1500 A

B. 500 A

C. 2000 A

D. 1000 A

14. The applications of selenium rectifiers are usually limited to potential of_____________?
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A. 200 V

B. 10 V

C. 30 V

D. 100 V

E. 60 V

15. With a motor converter it is possible to obtain D.C. voltage only upto__________?
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A. 200-100 V

B. 10001200 V

C. 17002000 V

D. 600800 V

16. A rotary converter operates at a______________?
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A. high power factor

B. low power factor

C. none of the above

D. zero power factor

17. Which of the following AC. motors is usually used in large motor-generator sets?
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A. Squirrel cage induction motor

B. Any of the above

C. Slip ring induction motor

D. Synchronous motor
18. The efficiency of an electrolytic rectifier is nearly____________?
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A. 70%

B. 80%

C. 40%

D. 60%
19. Mercury, in arc rectifiers, is chosen for cathode because________________?
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A. all of the above

B. its ionization potential is relatively low

C. it remains in liquid state at ordinary temperature

D. its atomic weight is quite high

E. its boiling point and specific heat are low

20. A mercury arc rectifier possesses __________ regulation characteristics
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A. curved line

B. exponential

C. none of the above

D. straight line

21. In a mercury pool rectifier, the voltage drop across its electrodes___________?
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A. is almost independent of load current

B. varies exponentially with the load current

C. is directly proportional to load

D. is inversely proportional to load

22. In a grid control of mercury arc rectifiers when the grid is made positive relative to cathode, then it the electrons on their may to anode.
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A. decelerates

B. any of the above

C. none of the above

D. accelerates
23. Which of the following rectifiers are primarily used for charging of low voltage batteries from AC supply ?
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A. Selenium rectifiers

B. Copper oxide rectifiers

C. Electrolytic rectifiers

D. Mercury arc rectifiers

E. Mechanical rectifiers

24. It is the_________of the transformer on which the magnitude of angle of overlap depends?
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A. leakage reactance

B. resistance

C. capacitance

D. any of the above

25. Ageing of a selenium rectifier may change the output voltage by__________?
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A. 5 to 10 per cent

B. none of the above

C. 15 to 20 per cent

D. 25 to 30 per cent

26. The internal efficiency of a mercury arc rectifier depends on___________?
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A. voltage only

B. current only

C. none of the above

D. voltage and current

E. r.m.s. value of current

27. Which of the following is the loss within the mercury arc rectifier chamber ?
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A. Voltage drop at the cathode

B. Voltage drop at the anode

C. Voltage drop in arc

D. All of the above
28. If cathode and anode connections in a mercury arc rectifier are inter changed_____________?
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A. the rectifier will not operate

B. internal losses will be reduced

C. both ion and electron streams will move in the same direction

D. the rectifier will operate at reduced efficiency

29. In a single phase rotary converter the number of slip rings will be_____________?
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A. three

B. none

C. two

D. four

E. six

30. A rotary converter combines the function of____________?
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A. none of the above

B. a D.C. series motor and a D.C. generator

C. an induction motor and a D.C. generator

D. a synchronous motor and a D.C. generator
31. Which of the following rectifiers have been used extensively in supplying direct current for electroplating ?
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A. Copper oxide rectifiers

B. None of the above

C. Mercury arc rectifiers

D. Mechanical rectifiers

E. Selenium rectifiers
32. Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of _____________?
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A. 400 A at 400 V

B. 500 A at 500 V

C. 200 A at 200 V

D. 100 A at 100 V

E. 300 A at 300 V

33. In a three-phase mercury arc rectifiers each anode conducts for____________?
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A. one-half a cycle

B. one-fourth of a cycle

C. one-third of a cycle

D. two-third of a cycle

34. Normally, which of the following is used, when a large-scale conversion from AC. to D.C. power is required ?
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A. Mercury arc rectifier

B. Motor converter

C. Rotary converter

D. Motor-generator set

35. The cathdde voltage drop, in a mercury arc rectifier, is due to_____________?
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A. expenditure of energy in ionization

B. expenditure of energy in overcoming the electrostatic field

C. surface resistance

D. expenditure of energy in liberating electrons from the mercury
36. Which of the following are the applications of D.C. system ?
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A. Arc lamps for search lights

B. Arc welding

C. Electrolytic and electro-chemical processes

D. All of the above

E. Battery charging work

37. The advantage of mercury arc rectifier is that________________?
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A. it is comparatively noiseless

B. it is light in weight and occupies small floor space

C. it has high efficiency

D. it has high overload capacity

E. all of the above
38. In which of the following equipment direct current is needed ?
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A. Relays

B. All of the above

C. Telephones

D. Time switches

39. On which of the following factors the number of phases for which a rectifier should be designed depend ?
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A. In the output circuit there should be no harmonics

B. all of the above

C. The voltage regulation of the rectifier should be low

D. The power factor of the system should be high

E. The rectifier supply transformer should be utilized to the best ad-vantage

40. Which of the following statement is incorrect ?
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A. Copper oxide rectifier is not stable during early life

B. Copper oxide rectifier is not a perfect rectifier

C. Copper oxide rectifier finds use in control circuits

D. Copper oxide rectifier has a low efficiency

E. Copper oxide rectifier is a linear device
41. In a rotary converter armature currents are______________?
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A. a.c. only

B. d.c. only

C. partly a.c. and partly d.c.
42. When a rectifier is loaded which of the following voltage drops take place ?
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A. Arc voltage drop

B. All of the above

C. Voltage drop in resistance of transformer and smoothing chokes

D. Voltage drop in transformer reactance

43. In a mercury arc rectifier positive ions are attracted towards______________?
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A. mercury pool

B. shell bottom

C. anode

D. cathode
44. The voltage drop at anode, in a mercury arc rectifier is due to_____________?
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A. high ionization potential

B. self restoring property of mercury

C. energy spent in overcoming the electrostatic field

D. high temperature inside the rectifier

45. Which of the following methods may be used to convert A.C. system to D.C ?
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A. Motor-generator sets

B. Rotary converters

C. All of the above

D. Rectifiers

E. Motor converters

46. Which of the following is reversible in action ?
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A. Rotary converter

B. Any of the above

C. None of the above

D. Motor generator set

E. Motor converter

47. A synchronous converter can be started______________?
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A. from AC. side as induction motor

B. from D.C. side as D.C. motor

C. by means of a small auxiliary motor

D. any of the above methods

E. none of the above methods

48. A rotary converter is a single machine with______________?
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A. one armature and one field

B. two armatures and one field

C. one armature and two fields

D. none of the above

49. In phase-shift control method the control is carried out by varying the of grid voltage
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A. none of the above

B. phase

C. any of the above

D. magnitude

E. polarity

50. The potential drop in the arc, in a mercury arc rectifier, varies_____________?
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A. 0.05 V to 0.2 V per cm length of the arc

B. 2 V to 3.5 V per cm length of the arc

C. none of the above

D. 0.5 V to 1.5 V per cm length of the arc