Quiz  /  Rectifiers Converters Electrical Engineering MCQ Interview Questions and Answers PDF

  • 1. 
    Which of the following are the applications of D.C. system ?

  • Battery charging work
  • Arc welding
  • Electrolytic and electro-chemical processes
  • Arc lamps for search lights
  • All of the above

  • 2. 
    Which of the following methods may be used to convert A.C. system to D.C. ?

  • Rectifiers
  • Motor converters
  • Motor-generator sets
  • Rotary converters
  • All of the above

  • 3. 
    In a single phase rotary converter the number of slip rings will be

  • two
  • three
  • four
  • six
  • none

  • 4. 
    A synchronous converter can be started

  • by means of a small auxiliary motor
  • from AC. side as induction motor
  • from D.C. side as D.C. motor
  • any of the above methods
  • none of the above methods

  • 5. 
    A rotary converter is a single machine with

  • one armature and one field
  • two armatures and one field
  • one armature and two fields
  • none of the above

  • 6. 
    A rotary converter combines the function of

  • an induction motor and a D.C. generator
  • a synchronous motor and a D.C. generator.
  • a D.C. series motor and a D.C. generator
  • none of the above

  • 7. 
    Which of the following is reversible in action ?

  • Motor generator set
  • Motor converter
  • Rotary converter
  • Any of the above
  • None of the above

  • 8. 
    Which of the following metals is generally manufactured by electrolysis process ?

  • Load
  • Aluminium
  • Copper
  • Zinc
  • None of the above

  • 9. 
    Normally, which of the following is used, when a large-scale conversion from AC. to D.C. power is required ?

  • Motor-generator set
  • Motor converter
  • Rotary converter
  • Mercury arc rectifier

  • 10. 
    A rotary converter in general construction and design, is more or less like

  • a transformer
  • an induction motor
  • an alternator
  • any D.C. machine

  • 11. 
    In which of the following appUcations, direct current is absolutely essential ?

  • Illumination
  • Electrolysis
  • Variable speed operation
  • Traction

  • 12. 
    Which of the following AC. motors is usually used in large motor-generator sets?

  • Synchronous motor
  • Squirrel cage induction motor
  • Slip ring induction motor
  • Any of the above

  • 13. 
    In which of the following equipment direct current is needed ?

  • Telephones
  • Relays
  • Time switches
  • All of the above

  • 14. 
    In a rotary converter I2R losses as compared to a D.C. generator of the same size will be

  • same
  • less
  • double
  • three times

  • 15. 
    In a mercury arc rectifier positive ions are attracted towards

  • anode
  • cathode
  • shell bottom
  • mercury pool

  • 16. 
    Mercury, in arc rectifiers, is chosen for cathode because

  • its ionization potential is relatively low
  • its atomic weight is quite high
  • its boiling point and specific heat are low
  • it remains in liquid state at ordi¬nary temperature
  • all of the above

  • 17. 
    The ionization potential of mercury is approximately

  • 5.4 V
  • 8.4 V
  • 10.4 V
  • 16.4 V

  • 18. 
    The potential drop in the arc, in a mercury arc rectifier, varies

  • 0.05 V to 0.2 V per cm length of the arc
  • 0.5 V to 1.5 V per cm length of the arc
  • 2 V to 3.5 V per cm length of the arc
  • none of the above

  • 19. 
    The voltage drop between the anode and cathode, of a mercury arc rectifier comprises of the following

  • anode drop and cathode drop
  • anode drop and arc drop
  • cathode drop and arc drop
  • anode drop, cathode drop and arc drop

  • 20. 
    Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of

  • 100 A at 100 V
  • 200 A at 200 V
  • 300 A at 300 V
  • 400 A at 400 V
  • 500 A at 500 V

  • 21. 
    The voltage drop at anode, in a mercury arc rectifier is due to

  • self restoring property of mercury
  • high ionization potential
  • energy spent in overcoming the electrostatic field
  • high temperature inside the rectifier

  • 22. 
    The internal efficiency of a mercury arc rectifier depends on

  • voltage only
  • current only
  • voltage and current
  • r.m.s. value of current
  • none of the above

  • 23. 
    If cathode and anode connections in a mercury arc rectifier are inter changed

  • the rectifier will not operate
  • internal losses will be reduced
  • both ion and electron streams will move in the same direction
  • the rectifier will operate at reduced efficiency

  • 24. 
    The cathdde voltage drop, in a mercury arc rectifier, is due to

  • expenditure of energy in ionization
  • surface resistance
  • expenditure of energy in overcoming the electrostatic field
  • expenditure of energy in liberating electrons from the mercury

  • 25. 
    To produce cathode spot in a mercury arc rectifier

  • anode is heated
  • tube is evacuated
  • an auxiliary electrode is used
  • low mercury vapour pressures are used

  • 26. 
    The advantage of mercury arc rectifier is that

  • it is light in weight and occupies small floor space
  • it has high efficiency
  • it has high overload capacity
  • it is comparatively noiseless
  • all of the above

  • 27. 
    In a mercury pool rectifier, the voltage drop across its electrodes

  • is directly proportional to load
  • is inversely proportional to load
  • varies exponentially with the load current
  • is almost independent of load current

  • 28. 
    In a three-phase mercury arc rectifiers each anode conducts for

  • one-third of a cycle
  • one-fourth of a cycle
  • one-half a cycle
  • two-third of a cycle

  • 29. 
    In a mercury arc rectifier characteristic blue luminosity is due to

  • colour of mercury
  • ionization
  • high temperature
  • electron streams

  • 30. 
    Which of the following mercury arc rectifier will deliver least undulating current?

  • Six-phase
  • Three-phase
  • Two-phase
  • Single-phase

  • 31. 
    In a glass bulb mercury arc rectifier the maximum current rating is restricted to

  • 2000 A
  • 1500 A
  • 1000 A
  • 500 A

  • 32. 
    In a mercury arc rectifier______ flow from anode to cathode

  • ions
  • electrons
  • ions and electrons
  • any of the above

  • 33. 
    On which of the following factors the number of phases for which a rectifier should be designed depend ?

  • The voltage regulation of the rec¬tifier should be low
  • In the output circuit there should be no harmonics
  • The power factor of the system should be high
  • The rectifier supply transformer should be utilized to the best ad-vantage
  • all of the above

  • 34. 
    A mercury arc rectifier possesses ________ regulation characteristics

  • straight line
  • curved line
  • exponential
  • none of the above

  • 35. 
    It is the_______of the transformer on which the magnitude of angle of overlap depends.

  • resistance
  • capacitance
  • leakage reactance
  • any of the above

  • 36. 
    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.

  • accelerates
  • decelerates
  • any of the above
  • none of the above

  • 37. 
    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

  • maximum grid voltage
  • critical grid voltage
  • any of the above
  • none of the above

  • 38. 
    In phase-shift control method the control is carried out by varying the of grid voltage.

  • magnitude
  • polarity
  • phase
  • any of the above
  • none of the above

  • 39. 
    The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?

  • They are mechanically strong
  • They do not require any voltage for filament heating
  • Both (a) and (b)
  • None of the above

  • 40. 
    Which of the following statement is incorrect ?

  • Copper oxide rectifier is a linear device
  • Copper oxide rectifier is not a perfect rectifier
  • Copper oxide rectifier has a low efficiency
  • Copper oxide rectifier finds use in control circuits
  • Copper oxide rectifier is not stable during early life

  • 41. 
    The efficiency of the copper oxide rectifier seldom exceeds

  • 90 to 95%
  • 85 to 90%
  • 80 to 85%
  • 65 to 75%

  • 42. 
    Copper oxide rectifier is usually designed not to operate above

  • 10°C
  • 20°C
  • 30°C
  • 45°C

  • 43. 
    Selenium rectifier can be operated at temperatures as high as

  • 25°C
  • 40°C
  • 60°C
  • 75°C

  • 44. 
    In selenium rectifiers efficiencies ranging from ______ to ______ percent are attainable

  • 25, 35
  • 40, 50
  • 60, 70
  • 75, 85

  • 45. 
    Ageing of a selenium rectifier may change the output voltage by

  • 5 to 10 per cent
  • 15 to 20 per cent
  • 25 to 30 per cent
  • none of the above

  • 46. 
    The applications of selenium rectifiers are usually limited to potential of

  • 10 V
  • 30 V
  • 60 V
  • 100 V
  • 200 V

  • 47. 
    Which of the following rectifiers have been used extensively in supplying direct current for electroplating ?

  • Copper oxide rectifiers
  • Selenium rectifiers
  • Mercury arc rectifiers
  • Mechanical rectifiers
  • None of the above

  • 48. 
    A commutating rectifier consists of commutator driven by

  • an induction motor
  • a synchronous motor
  • a D.C. series motor
  • a D.C. shunt motor

  • 49. 
    Which of the following rectifiers are primarily used for charging of low voltage batteries from AC. supply ?

  • Mechanical rectifiers
  • Copper oxide rectifiers
  • Selenium rectifiers
  • Electrolytic rectifiers
  • Mercury arc rectifiers

  • 50. 
    The efficiency of an electrolytic rectifier is nearly

  • 80%
  • 70%
  • 60%
  • 40%

  • 51. 
    The metal rectifiers, as compared to mercury arc rectifiers

  • operate on low temperatures
  • can operate on high voltages
  • can operate on heavy loads
  • give poor regulation
  • none of the above

  • 52. 
    In a mercury arc rectifier, the anode is usually made of

  • copper
  • aluminium
  • silver
  • graphite
  • tungsten

  • 53. 
    The ignited or auxiliary anode in mercury arc rectifier is made of

  • graphite
  • boron carbide
  • aluminium
  • copper
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