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BSNL TTA (Junior Engineer - JE) Practice Paper on "Electricity"

Current Electricity

1. The S.I. unit of power is
a. Henry
b. Coulomb
c. Watt
d. Watt-hour
Answer: C

2. Electric pressure is also called
a. resistance
b. power
c. voltage
d. energy
Answer: C

3. The substances which have a large number of free electrons and offer a low resistance are called
a. insulators
b. inductors
c. semi-conductors
d. conductors
Answer: D

4. Out of the following which is not a poor conductor ?
a. Cast iron
b. Copper
c. Carbon
d. Tungsten
Answer: B

5. Out of the following which is an insulating material ?
a. Copper
b. Gold
c. Silver
d. Paper
Answer: D

6. The property of a conductor due to which it passes current is called
a. resistance
b. reluctance
c. conductance
d. inductance
Answer: C

7. Conductance is reciprocal of
a. resistance
b. inductance
c. reluctance
d. capacitance
Answer: A

8. The resistance of a conductor varies inversely as
a. length
b. area of cross-section
c. temperature
d. resistivity
Answer: B

9. With rise in temperature the resistance of pure metals
a. increases
b. decreases
c. first increases and then decreases
d. remains constant
Answer: A

10. With rise in temperature the resistance of semi-conductors
a. decreases
b. increases
c. first increases and then decreases
d. remains constant
Answer: A

11. The resistance of a copper wire 200 m long is 21Ω. If its thickness (diameter) is 0.44 mm, its specific resistance is
a. 1.2 x 108 Ω-m
b. 1.4 x 108 Ω-m
c. 1.6 x 108 Ω-m
d. 1.8 x 108 Ω-m
Answer: C

12. Three resistances of 10 ohms, 15 ohms and 30 ohms are connected in parallel.
The total resistance of the combination is
a. 5 ohms
b. 10 ohms
c. 15 ohms
d. 55 ohms
Answer: A

13. An instrument which detects electric current is known as
a. voltmeter
b. rheostat
c. wattmeter
d. galvanometer
Answer: D

14. In a circuit a 33 Ω resistor carries a current of 2 A. The voltage across the
resistor is
a. 33 V
b. 66 v
c. 80 V
d. 132 V
Answer: B

15. A light bulb draws 300 mA when the voltage across it is 240 V. The resistance of the light bulb is
a. 400 Ω
b. 600 Ω
c. 800 Ω
d. 1000 Ω
Answer: C

16. The resistance of a parallel circuit consisting of two branches is 12 ohms. If the resistance of one branch is 18 ohms, what is the resistance of the other?
a. 18 Ω
b. 36 Ω
c. 48 Ω
d. 64 Ω
Answer: B

17. Four wires of same material, the same cross-sectional area and the same length when connected in parallel give a resistance of 0.25 Ω. If the same four wires are connected is series the effective resistance will be
a. 1 Ω
b. 2 Ω
c. 3 Ω
d. 4 Ω
Answer: D

18. A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is
a. 6.4 A, 6.9 A
b. 6.4 A, 9.6 A
c. 4.6 A, 6.9 A
d. 4.6 A, 9.6 A
Answer: B

19. Current velocity through a copper conductor is
a. the same as propagation velocity of electric energy
b. independent of current strength
c. of the order of a few 108 m/s
d. nearly 3 x 108 m/s
Answer: C

20. Which of the following material has nearly zero temperature co-efficient of resistance?
a. Manganin
b. Porcelain
c. Carbon
d. Copper
Answer: A

21. You have to replace 1500 Ω resistor in radio. You have no 1500 Ω resistor but have several 1000 Ω ones which you would connect
a. two in parallel
b. two in parallel and one in series
c. three in parallel
d. three in series
Answer: B

22. Two resistors are said to be connected in series when
a. same current passes in turn through both
b. both carry the same value of current
c. total current equals the sum of branch currents
d. sum of IR drops equals the applied e.m.f.
Answer: A

23. Which of the following statement is true both for a series and a parallel D.C. circuit?
a. Elements have individual currents
b. Currents are additive
c. Voltages are additive
d. Power are additive
Answer: D

24. Which of the following materials has a negative temperature co-efficient of resistance?
a. Copper
b. Aluminum
c. Carbon
d. Brass
Answer: C

25. Ohm's law is not applicable to
a. vacuum tubes
b. carbon resistors
c. high voltage circuits
d. circuits with low current densities
Answer: A

26. Which is the best conductor of electricity?
a. Iron
b. Silver
c. Copper
d. Carbon
Answer: B

27. For which of the following 'ampere second' could be the unit?
a. Reluctance
b. Charge
c. Power
d. Energy
Answer: B

28. All of the following are equivalent to watt except
a. amperes x ohm
b. joules/sec.
c. amperes x volts
d. amperes/volt
Answer: D

29. A resistance having rating 10 ohms, 10W is likely to be a
a. metallic resistor
b. carbon resistor
c. wire wound resistor
d. variable resistor
Answer: C

30. Which one of the following does not have negative temperature co-efficient?
a. Aluminium
b. Paper
c. Rubber
d. Mica
Answer: A

31. Varistors are
a. insulators
b. non-linear resistors
c. carbon resistors
d. resistors with zero temperature coefficient
Answer: B

32. Insulating materials have the function of
a. preventing a short circuit between conducting wires
b. preventing an open circuit between the voltage source and the load
c. conducting very large currents
d. storing very high currents
Answer: B

33. The rating of a fuse wire is always expressed in
a. ampere-hours
b. ampere-volts
c. kWh
d. amperes
Answer: D

34. The minimum charge on an ion is
a. equal to the atomic number of the atom
b. equal to the charge of an electron
c. equal to the charge of the number of electrons in an atom
d. zero
Answer: B

35. In a series circuit with unequal resistances
a. the highest resistance has the most of the current through it
b. the lowest resistance has the highest voltage drop
c. the lowest resistance has the highest current
d. the highest resistance has the highest voltage drop
Answer: D

36. The filament of an electric bulb is made of
a. carbon
b. aluminium
c. tungsten
d. nickel
Answer: C

37. A 3 Ω resistor having 2 A current will dissipate the power of
a. 2 watts
b. 4 watts
c. 6 watts
d. 8 watts
Answer: C

38. Which of the following statement is true?
a. A galvanometer with low resistance in parallel is a voltmeter
b. A galvanometer with high resistance in parallel is a voltmeter
c. A galvanometer with low resistance in series is an ammeter
d. A galvanometer with high resistance in series is an ammeter
Answer: C

39. The resistance of a few metres of wire conductor in closed electrical circuit is
a. practically zero
b. low
c. high
d. very high
Answer: A

40. If a parallel circuit is opened in the main line, the current
a. increases in the branch of the lowest resistance
b. increases in each branch
c. is zero in all branches
d. is zero in the highest resistive branch
Answer: C

41. If a wire conductor of 0.2 ohm resistance is doubled in length, its resistance becomes
a. 0.4 ohm
b. 0.6 ohm
c. 0.8 ohm
d. 1.0 ohm
Answer: A

42. Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns then
a. there will be heavy current in the main line
b. rest of the two bulbs will not light
c. all three bulbs will light
d. the other two bulbs will light
Answer: D

43. The four bulbs of 40 W each are connected in series with a battery across them, which of the following statement is true ?
a. The current through each bulb in same
b. The voltage across each bulb is not same
c. The power dissipation in each bulb is not same
d. None of the above
Answer: A

44. Two resistances Rl and Ri are connected in series across the voltage source where R1>Ri. The largest drop will be across
a. R1
b. Ri
c. either Rl or Ri
d. none of them
Answer: A

45. What will be energy used by the battery if the battery has to drive 6.28 x 1018 electrons with potential difference of 20 V across the terminal ?
a. 5 joules
b. 10 joules
c. 15 joules
d. 20 joules
Answer: D

46. A closed switch has a resistance of
a. zero
b. about 50 ohms
c. about 500 ohms
d. infinity
Answer: A

47. The hot resistance of the bulb's filament is higher than its cold resistance because the temperature co-efficient of the filament is
a. zero
b. negative
c. positive
d. about 2 ohms per degree
Answer: C

48. Heat in a conductor is produced on the passage of electric current due to
a. reactance
b. capacitance
c. impedance
d. resistance

49. The insulation on a current carrying conductor is provided
a. to prevent leakage of current
b. to prevent shock
c. both of above factors
d. none of above factors
Answer: C

50. The thickness of insulation provided on the conductor depends on
a. the magnitude of voltage on the conductor
b. the magnitude of current flowing through it
c. both a. and b.
d. none of the above
Answer: A

51. Which of the following quantities remain the same in all parts of a series circuit?
a. Voltage
b. Current
c. Power
d. Resistance
Answer: B

52. A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the heater output will
a. decrease
b. increase
c. remain same
d. heater will burn out
Answer: B

53. In an electric kettle, water boils in 10m minutes. It is required to boil the water in 15 minutes, using same supply mains
a. length of heating element should be decreased
b. length of heating element should be increased
c. length of heating element has no effect on heating if water
d. none of the above
Answer: A

54. An electric filament bulb can be worked from
a. D.C. supply only
b. A.C. supply only
c. Battery supply only
d. All above
Answer: D

55. Resistance of a tungsten lamp as applied voltage increases
a. decreases
b. increases
c. remains same
d. none of the above
Answer: B

56. Electric current passing through the circuit produces
a. magnetic effect
b. luminous effect
c. thermal effect
d. chemical effect
e. all above effects
Answer: C

57. Resistance of a material always decreases if
a. temperature of material is decreased
b. temperature of material is increased
c. number of free electrons available become more
d. none of the above is correct
Answer: C

58. If the efficiency of a machine is to be high, what should be low ?
a. Input power
b. Losses
c. True component of power
d. kWh consumed
e. Ratio of output to input
Answer: B

59. When electric current passes through a metallic conductor, its temperature rises. This is due to
a. collisions between conduction electrons and atoms
b. the release of conduction electrons from parent atoms
c. mutual collisions between metal atoms
d. mutual collisions between conducting electrons
Answer: A

60. Two bulbs of 500 W and 200 W rated at 250 V will have resistance ratio as
a. 4 : 25
b. 25 : 4
c. 2 : 5
d. 5 : 2
Answer: C

61. A glass rod when rubbed with silk cloth is charged because
a. it takes in proton
b. its atoms are removed
c. it gives away electrons
d. it gives away positive charge
Answer: C

62. Whether circuit may be AC. or D.C. one, following is most effective in reducing the magnitude of the current.
a. Reactor
b. Capacitor
c. Inductor
d. Resistor
Answer: D

63. It becomes more difficult to remove
a. any electron from the orbit
b. first electron from the orbit
c. second electron from the orbit
d. third electron from the orbit
Answer: D

64. When one leg of parallel circuit is opened out the total current will
a. reduce
b. increase
c. decrease
d. become zero
Answer: C

65. In a lamp load when more than one lamp are switched on the total resistance of the load
a. increases
b. decreases
c. remains same
d. none of the above
Answer: B

66. Two lamps 100 W and 40 W are connected in series across 230 V (alternating).
Which of the following statement is correct ?
a. 100 W lamp will glow brighter
b. 40 W lamp will glow brighter
c. Both lamps will glow equally bright
d. 40 W lamp will fuse
Answer: B

67. Resistance of 220 V, 100 W lamp will be
a. 4.84 Ω
b. 48.4 Ω
c. 484 Ω
d. 4840 Ω
Answer: C

68. In the case of direct current
a. magnitude and direction of current remains constant
b. magnitude and direction of current changes with time
c. magnitude of current changes with time
d. magnitude of current remains constant
Answer: A

69. When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is
a. A.C.
b. D.C.
c. any of above two
d. none of the above
Answer: B

70. Resistance of carbon filament lamp as the applied voltage increases.
a. increases
b. decreases
c. remains same
d. none of the above
Answer: B

71. Bulbs in street lighting are all connected in
a. parallel
b. series
c. series-parallel
d. end-to-end
Answer: A

72. For testing appliances, the wattage of test lamp should be
a. very low
b. low
c. high
d. any value
Answer: C

73. Switching of a lamp in house produces noise in the radio. This is because switching operation produces
a. arcs across separating contacts
b. mechanical noise of high intensity
c. both mechanical noise and arc between contacts
d. none of the above
Answer: A

74. Sparking occurs when a load is switched off because the circuit has high
a. resistance
b. inductance
c. capacitance
d. impedance
Answer: B

75. Copper wire of certain length and resistance is drawn out to three times its length without change in volume, the new resistance of wire becomes
a. 1/9 times
b. 3 times
c. 9 times
d. unchanged
Answer: C

76. When resistance element of a heater fuses and then we reconnect it after removing a portion of it, the power of the heater will
a. decrease
b. increase
c. remain constant
d. none of the above
Answer: B

77. A field of force can exist only between
a. two molecules
b. two ions
c. two atoms
d. two metal particles
Answer: B

78. A substance whose molecules consist of dissimilar atoms is called
a. semiconductor
b. super-conductor
c. compound
d. insulator
Answer: C

79. International ohm is defined in terms of the resistance of
a. a column of mercury
b. a cube of carbon
c. a cube of copper
d. the unit length of wire
Answer: A

80. Three identical resistors are first connected in parallel and then in series.
The resultant resistance of the first combination to the second will be
a. 9 times
b. 1/9 times
c. 1/3 times
d. 3 times
Answer: B

91. Which method can be used for absolute measurement of resistance?
a. Lorentz method
b. Releigh method
c. Ohm's law method
d. Wheatstone bridge method
Answer: D

92. Three 6 ohm resistors are connected to form a triangle. What is the resistance between any two corners?
a. 3/2 Ω
b. 6 Ω
c. 4 Q
d. 8/3 Q
Answer: C

93. Ohm's law is not applicable to
a. semi-conductors
b. D.C. circuits
c. small resistors
d. high currents
Answer: A

94. Two copper conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 40 ohms the resistance of other conductor will be
a. 160 ohms
b. 80 ohms
c. 20 ohms
d. 10 ohms
Answer: D

95. A nichrome wire used as a heater coil has the resistance of 2 ohm. For a heater of 1 kW at 200 V, the length of wire required will be
a. 80 m
b. 60 m
c. 40 m
d. 20 m
Answer: A

96. Temperature co-efficient of resistance is expressed in terms of
a. ohms/°C
b. mhos/ohm°C
c. ohms/ohm°C
d. mhos/°C
Answer: C

97. Which of the following materials has the least resistivity?
a. Zinc
b. Lead
c. Mercury
d. Copper

98. When current flows through heater coil it glows but supply wiring does not glow because
a. current through supply line flows at slower speed
b. supply wiring is covered with insulation layer
c. resistance of heater coil is more than the supply wires
d. supply wires are made of superior material
Answer: C

99. The condition for the validity under Ohm's law is that
a. resistance must be uniform
b. current should be proportional to the size of the resistance
c. resistance must be wire wound type
d. temperature at positive end should be more than the temperature at negative end
Answer: A

100. Which of the following statement is correct ?
a. A semi-conductor is a material whose conductivity is same as between that of a conductor and an insulator
b. A semi-conductor is a material which has conductivity having average value of conductivity of metal and insulator
c. A semi-conductor is one which conducts only half of the applied voltage
d. A semi-conductor is a material made of alternate layers of conducting material and insulator
Answer: A

101. A rheostat differs from potentiometer in the respect that it
a. has lower wattage rating
b. has higher wattage rating
c. has large number of turns
d. offers large number of tappings
Answer: B

102. The weight of an aluminium conductor as compared to a copper conductor of identical cross-section, for the same electrical resistance, is
a. 50%
b. 60%
c. 100%
d. 150%
Answer: A

103. An open resistor, when checked with an ohm-meter reads
a. zero
b. infinite
c. high but within tolerance
d. low but not zero
Answer: B

104. are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.
a. Varistors
b. Thermistor
c. Semiconductors
d. Variable resistors
Answer: C

105. All good conductors have high
a. conductance
b. resistance
c. reluctance
d. thermal conductivity
Answer: A

106. Voltage dependent resistors are usually made from
a. charcoal
b. silicon carbide
c. nichrome
d. graphite
Answer: C

107. Voltage dependent resistors are used
a. for inductive circuits
b. to supress surges
c. as heating elements
d. as current stabilizers
Answer: B

108. The ratio of mass of proton to that of electron is nearly
a. 1840
b. 1840
c. 30
d. 4
Answer: A

109. The number of electrons in the outer most orbit of carbon atom is
a. 3
b. 4
c. 6
d. 7
Answer: B

110. With three resistances connected in parallel, if each dissipates 20 W, the total power supplied by the voltage source equals
a. 10 W
b. 20 W
c. 40 W
d. 60 W
Answer: D

111. A thermistor has
a. positive temperature coefficient
b. negative temperature coefficient
c. zero temperature coefficient
d. variable temperature coefficient
Answer: C

112. If I, R and t are the current, resistance and time respectively, then according to Joule's law heat produced will be proportional to
a. I2Rt
b. I2Rf
c. I2R2t
d. I2R2t2
Answer: A

113. Nichrome wire is an alloy of
a. lead and zinc
b. chromium and vanadium
c. nickel and chromium
d. copper and silver
Answer: C

114. When a voltage of one volt is applied, a circuit allows one microampere current to flow through it. The conductance of the circuit is
a. 1 micro mho
b. 106 mho
c. 1 milli-mho
d. none of the above
Answer: A

115. Which of the following can have negative temperature coefficient?
a. Compounds of silver
b. Liquid metals
c. Metallic alloys
d. Electrolytes
Answer: D

116. Conductance : mho ::
a. resistance : ohm
b. capacitance : henry
c. inductance : farad
d. lumen : steradian
Answer: A

117. 1 angstrom is equal to
a. 10-8 mm
b. 106 cm
c. 10-10 m
d. 10-14 m

Answer: C
118. One newton metre is same as
a. one watt
b. one joule
c. five joules
d. one joule second
Answer: B

BSNL TTA (Junior Engineer - JE) Practice Paper on "Rectifiers and Converters"

Rectifiers and Converters

1. Which of the following are the applications of D.C. system ?
(a) Battery charging work
(b) Arc welding
(c) Electrolytic and electro-chemical processes
(d) Arc lamps for search lights
(e) All of the above
Answer: E

2. Which of the following methods may be used to convert A.C. system to D.C. ?
(a) Rectifiers
(b) Motor converters
(c) Motor-generator sets
(d) Rotary converters
(e) All of the above
Answer: E

3. In a single phase rotary converter the number of slip rings will be
(a) two
(b) three
(c) four
(d) six
(e) none
Answer: A

4. A synchronous converter can be started
(a) by means of a small auxiliary motor
(b) from AC. side as induction motor
(c) from D.C. side as D.C. motor
(d) any of the above methods
(e) none of the above methods
Answer: D

5. A rotary converter is a single machine with
(a) one armature and one field
(b) two armatures and one field
(c) one armature and two fields
(d) none of the above
Answer: A

6. A rotary converter combines the function of
(a) an induction motor and a D.C. generator
(b) a synchronous motor and a D.C. generator.
(c) a D.C. series motor and a D.C. generator
(d) none of the above
Answer: B

7. Which of the following is reversible in action ?
(a) Motor generator set
(b) Motor converter
(c) Rotary converter
(d) Any of the above
(e) None of the above
Answer: C

8. Which of the following metals is generally manufactured by electrolysis process ?
(a) Load
(b) Aluminium
(c) Copper
(d) Zinc
(e) None of the above
Answer: B

9. With a motor converter it is possible to obtain D.C. voltage only upto
(a) 200-100 V
(6) 600—800 V
(c) 1000—1200 V
(d) 1700—2000 V
Answer: D

10. Normally, which of the following is used, when a large-scale conversion from AC. to D.C. power is required ?
(a) Motor-generator set
(b) Motor converter
(c) Rotary converter
(d) Mercury arc rectifier
Answer: D

11. A rotary converter in general construction and design, is more or less like
(a) a transformer
(b) an induction motor
(c) an alternator
(d) any D.C. machine
Answer: D

12. A rotary converter operates at a
(a) low power factor
(6) high power factor
(c) zero power factor
(d) none of the above
Answer: B

13. In which of the following appUcations, direct current is absolutely essential ?
(a) Illumination
(b) Electrolysis
(c) Variable speed operation
(d) Traction
Answer: B

14. Which of the following AC. motors is usually used in large motor-generator sets?
(a) Synchronous motor
(b) Squirrel cage induction motor
(c) Slip ring induction motor
(d) Any of the above
Answer: A

15. In a rotary converter armature currents are
(a) d.c. only
(b) a.c. only
(c) partly a.c. and partly d.c.
Answer: C

16. In which of the following equipment direct current is needed ?
(a) Telephones
(b) Relays
(c) Time switches
(d) All of the above
Answer: D

17. In a rotary converter I2R losses as compared to a D.C. generator of the same size will be
(a) same
(b) less
(c) double
(d) three times
Answer: B

18. In a mercury arc rectifier positive ions are attracted towards
(a) anode
(b) cathode
(c) shell bottom
(d) mercury pool
Answer: B

19. Mercury, in arc rectifiers, is chosen for cathode because
(a) its ionization potential is relatively low
(b) its atomic weight is quite high
(c) its boiling point and specific heat are low
(d) it remains in liquid state at ordi¬nary temperature
(e) all of the above
Answer: E

20. The ionization potential of mercury is approximately
(a) 5.4 V
(b) 8.4 V
(c) 10.4 V
(d) 16.4 V
Answer: C

21. The potential drop in the arc, in a mercury arc rectifier, varies
(a) 0.05 V to 0.2 V per cm length of the arc
(b) 0.5 V to 1.5 V per cm length of the arc
(c) 2 V to 3.5 V per cm length of the arc
(d) none of the above
Answer: D

22. The voltage drop between the anode and cathode, of a mercury arc rectifier comprises of the following
(a) anode drop and cathode drop
(b) anode drop and arc drop
(c) cathode drop and arc drop
(d) anode drop, cathode drop and arc drop
Answer: D

23. Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of
(a) 100 A at 100 V
(b) 200 A at 200 V
(c) 300 A at 300 V
(d) 400 A at 400 V
(e) 500 A at 500 V
Answer: E

24. The voltage drop at anode, in a mercury arc rectifier is due to
(a) self restoring property of mercury
(b) high ionization potential
(c) energy spent in overcoming the electrostatic field
(d) high temperature inside the rectifier
Answer: C

25. The internal efficiency of a mercury arc rectifier depends on
(a) voltage only
(b) current only
(c) voltage and current
(d) r.m.s. value of current
(e) none of the above
Answer: A

26. If cathode and anode connections in a mercury arc rectifier are inter changed
(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
Answer: A

27. The cathdde voltage drop, in a mercury arc rectifier, is due to
(a) expenditure of energy in ionization
(b) surface resistance
(c) expenditure of energy in overcoming the electrostatic field
(d) expenditure of energy in liberating electrons from the mercury
Answer: D

28. To produce cathode spot in a mercury arc rectifier
(a) anode is heated
(b) tube is evacuated
(c) an auxiliary electrode is used
(d) low mercury vapour pressures are used
Answer: C

29. The advantage of mercury arc rectifier is that
(a) it is light in weight and occupies small floor space
(b) it has high efficiency
(c) it has high overload capacity
(d) it is comparatively noiseless
(e) all of the above
Answer: E

30. In a mercury pool rectifier, the voltage drop across its electrodes
(a) is directly proportional to load
(b) is inversely proportional to load
(c) varies exponentially with the load current
(d) is almost independent of load current
Answer: D

31. In a three-phase mercury arc rectifiers each anode conducts for
(a) one-third of a cycle
(b) one-fourth of a cycle
(c) one-half a cycle
(d) two-third of a cycle
Answer: A

32. In a mercury arc rectifier characteristic blue luminosity is due to
(a) colour of mercury
(b) ionization
(c) high temperature
(d) electron streams
Answer: B

33. Which of the following mercury arc rectifier will deliver least undulating current?
(a) Six-phase
(b) Three-phase
(c) Two-phase
(d) Single-phase
Answer: A

34. In a glass bulb mercury arc rectifier the maximum current rating is restricted to
(a) 2000 A
(b) 1500 A
(c) 1000 A
(d) 500 A
Answer: D

35. In a mercury arc rectifier______ flow from anode to cathode
(a) ions
(b) electrons
(c) ions and electrons
(d) any of the above
Answer: A

36. When a rectifier is loaded which of the following voltage drops take place ?
(a) Voltage drop in transformer reactance
(6) Voltage drop in resistance of transformer and smoothing chokes
(c) Arc voltage drop
(d) All of the above
Answer: D

37. On which of the following factors the number of phases for which a rectifier should be designed depend ?
(a) The voltage regulation of the rec¬tifier should be low
(b) In the output circuit there should be no harmonics
(c) The power factor of the system should be high
(d) The rectifier supply transformer should be utilized to the best ad-vantage
(e) all of the above
Answer: E

38. A mercury arc rectifier possesses ________ regulation characteristics
(a) straight line
(b) curved line
(c) exponential
(d) none of the above
Answer: D

39. It is the_______of the transformer on which the magnitude of angle of overlap depends.
(a) resistance
(b) capacitance
(c) leakage reactance
(d) any of the above
Answer: C

41. 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.
(a) accelerates
(b) decelerates
(c) any of the above
(d) none of the above
Answer: A

42. 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
(a) maximum grid voltage
(b) critical grid voltage
(c) any of the above
(d) none of the above
Answer: B

43. In phase-shift control method the control is carried out by varying the of grid voltage.
(a) magnitude
(b) polarity
(c) phase
(d) any of the above
(e) none of the above
Answer: C

44. In a phase-shift control method, the phase shift between anode and grid voltages can be achieved by means of
(a) shunt motor
(6) synchronous motor
(c) induction regulator
(d) synchronous generator
Answer: C

45. The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?
(a) They are mechanically strong
(b) They do not require any voltage for filament heating
(c) Both (a) and (b)
(d) None of the above
Answer: C

46. Which of the following statement is incorrect ?
(a) Copper oxide rectifier is a linear device
(b) Copper oxide rectifier is not a perfect rectifier
(c) Copper oxide rectifier has a low efficiency
(d) Copper oxide rectifier finds use in control circuits
(e) Copper oxide rectifier is not stable during early life
Answer: A

47. The efficiency of the copper oxide rectifier seldom exceeds
(a) 90 to 95%
(b) 85 to 90%
(c) 80 to 85%
(d) 65 to 75%
Answer: D

48. Copper oxide rectifier is usually designed not to operate above
(a) 10°C
(b) 20°C
(c) 30°C
(d) 45°C
Answer: D

49. Selenium rectifier can be operated at temperatures as high as
(a) 25°C
(b) 40°C
(c) 60°C
(d) 75°C
Answer: D

50. In selenium rectifiers efficiencies ranging from ______ to ______ percent are attainable
(a) 25, 35
(b) 40, 50
(c) 60, 70
(d) 75, 85
Answer: D

51. Ageing of a selenium rectifier may change the output voltage by
(a) 5 to 10 per cent
(b) 15 to 20 per cent
(c) 25 to 30 per cent
(d) none of the above
Answer: A

52. The applications of selenium rectifiers are usually limited to potential of
(a) 10 V
(b) 30 V
(c) 60 V
(d) 100 V
(e) 200 V
Answer: D

53. Which of the following rectifiers have been used extensively in supplying direct current for electroplating ?
(a) Copper oxide rectifiers
(b) Selenium rectifiers
(c) Mercury arc rectifiers
(d) Mechanical rectifiers
(e) None of the above
Answer: B

54. A commutating rectifier consists of commutator driven by
(a) an induction motor
(b) a synchronous motor
(c) a D.C. series motor
(d) a D.C. shunt motor
Answer: B

55. Which of the following rectifiers are primarily used for charging of low voltage batteries from AC. supply ?
(a) Mechanical rectifiers
(b) Copper oxide rectifiers
(c) Selenium rectifiers
(d) Electrolytic rectifiers
(e) Mercury arc rectifiers
Answer: D

56. The efficiency of an electrolytic rectifier is nearly
(a) 80%
(b) 70%
(c) 60%
(d) 40%
Answer: C

57. Which of the following is the loss within the mercury arc rectifier chamber ?
(a) Voltage drop in arc
(6) Voltage drop at the anode
(c) Voltage drop at the cathode
(d) All of the above
Answer: D

58. The metal rectifiers, as compared to mercury arc rectifiers
(a) operate on low temperatures
(b) can operate on high voltages
(c) can operate on heavy loads
(d) give poor regulation
(e) none of the above
Answer: A

59. In a mercury arc rectifier, the anode is usually made of
(a) copper
(b) aluminium
(c) silver
(d) graphite
(e) tungsten
Answer: D

60. The ignited or auxiliary anode in mercury arc rectifier is made of
(a) graphite
(b) boron carbide
(c) aluminum
(d) copper
Answer: B

BSNL TTA Practice Paper on Electrostatics (Junior Engineer - JE)

Electrostatics - Electrical Multiple Choice Questions with Answers

1. The force between two charges is 120 N. If the distance between the charges is doubled, the force will be
(a) 60 N
(b) 30 N
(c) 40 N
(d) 15 N
Answer: B

2. The electric field intensity at a point situated 4 metres from a point charge is 200 N/C. If the distance is reduced to 2 metres, the field intensity will be
(a) 400 N/C
(b) 600 N/C
(c) 800 N/C
(d) 1200 N/C
Answer: C

3. The lines of force due to charged particles are
(a) always straight
(b) always curved
(c) sometimes curved
(d) none of the above
Answer: B