EEE MCQ (D.C. Generators )

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D.C. Generators - Electrical engineering multiple choice questions and answers for competitive exams

1. Laminations of core are generally made of 
(a)     case iron
(b)     carbon
(c) silicon steel
(d) stainless steel

Ans: c

2. Which of the following could be lamina-proximately the thickness of lamina-tions of a D.C. machine ?
(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 m
(d) 5 m

Ans: c

3. The armature of D.C. generator is laminated to 
(a)     reduce the bulk
(b)     provide the bulk
(c) insulate the core
(d) reduce eddy current loss

Ans: d

4. The resistance of armature winding depends on
(a)     length of conductor
(b)     cross-sectional area of the conductor
(c) number of conductors
(d) all of the above

Ans: d

5. The field coils of D.C. generator are usually made of
(a) mica
(b) copper
(c) cast iron
(d) carbon

Ans: b

6. The commutator segments are connected to the armature conductors by means of
(a) copper lugs    
(b) resistance wires
(c) insulation pads
(d) brazing

Ans: a

7. In a commutator
(a)  copper is harder than mica
(b)  mica and copper are equally hard
(c) mica is harder than copper
(d) none of the above

Ans: c

8. In D.C. generators the pole shoes are fastened to the pole core by
(a) rivets
(b) counter sunk screws
(c) brazing
(d) welding

Ans: b

9. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of
(a) motion of conductor
(b) lines of force
(c) either of the above
(d) none of the above

Ans: b

10. Fleming's right-hand rule regarding direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow and resultant force
(b) magnetic flux, direction of motion and the direction of e.m.f. induced
(c) magnetic field strength, induced voltage and current
(d) magnetic flux, direction of force and direction of motion of conductor

Ans: b

11. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards
(a) direction of induced e.m.f.
(b) direction of flux
(c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
(d) direction of motion of conductor, if forefinger points along the lines of flux

Ans: d

12. The bearings used to support the rotor shafts are generally
(a) ball bearings  
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings

Ans: a

13. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking
(b) rough commutator surface
(c) imperfect contact
(d) any of the above

Ans: d

14. In lap winding, the number of brushes is always
(a) double the number of poles
(b) same as the number of poles
(c) half the number of poles
(d) two

Ans: b

15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?
(a) Lap winding  
(b) Wave winding
(c) Either of (a) and (b) above
(d) Depends on other features of design

Ans: b

16. In a four-pole D.C. machine
(a) all the four poles are north poles
(b) alternate poles are north and south
(c) all the four poles are south poles
(d) two north poles follow two south poles

Ans: b

17. Copper brushes in D.C. machine are used
(a) where low voltage and high currents are involved
(b) where high voltage and small cur-rents are involved
(c)  in both of the above cases
(d)  in none of the above cases

Ans: a

18. A separately excited generator as compared to a self-excited generator

(a) is amenable to better voltage con-trol
(b) is more stable
(c) has exciting current independent of load current
(d) has all above features

Ans: d

19. In case of D.C. machines, mechanical losses are primary function of
(a) current  
(b) voltage
(c) speed
(d) none of above

Ans: c

20. Iron losses in a D.C. machine are independent of variations in
(a) speed
(b) load
(c) voltage
(d) speed and voltage

Ans: b

21. In D.C. generators, current to the external circuit from armature is given through
(a) commutator    
(b) solid connection
(c) slip rings
(d) none of above
Ans: a

23. Brushes of D.C. machines are made of
(a) carbon
(b) soft copper
(c) hard copper    
(d) all of above
Ans: a

24. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a)Blv
(b)Blv2
(c)Bl2v
(d)Bl2v2
Ans: a

25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
(a) 4
(b) 8
(c) 16
(d) 32
Ans: b

26. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: d

27. The insulating material used between the commutator segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating varnish
Ans: c

28. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a)     lie under south pole
(b)     lie under north pole
(c) lie under interpolar region
(d) are farthest from the poles
Ans: c

29. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
(a)     demagnetisation only
(b)     cross magnetisation as well as magnetisation
(c) crossmagnetisation as well as demagnetising
(d) cross magnetisation only
Ans: c

30. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising    
(d) none of above
Ans: a

31. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover
(b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
(d) all above
Ans: d

32. Eddy currents are induced in the pole shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and armature
(d) all above
Ans: c

33. In a D.C. machine, short-circuited field coil will result in
 (a)    odour of barning insulation
 (b)    unbalanced magnetic pull producing vibrations
 (c)  reduction of generated voltage for which excitation has to be increased to maintain the voltage
 (d)  all above
Ans:

34. Equilizer rings are required in case armature is
(a) wave wound    
(b) lap wound
(c) delta wound    
(d) duplex wound
Ans: b

35. Welding generator will have
(a) lap winding    
(b) wave winding
(c) delta winding
(d) duplex wave winding
Ans: a

36. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns
Ans: a

37. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a)     rotary converter
(b)     mercury are rectifier
(c) induction motor D.C. generator set
(d) synchronous motor D.C. generator set
Ans: c

38. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the magnetic path
(b) to spread out the flux to achieve uniform flux density
(c) to support the field coil
(d) to discharge all the above functions
Ans: d

39. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches
Ans: d

40. A D.C. welding generator has
(a) lap winding    
(b) wave moving
(c) duplex winding
(d) any of the above
Ans: a

41. Which of the following statement about D.C. generators is false ?
(a)     Compensating winding in a D.C. machine helps in commutation
(b)     In a D. C. generator interpoles winding is connected in series with the armature winding
(c)  Back pitch and front pitch are both odd and approximately equal to the pole pitch
(d)  Equilizing bus bars are used with parallel running of D.C. shunt generators
Ans: d

42. The demagnetising component of armature reaction in a D.C. generator
(a) reduces generator e.m.f.
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble
Ans: a

43. Magnetic field in a D.C. generator is produced by
(a) electromagnets
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above
Ans: a

44. The number of brushes in a commutator depends on
(a)     speed of armature
(b)     type of winding
(c)  voltage
(d)  amount of current to be collected
Ans: d

45. Compensating windings are used in D.C. generators
(a)     mainly to reduce the eddy currents by providing local short-circuits
(b)     to provide path for the circulation of cooling air
(c) to neutralise the cross-magnetising effect of the armature reaction
(d) none of the above
Ans: c

46. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?
(a) Dummy coils  
(b) Commutator
(c) Eye bolt
(d) Equilizer rings
Ans: b

47. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(a)     using conductor of annealed copper
(b)  using commutator with large number of segments
(c)  using carbon brushes of superior quality
(d)  using equiliser rings
Ans: c

48. In D.C. generators, lap winding is used for
(a) high voltage, high current
(b) low voltage, high current
(c) high voltage, low current
(d) low voltage, low current
Ans: b

49. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 2 : 3
(b) 3 : 1
(c) 3 : 2
(d) 1 : 3
Ans: b

50. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Graphite brushes
(b) Carbon brushes
(c) Metal graphite brushes
(d) None of the above
Ans: c

51. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be
(a) E/2
(b) 2E
(c) slightly less than E
(d) E
Ans: b

52. In a D.C. generator the actual flux distribution depends upon
(a) size of air gap
(b) shape of the pole shoe
(c) clearance between tips of the ad¬jacent pole shoes
(d) all of the above
Ans:

53. The armature core of a D.C. generator is usually made of
(a)     silicon steel    
(b)     copper
(c) non-ferrous material
(d) cast-iron
Ans: a

9.63. Satisfactory commutation of D.C. machines requires
(a) brushes should be of proper grade and size
(b) brushes should smoothly run in the holders
(c) smooth, concentric commutator properly undercut
(d) all of the above
Ans: d

54. Open circuited armature coil of a D.C. machine is
(a) identified by the scarring of the commutator segment to which open circuited coil is connected
(b) indicated by a spark completely around the commutator
(c) both (a) and (b)
(d) none of the above
Ans: c

55. In a D.C. machine, fractional pitch winding is used
(a)     to increase the generated voltage
(b)     to reduce sparking
(c)  to save the copper because of shorter end connections
(d)  due to (b) and (c) above
Ans:

56. For the parallel operation of two or more D.C. compound generators, we should ensure that
(a) voltage of the incoming generator should be same as that of bus bar
(b) polarity of incoming generator should be same as that of bus bar
(c) all the series fields should be run in parallel by means of equilizer connection
(d) series fields of all generators should be either on positive side or negative side of the armature
(e) all conditions mentioned above should be satisfied
Ans: d

57. D.C. series generator is used
(a)  to supply traction load
(b)  to supply industrial load at constant voltage
(c)     voltage at the toad end of the feeder
(d)     for none of the above purpose
Ans: c

58. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
(a)     series generator
(b)     shunt generator
(c)  compound generator
(d)  self-excited generator
Ans: d

59. Interpole flux should be sufficient to
(a) neutralise the commutating self induced e.m.f.
(b) neutralise the armature reaction flux
(c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
(d) perform none of the above functions
Ans: c

60. D.C. generator generally preferred for charging automobile batteries is
(a) series generator
(b) shunt generator
(c) long shunt compound generator
(d)    any of'the above
Ans: c

61. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
(a) r.p.m. is more than 300
(b) r.p.m. is less than 300
(c) number of poles is 4
(d) number of poles is 2
Ans: d

62. Permeance is the reciprocal of
(a) flux density    
(b) reluctance
(c) ampere-turns
(d) resistance
Ans: b

63. In D.C. generators the polarity of the interpoles
(a) is the same as that of the main pole ahead
(b) is the same as that of the immediately preceding pole
(c) is opposite to that of the main pole ahead
(d) is neutral as these poles do not play part in generating e.m.f.
Ans: a

64. The e.m.f. generated in a D.C. generator is directly proportional to
(a)     flux/pole
(b) speed of armature
(c) number of poles
(d) all of the above
Ans: b

65. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when
(a) there is no load on|he generator
(b) the generator runs on full load
(c) the generator runs on overload
(d) the generator runs on designed speed
Ans: a

66. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except
(a) interpoles
(b) dummy coils
(c) compensating winding
(d) shifting of axis of brushes
Ans: b

67. In D.C. generators on no-load, the air gap flux distribution in space is
(a) sinusoidal
(b) triangular
(c) pulsating
(d) flat topped
Ans: d

68. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly
(a) 150 V
(b) 175 V
(c) 240 V
(d) 290 V
Ans: c

69. The purpose of providing dummy coils in a generator is
(a) to reduce eddy current losses
(b) to enhance flux density
(c) to amplify voltage
(d) to provide mechanical balance for the rotor
Ans: d

70. In a shunt generator the voltage build up is generally restricted by
(a) speed limitation
(b) armature heating
(c) insulation restrictions
(d) saturation of iron
Ans:

71. If a D.C. generator fails to build up the probable cause could not be
(a) imperfect brush contact
(b) field resistance less than the critical resistance
(c) no residual magnetism in the generator
(d)   faulty shunt connections tending to reduce the residual magnetism
Ans: b

72. Flashing the field of D.C. generator means
(a) neutralising residual magnetism
(b) creating residual magnetism by a D.C. source
(c) making the magnetic losses of forces parallel
(d) increasing flux density by adding extra turns of windings on poles
Ans: b

73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
(a) 640 V
(b) 620 V
(c) 600 V
(d) 580 V
Ans: d

74. In a D.C. generator the critical resistance refers to the resistance of
(a) brushes
(b) field
(c) armature
(d) load
Ans: b

75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis
(b) in magnetic neutral axis
(c) just behind the magnetic neutral axis
Ans: a

76. Armature coil is short circuited by brushes when it lies
(a)     along neutral axis
(b)     along field axis
(c)   in any of the above positions
(d)     in none of the above positions
Ans: a

77. A cumulatively compounded long shunt generator when operating as a motor would be
(a) cumulatively compounded long shunt
(b) differentially compounded long shunt
(c) cumulatively compounded short shunt
(d) differentially  compounded  short shunt
Ans: b

78. To avoid formation of grooves in the commutator of a D.C. machine
(a) the brushes of opposite polarity should track each other
(b) the brushes of same polarity should track each other
(c) brush position has no effect on the commutator grooving
Ans: a

79. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two com-mutator bars
(6) Insulation failure between two turns of a coil
(c) Two of more turns of the same coil getting grounded
(d) All of the above
Ans: d

80. The rapid wear of brushes takes place due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) high mica insulation between com-mutation bars
(e) all of the above factors
Ans: e

81. Number of tappings for each equilizer ring is equal to
(a) number of pole pairs
(b) number of poles
(c) number of parallel paths
(d) number of commutator segments
Ans: a

82. A D.C. generator can be considered as
(a)     rectifier
(b)     primemover
(c) rotating amplifier
(d) power pump
Ans: c

83. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called
(a) rotor
(b) stator
(c) field
(d) armature
Ans: d

84. In a D.C. machine stray loss is the sum of
(a) total copper loss and mechanical loss
(b) armature copper loss and iron loss
(c) shunt field copper loss and mechanical loss
(d) iron loss and mechanical loss
Ans: d

85. Lap winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2
(d) that even number which is exact multiple of poles
Ans: a

86. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will
(a) increase
(b) decrease
(c) remain unaffected
(d) fluctuate heavily
Ans: b

87. An exciter for a turbo generator is a
(a) separately excited generator
(b) shunt generator
(c) series generator
(d) compound generator
Ans: b

88. In case of a flat compounded generator
(a) voltage generated is less than the rated voltage
(b) generated voltage is proportional to the load on the generator
(c) voltage remains constant irrespec¬tive of the load
(d) speed varies in proportion to the load on the generator
Ans: c

89. Which of the following generator will have negligible terminal voltage while running on no-load ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) Separately excited generator
Ans: a

90. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) None of the above
Ans: d

91. In over compounded generator, full load terminal voltage is
(a) almost zero
(b) less than noload terminal voltage
(c) more than noload terminal voltage
(d) equal to no-load terminal voltage
Ans: c

92. In a level compounded D.C. generator, full load terminal voltage is
(a)     negligibly low
(b) equal to no-load terminal voltage
(c) more than no-load terminal voltage
(d) less than no-load terminal voltage
Ans: b

93. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
(a) armature reaction
(b) armature resistance drop
(c) field weakening due to armature reaction and armature
(d) commutation
Ans: d

94. In a D.C. generator
(a) external resistance = internal char-acteristic - armature reaction
(b) internal characteristic = magnetisation characteristic - ohmic drop
(c) external characteristic = magnetisation characteristic - ohmic drop - armature reaction
(d) magnetisation characteristic = external characteristic
Ans: c

95. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave
(a) will be zero      
(b) will be of 5 Hz
(c) willbeof5xiVHz
(d) will be of v Hz 5
Ans: b

96. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
(a) zero
(b) about 2 V
(c) about 50 V
(d) 220 V
Ans: b

97. In a separately excited generator supplying rated load the armature reaction ,
(a) is always present
(b) is always absent
(c) may be sometimes present
(d) none of the above
Ans: a

98. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
(a) zero
(b) small
(c) the same as rated voltage
(d) high
Ans: a

99. Armature reaction in a generator results in
(a) demagnetisation of leading pole tip and magnetisation of trailing pole tip
(b) demagnetisation of trailing pole tip and magnetisation of leading pole tip
(c) damagnetising the centre of all poles
(d) magnetising the centre of all poles
Ans: a

100. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
(a) Series field
(b) Compensating field
(c) Inter pole field
(d) Shunt field
Ans: d

101. Wave winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2
(d) that even number which is exact multiple of poles
Ans: c

102. The critical resistance of the D.C. generator is the resistance of
(a) field
(b) brushes
(c) armature
(d) load
Ans: a

103. When two D.C. series generators are running in parallel, an equilizer bar is used
(a) to increase the speed and hence generated e.m.f.
(b) to increase the series flux
(c) so that two similar machines will pass approximately equal currents to the load
(d) to reduce the combined effect of ar-mature reaction of both machines
Ans: c

104. Which of the following generating machine will offer constant voltage on all loads ?
(a) Self-excited generator
(b) Separately excited generator
(c) Level compounded generator .
(d) All of the above
Ans: c

105. Which of the following generators will be preferred if they are required to be run in parallel ?
(a) Shunt generators
(b) Series generators
(c) Compound generators
(d) None of the above
Ans: a

106. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?
(a) The direction of that generator is reversed
(b) The speed of that generator is increased
(c) The field of that generator is weakened
(d) That generator takes large share of loads
Ans: d

107. A D.C. generator works on the principle of
(a)     Lenz's law
(b)     Ohm's law
(c)  Faraday's law of electromagnetic induction
(d)  none of the above
Ans: c

108. A series generator can self-excite
(a) only if the load current is zero
(b) only if the load current is not zero
(c) irrespective of the value of load current
(d) none of the above
Ans: b

109. A shunt generator can self-excite
(a) only if the resistance of the field circuit is less than critical value
(b) only if the resistance of the field circuit is greater than critical value
(c) irrespective of the value of the resis-tance in the field circuit
Ans: a

110. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
(a) 150 V
(b) less than 150 V
(c) greater than 150 V
(d) none of the above
Ans: c

111. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
(a) will be less than 250 V
(b) will always be 250 V
(c) may be greater or less than 250 V
(d) none of the above
Ans: c

112. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be
(a) 270 V
(b) 267.5 V
(c) 265 V
(d) 257.4 V
Ans: b

113. The  essential  condition for parallel operation of two D.C. generators is that they have '
(a)     same kW rating
(b)     the same operation r.p.m.
(c)  the same drooping voltage charac-teristics
(d)  same percentage regulation
Ans: c

114. When two D.C. generators are running in parallel an equilizer bar is used
(a) to increase the series flux
(b) to increase the generated e.m.f.
(c) to reduce the combined effect of ar-mature reaction of both the machines
(d) so that the two identical machines will pass approximately equal currents to the load
Ans: d

115. With a D.C. generator which of the following regulation is preferred ?
(a)     100% regulation
(b)     infinite regulation
(c) 50% regulation
(d) 1% regulation
Ans: d

116. Which generator would you prefer for feeding long D.C. transmission lines ?
(a) Series generator
(b) Shunt generator
(c) Over compound generator
(d) Flat compound generator
Ans: c

117. In a D.C. generator the critical resistance can be increased by
(a) increasing its field resistance
(b) decreasing its field resistance
(c) increasing its speed
(d) decreasing its speed
Ans: c

118. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is
(a) 2
(b) 4
(c) 6
(d) 8
Ans: b

119. For both lap and wave windings, there are as many commutator bars as the number of
(a) slots
(b) armature conductors
(c) winding elements
(d) poles
Ans: c

120. The series field of a short-shunt D.C. generator is excited by
(a) external current
(b) armature current
(c) shunt current
(d) load current
Ans: d

121. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately
(a) 40 percent
(b) 25 percent
(c) 10 percent
(d) 5 percent
Ans: d

122. Shunt generators are most suited for stable parallel operation because of their
(a)     rising voltage characteristics
(b)     identical voltage characteristics
(c) drooping voltage characteristics
(d) linear voltage characteristics
Ans: c

123. The main factor which leads to unstable parallel operation of flat and over compounded generators is
(a) their rising voltage characteristics
(b) unequal number of turns in their series field windings
(c) unequal speed regulation of their primemovers
(d) unequal series field resistances
Ans: a

124. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to
(a) reverse the field connections
(b) increase the field resistance
(c) increase the speed of primemover
(d) check armature insulation resis¬tance
Ans: a

EEE MCQ (Current Electricity)

Saturday, 6 October 2012

Current Electricity - electrical multiple choice questions and answers

1. The S.I. unit of power is
(a) henry
(b) coulomb
(c) watt
(d) watt-hour

Ans: c

2. Electric pressure is also called
(a) resistance
(b) power
(c) voltage
(d) energy

Ans: c

3. The substances whfch have a large number of free electrons and offer a low resistance are called
(a)     insulators
(b)     inductors
(c) semi-conductors
(d) conductors

Ans: d

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

Ans: b

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

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

7. Conductance is reciprocal of
(a) resistance
(b) inductance
(c) reluctance
(d) capacitance
Ans: a

8. The resistance of a conductor varies inversely as
(a) length
(6) area of cross-section
(c) temperature    
(d) resistivity
Ans: b

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

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

11. The resistance of a copper wire 200 m long is 21 Q. If its thickness (diameter) is 0.44 mm, its specific resistance is
around
(a) 1.2 x 10~8 Q-m
(b) 1.4 x 10~8 Q-m
(c) 1.6 x 10""8 Q-m
(d) 1.8 x 10"8 Q-m
Ans: 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
Ans:

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

14. In a circuit a 33 Q 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
Ans: 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 Q
(b) 600 Q
(c) 800 Q
(d) 1000 Q
Ans: 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 Q
(b) 36 Q
(c) 48 Q
(d) 64 Q
Ans: 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 Q. If the same four wires are connected is series the effective resistance will be
(a) 1 Q
(b) 2 Q
(c) 3 Q
(d) 4 Q
Ans: 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
Ans: 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 ^.s/m
(d) nearly 3 x 108 m/s
Ans: c

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

21. You have to replace 1500 Q resistor in radio. You have no 1500 Q resistor but have several 1000 Q 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
Ans: 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.
Ans: 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
Ans: d

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

26. Which is the best conductor of electricity ?
(a) Iron
(b) Silver
(c) Copper
(d) Carbon
Ans: b

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

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

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

31. Varistors are
(a)     insulators
(6)     non-linear resistors
(c) carbon resistors
(d) resistors with zero temperature coefficient
Ans: 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
Ans: b

33. The rating of a fuse wire is always expressed in
(a) ampere-hours
(b) ampere-volts
(c) kWh
(d) amperes
Ans: 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 (#) zero
Ans: 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
Ans: d

36. The filament of an electric bulb is made of
(a) carbon
(b) aluminium
(c) tungsten
(d) nickel
Ans: c

37. A 3 Q resistor having 2 A current will dissipate the power of
(a) 2 watts
(b) 4 watts
(c) 6 watts
(d) 8 watts
Ans: 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 resis¬tance in parallel is a voltmeter
(c) A galvanometer with low resistance in series is an ammeter
(d)     A galvanometer with high resis¬tance in series is an ammeter
Ans: 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
Ans: 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
Ans: 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
Ans: a

42. Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns open
(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
Ans: d

43. The four bulbs of 40 W each are connected in series wifti 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
Ans: a

44. Two resistances Rl and Ri are connected in series across the voltage source where R2>Ri. The largest drop
will be across
(a) R2
(b) Ri
(c) either Rl or Rz
(d) none of them
Ans: 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
Ans:

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

47. The hot resistance of the bulb's fila¬ment 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
Ans: c

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

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
Ans: c

50. The thickness of insulation provided on the conductor depends on
(a) the magnitude of voltage on the con-ductor
(b) the magnitude of current flowing through it
(c) both (a) and (b)
(d) none of the above
Ans: 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
Ans: 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
Ans: b

53. In an electric kettle water boils in 10m minutes. It is required to boil the boiler 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
Ans: 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
Ans: d

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

57. Resistance of a material always decreases if
(a)     temperature of material is decreased
(6)     temperature of material is increased
(c) number of free electrons available become more
(d) none of the above is correct
Ans: 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
Ans: 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
Ans: 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
Ans: 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
Ans: 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
Ans: d

63. It becomes more difficult to remove
(a) any electron from the orbit
(6) first electron from the orbit
(c) second electron from the orbit
(d) third electron from the orbit
Ans: d

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

67. Resistance of 220 V, 100 W lamp will be
(a) 4.84 Q
(b) 48.4 Q
(c) 484 ft
(d) 4840 Q
Ans: 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 con¬stant
Ans: 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
Ans: b

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

71. Bulbs in street lighting are all connected in
(a) parallel
(b) series
(c) series-parallel
(d) end-to-end
Ans: a

72. For testing appliances, the wattage of test lamp should be
(a) very low
(b) low
(c) high
(d) any value
Ans: 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 be¬tween contacts
(d) none of the above
Ans: a

74. Sparking occurs when a load is switched off because the circuit has high
(a) resistance
(b) inductance
(c) capacitance      
(d) impedance
Ans: 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
(e) 9 times
(d) unchanged
Ans: 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
Ans: b

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

78. A substance whose molecules consist of dissimilar atoms is called
(a) semi-conductor
(b) super-conducto
(c) compound
(d) insulator
Ans: 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
Ans: 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
Ans: b

91. Which method can be used for absolute measurement of resistances ?
(a) Lorentz method
(b) Releigh method
(c) Ohm's law method
(d) Wheatstone bridge method
Ans: d

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

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

95. A nichrome wire used as a heater coil has the resistance of 2 £2/m. 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
Ans: a

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

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

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 in¬sulation layer
(c) resistance of heater coil is more than the supply wires
(d) supply wires are made of superior material
Ans: 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
Ans: a

100. Which of the following statement is correct ?
(a) A semi-conductor is a material whose conductivity is same as be¬tween 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 con¬ducts only half of the applied voltage
(d)     A semi-conductor is a material made of alternate layers of conducting material and insulator
Ans: a

101. A rheostat differs from potentiometer in the respect that it
(a)     has lower wantage rating
(b)     has higher wattage rating
(c) has large number of turns
(d) offers large number of tappings
Ans: 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%
Ans: 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
Ans: 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) Semi-conductors
(d) Variable resistors
Ans: c

105. All good conductors have high
(a)     conductance    
(b)     resistance
(c) reluctance
(d) thermal conductivity
Ans: a

106. Voltage dependent resistors are usually made from
(a) charcoal
(b) silicon carbide
(c) nichrome
(d) graphite
Ans: c

107. Voltage dependent resistors are used
(a)     for inductive circuits
(6)     to supress surges
(c) as heating elements
(d) as current stabilizers
Ans: b

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

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

111. A thermistor has
(a) positive temperature coefficient
(b) negative temperature coefficient
(c) zero temperature coefficient
(d) variable temperature coefficient
Ans: c

112. If/, 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) I2R2t*
Ans: a

113. Nichrome wire is an alloy of
(a) lead and zinc
(b) chromium and vanadium
(c) nickel and chromium
(d) copper and silver
Ans: 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 n-mho
(b)     106 mho
(c)   1 milli-mho
(d)   none of the above
Ans: a

115. Which of the following can have negative temperature coefficient ?
(a) Compounds of silver
(6) Liquid metals
(c) Metallic alloys
(d) Electrolytes
Ans: d

116. Conductance : mho ::
(a)     resistance : ohm
(b)     capacitance : henry
(c) inductance : farad
(d) lumen : steradian
Ans: a

117. 1 angstrom is equal to
(a) 10-8 mm
(6) 10"6 cm
(c) 10"10 m
(d) 10~14 m
Ans: c

118. One newton metre is same as
(a) one watt
(b) one joule
(c) five joules
(d) one joule second
Ans: b