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

EEE MCQ (Cables)

Bottom of Form

Cables Multiple Choice Questions and Answers Preparation for Competition

1.    The insulating material for a cable should have
(a)    low cost   
(b)    high dielectric strength
(c)     high mechanical strength
(d)    all of the above
Ans: d

2.    Which of the following protects a cable against mechanical injury ?
(a)     Bedding   
(b)     Sheath
(c)     Armouring   
(d)     None of the above
Ans: c

3.    Which of the following insulation is used in cables ?
(a)    Varnished cambric   
(b)    Rubber   
(c)     Paper
(d)     Any of the above
Ans: d

4.    Empire tape is
(a)    varnished cambric
(b)    vulcanised rubber
(c)     impregnated paper
(d)     none of the above
Ans: a

5. The thickness of the layer of insulation on the conductor, in cables, depends upon
(a)     reactive power
(b)     power factor
(c)    voltage
(d)    current carrying capacity
Ans: c

6. The bedding on a cable consists of
(a)     hessian cloth    
(b)     jute
(c)    any of the above
(d)    none of the above
Ans: c

7. The insulating material for cables should
(a)     be acid proof
(b)     be non-inflammable
(c)    be non-hygroscopic
(d)    have all above properties
Ans: d

8.    In a cable immediately above metallic sheath _____ is provided.
(a)     earthing connection
(b)     bedding   
(c)     armouring
(d)     none of the above
Ans: b

9.    The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to
(a)     absence of harmonics
(b)     non-existence of any stability limit
(c)    smaller dielectric loss
(d)    absence of ripples
(e)    none of the above
Ans: c

10.   In case of three core flexible cable the colour of the neutral is
(a)     blue   
(b)     black
(c)    brown
(d)    none of the above
Ans: a

11    cables are used for 132 kV lines.
(a)     High tension   
(b)     Super tension
(c)    Extra high tension
(d)    Extra super voltage
Ans: d

12.    Conduit pipes are normally used to protect _____ cables.
(a)    unsheathed cables
(b)    armoured
(c)    PVC sheathed cables
(d)    all of the above
Ans: a

13.    The minimum dielectric stress in a cable is at
(a)     armour   
(b)     bedding
(c)    conductor surface
(d)    lead sheath
Ans: d

14.    In single core cables armouring is not done to
(a)     avoid excessive sheath losses
(b)     make it flexible
(c)    either of the above
(d)    none of the above
Ans: a

15.    Dielectric strength of rubber is around
(a)     5 kV/mm   
(b)     15 kV/mm
(c)     30 kV/mm   
(d)     200 kV/mm
Ans: c

16.    Low tension cables are generally used upto
(a)     200 V   
(b)     500 V
(c)     700 V   
(d)     1000 V
Ans: d

17.    In a cable, the maximum stress under operating conditions is at
(a)     insulation layer
(b)     sheath   
(c)     armour
(d)     conductor surface
Ans: d

18.    High tension cables are generally used upto
(a)     11kV   
(b)     33kV
(c)     66 kV   
(d)     132 kV
Ans: a

19.    The surge resistance of cable is
(a)     5 ohms   
(b)     20 ohms
(c)     50 ohms            
(d)     100 ohms
Ans: c

20.    PVC stands for
(a)     polyvinyl chloride
(b)     post varnish conductor
(c)    pressed and varnished cloth
(d)    positive voltage conductor
(e)    none of the above
Ans: a

    In the cables, the location of fault is usually found out by comparing
(a)    the resistance of the conductor
(b)    the inductance of conductors
(c)    the capacitances of insulated conductors
(d)    all above parameters
Ans: c

22.    In capacitance grading of cables we use a ______ dielectric.
(a)     composite   
(b)     porous
(c)     homogeneous    
(d)     hygroscopic
Ans: a

23.    Pressure cables are generally not used beyond
(a)     11 kV   
(b)     33 kV
(c)     66 kV   
(d)     132 kV
Ans: c

24.    The material for armouring on cable is usually
(a)     steel tape
(b)     galvanised steel wire
(c)    any of the above
(d)    none of the above
Ans: c

25.    Cables, generally used beyond 66 kV are
(a)     oil filled   
(b)     S.L. type
(c)     belted   
(d)     armoured
Ans: a

26.    The relative permittivity of rubber is
(a)    between 2 and 3
(b)    between 5 and 6
(c)    between 8 and 10
(d)    between 12 and 14
Ans: a

27.    Solid type cables are considered unreliable beyond 66 kV because
(a)     insulation may melt due to higher temperature
(b)     skin effect dominates on the conduc¬tor
(c)    of corona loss between conductor and sheath material
(d)    there is a danger of breakdown of insulation due to the presence of voids
Ans: d

28.    If the length of a cable is doubled, its capacitance
(a)    becomes one-fourth
(b)    becomes one-half
(c)    becomes double
(d)    remains unchanged
Ans: c

29.    In cables the charging current
(a)    lags the voltage by 90°
(b)    leads the voltage by 90°
(c)    lags the voltage by 180°
(d)     leads the voltage by 180°
Ans: b

30.    A certain cable has an insulation of relative permittivity 4. If the insulation is replaced by one of relative permittivity 2, the capacitance of the cable will become
(a)     one half   
(6)     double
(c)    four times   
(d)     none of the above
Ans: a

31.    If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be
(a)     5 kV/mm   
(b)     10 kV/mm
(a)     15 kV/mm   
(d)     30 kV/mm
Ans: b

32.    In the cables, sheaths are used to
(a)     prevent the moisture from entering the cable
(b)     provide enough strength
(e)    provide proper insulation
(d)    none of the above
Ans: a

33.    The intersheaths in the cables are used to
(a)     minimize the stress
(b)     avoid the requirement of good insulation
(c)    provide proper stress distribution
(d)    none of the above
Ans: c

34.    The electrostatic stress in underground cables is
(a)     same at the conductor and the sheath
(b)     minimum at the conductor and maximum at the sheath
(c)     maximum at the conductor and minimum at the sheath
(d)    zero at the conductor as well as on the sheath
(e)    none of the above
Ans: c

35.    The breakdown of insulation of the cable can be avoided economically by the use of
(a)    inter-sheaths
(b)    insulating materials with different dielectric constants
(c)    both (a) and (b)
(d)    none of the above
Ans: c

36.    The insulation of the cable decreases with
(a)    the increase in length of the insulation
(b)    the decrease in the length of the insulation
(c)    either (a) or (b)
(d)    none of the above
Ans: a

37.    A cable carrying alternating current has
(a)    hysteresis losses only
(b)    hysteresis and leakage losses only
(c)    hysteresis, leakage and copper losses only
(d)    hysteresis, leakage, copper and friction losses
Ans: b

38.    In a cable the voltage stress is maximum at
(a)     sheath   
(6)     insulator
(e)    surface of the conductor
(d)     core of the conductor
Ans: d

39.    Capacitance grading of cable implies
(a)    use of dielectrics of different permeabilities
(b)    grading according to capacitance of cables per km length
(c)    cables using single dielectric in different concentrations
(d)    capacitance required to be introduced at different lengths to counter the effect of inductance
(e)    none of the above
Ans: a

40.    Underground cables are laid at sufficient depth
(a)     to minimise temperature stresses
(b)     to avoid being unearthed easily due to removal of soil
(c)    to minimise the effect of shocks and vibrations due to gassing vehicles, etc.
(d)    for all of the above reasons
Ans: c

41.    The advantage of cables over overhead transmission lines is
(a)     easy maintenance
(b)     low cost
(c)    can be used in congested areas
(d)    can be used in high voltage circuits
Ans: c

42.    The thickness of metallic shielding on cables is usually
(a)     0.04 mm   
(b)     0.2 to 0.4 mm
(e)    3 to 5 mm   
(d)     40 to 60 mm
Ans: a

43.    Cables for 220 kV lines are invariably
(a)     mica insulated  
(b)     paper insulated
(c)    compressed oil or compressed gas insulated
(d)    rubber insulated
(e)    none of the above
Ans: c

44.    Is a cable is to be designed for use on 1000 kV, which insulation would you prefer ?
(a)     Polyvinyle chloride
(b)     Vulcanised rubber
(c)    Impregnated paper
(d)    Compressed SFe gas
(e)    none of the above
Ans: d

45.    If a power cable and a communication cable are to run parallel the minimum distance between the two, to avoid interference, should be
(a)     2 cm   
(b)     10 cm
(c)     50 cm   
(d)     400 cm
Ans: c

46.    Copper as conductor for cables is used as
(a)    annealed
(b)    hardened and tempered
(c)    hard drawn
(d)    alloy with chromium
Ans: a

47.    The insulating material should have
(a)    low permittivity
(b)    high resistivity
(c)    high dielectric strength
(d)    all of the above
Ans: d

48.    The advantage of oil filled cables is
(a)    more perfect impregnation
(b)    smaller overall size
(c)    no ionisation, oxidation and formation of voids
(d)    all of the above
Ans: d

49.    The disadvantage with paper as insulating material is
(a)     it is hygroscopic
(6)     it has high capacitance
(c)    it is an organic material
(d)    none of the above
Ans: a

50.    The breakdown voltage of a cable depends on
(a)     presence of moisture
(b)     working temperature
(c)    time of application of the voltage
(d)    all of the above
Ans: d

51.    It is difficult to maintain oil filled cables.
(a)   Yes
(b)   No
Ans: a

51.    In capacitance grading a homogeneous dielectric is used.   
(a)   Yes
(b)   No
Ans: b

52.    In congested areas where excavation is expensive and inconvenient 'draw in system' of laying of underground cables
is often adopted.
(a)   Yes
(b)   No
Ans: a

53.    Natural rubber is obtained from milky sap of tropical trees.
(a)   Yes
(b)   No
Ans: a

54.    Rubber is most commonly used insulation in cables.
(a)   Yes
(b)   No
Ans: a

55.    Polyethylene has very poor dielectric and ageing properties.   
(a)   Yes
(b)   No
Ans: b

56. The metallic sheath may be made of lead or lead alloy or of aluminium.
(a)   Yes
(b)   No
Ans: b

EEE MCQ (A.C. Fundamentals, Circuits and Circuit Theory)

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A.C. Fundamentals, Circuits and Circuit Theory - Electrical engineering multiple choice questions and answers for competitive exams

1. A sine wave has a frequency of 50 Hz. Its angular frequency is _______ radian/second.
(a) 100 n
(b) 50 jt
(c) 25 jt
(d) 5 n

Ans: a

2. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms.
(a) 2.5
(b) 5
(c) 10
(d) 15

Ans: c

3. The period of a wave is
(a)    the same as frequency
(6)    time required to complete one cycle
(c) expressed in amperes
(d) none of the above

Ans: b

4. The form factor is the ratio of
(a)    peak value to r.m.s. value
(6)    r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above

Ans: b

5. The period of a sine wave is _____ seconds.
Its frequency is
(a) 20 Hz
(b) 30 Hz
(c) 40 Hz
(d) 50 Hz

Ans: d

6. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to
(a)  average voltage
(b)  r.m.s. voltage  
(c)     peak voltage
(d)  none of the above
Ans: b

7. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is
(a) a sinusoid of the same frequency
(b) a sinusoid of half the original frequency
(c) a sinusoid of double the frequency
(d) not a sinusoid
Ans: a

8.   The peak value of a sine wave is 200 V. Its average value is
(a) 127.4 V
(b) 141.4 V
(c) 282.8 V
(d)200V
Ans: a

9. If two sine waves of the same frequency have a phase difference of JT radians, then
(a) both will reach their minimum values at the same instant
(b) both will reach their maximum values at the same instant
(c) when one wave reaches its maximum value, the other will reach its minimum value
(d) none of the above
Ans: c

10. The voltage of domestic supply is 220V. This figure represents
(a) mean value    
(b) r.m.s. value
(c) peak value
(d) average value
Ans: a

11. Two waves of the same frequency have opposite phase when the phase angle between them is
(a) 360°
(b) 180°
(c) 90°
(d) 0°
Ans: b

12. The power consumed in a circuit element will be least when the phase difference between the current and
voltage is
(a) 180"
(b) 90°
(c) 60°
(d) 0°
Ans: b

13. The r.m.s. value and mean value is the same in the case of
(a) triangular wave
(6) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c

14. For the same peak value which of the following wave will 'have the highest r.m.s. value ?
(a) square wave
(b) half wave rectified sine wave
(c) triangular wave
(d) sine wave
Ans: a

15. For the same peak value, which of the following wave has the least mean value ?
(a) half wave rectified sine wave
(b) triangular wave
(c) sine wave
(d) square wave
Ans: a

16. For a sine wave with peak value Imax the r.m.s. value is
(a) 0.5 Imax
(b) 0.707
(c) 0.9
(d) 1.414 Lmax
Ans: b

17. Form Factor is the ratio of
(a) average value/r.m.s. value
(b) average value/peak value
(e) r.m.s. value/average value
(d) r.m.s. value/peak value
Ans: c

18. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c

19. For a sine wave with peak value Emax______8.30. the average value is
(a) 0.636 Emax
(b) 0.707 Emax
(c) 0.434 EWc
(d) lAUEmax
Ans: a

20. For a frequency of 200 Hz, the time period will be
(a) 0.05 s
(b) 0.005 s
(c) 0.0005 s
(d) 0.5 s
Ans: b

21. The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that
(a) both waves must have same frequency
(b) both   waves  must  have identical peak values
(c) both waves must have zero value at the same time
(d) none of the above
Ans: a

22. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.
(a) 90
(b) 60
(c) 45
(d) 30
Ans: c

23. Capacitive reactance is more when
(a)     capacitance is less and frequency of supply is less
(b)     capacitance is less and frequency of supply is more
(c) capacitance is more and frequency of supply is less
(d) capacitance is more and frequency of supply is more
Ans: a

24. In a series resonant circuit, the impedance of the circuit is
(a) minimum
(b) maximum
(c) zero
(d) none of the above
Ans: a

25. Power factor of an electrical circuit is equal to
(a) R/Z
(b) cosine of phase angle difference between current and voltage
(c) kW/kVA
(d) ratio of useful current to total current Iw/I
(e) all above
Ans: e

26. The best place to install a capacitor is
(a) very near to inductive load
(b) across the terminals of the inductive load
(c) far away from the inductive load
(d) any where
Ans: b

27. Poor power factor
(a)     reduces load handling capability of electrical system
(b)     results in more power losses in the electrical system
(c)  overloads alternators, transformers and distribution lines
(d)  results in more voltage drop in the line
(e)  results in all above
Ans: e

28. Capacitors for power factor correction are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d

29. In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value
(a) will change the maximum value of current at resonance
(6) will change the resonance frequency
(c) will change the impedance at resonance frequency
(d) will increase the selectivity of the circuit
Ans: d

30. Pure inductive circuit
(a) consumes some power on average
(b) does not take power at all from a line
(c) takes power from the line during some part of the cycle and then returns back to it during other part of the cycle
(d) none of the above
Ans: c

31. Inductance affects the direct current flow
(a) only at the time of turning off
(b) only at the time of turning on
(c) at the time of turning on and off
(d) at all the time of operation
Ans: c

32. Inductance of a coil Varies
(a)     directly as the cross-sectional area of magnetic core
(b)     directly  as  square  of number of turns
(c) directly as the permeability of the core
(d) inversely as the length of the iron path
(e) as (a) to (d)
Ans: e

33. All the rules and laws of D.C. circuit also apply to A.C. circuit containing
(a) capacitance only
(b) inductance only
(c) resistance only
(d) all above
Ans: c

34. Time constant of an inductive circuit
(a) increases with increase of inductance and decrease of resistance
(b) increases with the increase of inductance and the increase of resistance
(c) increases with decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a

35. Power factor of an inductive circuit is usually improved by connecting capacitor to it in
(a) parallel
(b) series
(c) either (a) or (b)
(d) none of the above
Ans: a

36. In a highly capacitive circuit the
(a) apparent power is equal to the actual power
(b) reactive power is more than the apparent power
(c) reactive power is more than the actual powetf
(d) actual power is more than its reactive power
Ans: c

37. Power factor of the following circuit will be zero
(a) resistance
(b) inductance
(c) capacitance      
(d) both (b) and (c)
Ans: d

38. Power factor of the following circuit will be unity
(a) inductance
(b) capacitance
(c) resistance
(d) both (a) and (b)
Ans: c

39. Power factor of the system is kept high
(a) to reduce line losses
(b) to maximise the utilization of the capacities of generators, lines and transformers
(c) to reduce voltage regulation of the line
(d) due to all above reasons
Ans: d

40. The time constant of the capacitance circuit is defined as the time during which voltage
(a) falls to  36.8% of its final steady value
(b) rises to 38.6% of its final steady value
(c) rises to 63.2% of its final steady value
(d) none of the above
Ans: c

41. In a loss-free R-L-C circuit the transient current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c

42. The r.m.s. value of alternating current is given by steady (D.C.) current which when flowing through a given circuit for a given time produces
(a) the more heat than produced by A.C. when flowing through the same circuit
(b) the same heat as produced by A.C. when flowing through the same circuit
(c) the less heat than produced by A.C. flowing through the same circuit
(d) none of the above
Ans: b

43. The square waveform of current has following relation between r.m.s. value and average value.
(a) r.m.s. value is equal to average value
(b) r.m.s. value of current is greater than average value
(c) r.m.s. value of current is less than average value
(d) none of the above
Ans: a

44. The double energy transient occur in the
(a) purely inductive circuit
(b) R-L circuit
(c) R-C circuit
(d)     R-L-C circuit
Ans: d

45. The transient currents are associated with the
(a) changes in the stored energy in the inductors and capacitors
(b) impedance of the circuit
(c) applied voltage to the circuit
(d) resistance of the circuit
Ans: a

46. The power factor at resonance in R-L- C parallel circuit is
(a) zero
(b) 0.08 lagging
(c) 0.8 leading
(d) unity
Ans: d

47. In the case of an unsymmetrical alternating current the average value must always be taken over
(a) unsymmetrical part of the wave form
(b) the quarter cycle
(c) the half cycle
(d) the whole cycle
Ans: d

48. In a pure resistive circuit
(a) current lags behind the voltage by 90°
(b) current leads the voltage by 90°
(c) current can lead or lag the voltage by 90°
(d)     current is in phase with the voltage
Ans: d

49. In a pure inductive circuit
(a) the current is in phase with the voltage
(b) the current lags behind the voltage by 90°
(c) the current leads the voltage by 90°
(d) the current can lead or lag by 90°
Ans: b

50. In a circuit containing R, L and C, power loss can take place in
(a) C only
(b) L only
(c) R only
(d) all above
Ans: c

51. Inductance of coil
(a) is unaffected by the supply frequency
(b) decreases with the increase in supply frequency
(c) increases with the increase in supply frequency
(d) becomes zero with the increase in supply frequency
Ans: c

52. In any A.C. circuit always
(a) apparent power is more than actual power
(b) reactive power is more than apparent power
(c) actual power is more than reactive power
(d) reactive power is more than actual power
Ans: a

53. Which of the following circuit component opposes the change in the circuit voltage ?
(a) Inductance      
(b) Capacitance
(c) Conductance    
(d) Resistance
Ans:

54. In a purely inductive circuit
(a) actual power is zero
(b) reactive power is zero
(c) apparent power is zero
(d) none of above is zero
Ans: a

55. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d

56. Pure inductive circuit takes power from the A.C. line when
(a) applied voltage decreases but cur¬rent increases
(b) applied voltage increases but cur¬rent decreases
(c) both applied voltage and current increase
(d) both applied voltage and current decrease
Ans: a

57. Time constant of a circuit is the time in seconds taken after the application of voltage to each
(a) 25% of maximum value
(b) 50% of maximum value
(c)     63% of maximum value
(d)     90% of the maximum value
Ans: c

58. Time constant of an inductive circuit
(a)     increases with increase of inductance and decrease of resistance
(b)     increases with the increase of inductance and the increase of resistance
(c) increases with the decrease of inductance and decrease of resistance
(d) increases with decrease of inductance and increase of resistance
Ans: a

59. Time constant of a capacitive circuit
(a)     increases with the decrease of capacitance and decrease of resistance
(b)     increases with the decrease of capacitance and increase of resis¬tance
(c) increases with the increase of capacitance and decrease of resis¬tance
(d) increase with increase of capacitance and increase of resis¬tance
Ans: d

60. Magnitude of current at resonance in R-L-C circuit
(a) depends upon the magnitude of R
(b) depends upon the magnitude of L
(c) depends upon the magnitude of C
(d) depends upon the magnitude of R, LandC
Ans: a

61. In a R-L-C circuit
(a) power is consumed in resistance and is equal to I R
(b) exchange of power takes place between inductor and supply line
(c) exchange of power takes place between capacitor and supply line
(d) exchange of power does not take place between resistance and the supply line
(e)     all above are correct
Ans: e

62. In R-L-C series resonant circuit magnitude of resonance frequency can be changed by changing the value of
(a) R only
(b) L only
(c) C only
(d) L or C
(e) R,L or C
Ans: d

63. In a series L-C circuit at the resonant frequency the
(a)    current is maximum
(b)    current is minimum
(c)  impedance is maximum
(d)  voltage across C is minimum
Ans: a

64. The time constant of a series R-C circuit is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c

65. If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be
(a) 0.001 s
(b) 0.1 s
(c) 10 s
(d) 100 s
Ans: b

66. Which of the following coil will have large resonant frequency ?
(a) A coil with large resistance
(b) A coil with low resistance
(c) A coil with large distributed capacitance
(d) A coil with low distributed capacitance
Ans: c

67. If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave ?
(a) 42.42 sin 3141
(b) 60 sin 25 t
(c) 30 sin 50 t
(d) 84.84 sin 25 t
Ans: a

68. The safest value of current the human body can carry for more than 3 second is
(a) 4 mA
(b) 9 mA
(c) 15 mA
(d) 25 mA
Ans: b

69. A pure inductance connected across 250 V, 50 Hz supply consumes 100 W.
This consumption can be attributed to
(a) the big size of the inductor
(b) the reactance of the inductor
(c) the current flowing in the inductor
(d) the statement given is false
Ans: d

70. The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA
The power drawn by the circuit is
(a) 12 kW
(b) 22 kW
(c) 32 kW
(d) 64 kW
Ans: c

71. The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of
(a)     iron loss in core
(b)     skin effect
(c) increase in temperature
(d) capacitive effect between adjacent coil turns
Ans: a

72. In an AC. circuit, a low value of kVAR compared with kW indicates
(a) low efficiency
(b) high power factor
(c) unity power factor
(d) maximum load current
Ans: b

73. In AC. circuits, laminated iron is invariably used in order to
(a) reduce eddy current loss
(b) increase heat radiation
(c) make assembly cheap and easier
(d) reduce circuit permeability
Ans: a

74. The ratio of active power to apparent power is known as factor.
(a) demand
(b) load
(c) power
(d) form
Ans: c

75. All definitions of power factor of a series R-L-C circuit are correct except
(a)     ratio of net reactance and impedance
(b)     ratio of kW and kVA
(c) ratio of J and Z
(d) ratio of W and VA
Ans: a

76. The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is
(a) 4 kVAR
(b) 6 kVAR
(c) 8 kVAR
(d) 16 kVAR
Ans: b

77. What will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value ?
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Ans: c

78. The purpose of a parallel circuit resonance is to magnify
(a) current
(b) voltage
(c) power
(d) frequency
Ans: b

79. In an A.C. circuit power is dissipated in
(a)     resistance only
(b)     inductance only
(c) capacitance only
(d) none of the above
Ans: a

80. In a parallel R-C circuit, the current always______the applied voltage
(a)     lags
(b)     leads
(c) remains in phase with
(d) none of the above
Ans: b

81. At very low frequencies a series R-C circuit behaves as almost purely
(a)     resistive
(b)     inductive
(c) capacitive
(d) none of the above
Ans: c

82. Skin effect occurs when a conductor carries current at _____ frequencies.
(a) very low
(b) low
(c) medium
(d) high
Ans: d

83. At ______ frequencies the parallel R-L circuit behaves as purely resistive.
(a) low
(b) very low
(c) high
(d) very high
Ans: d

84. In a sine wave the slope is constant
(a)     between 0° and 90°
(b)     between 90° and 180°
(c)  between 180° and 270°
(d)  no where
Ans: d

85. The  power is measured in terms of decibles in case of
(a)     electronic equipment
(b)     transformers
(c) current transformers
(d) auto transformers
Ans: a

86. Capacitive susceptance is a measure of
(a)     reactive power in a circuit
(b)     the extent of neutralisation of reactive power in a circuit
(c) a purely capacitive circuit's ability to pass current
(d) a purely capacitive circuit's ability to resist the flow of current
Ans: c

87. Which of the following statements pertains to resistors only ?
(a)     can dissipate considerable amount of power
(6)     can act as energy storage devices
(c) connecting them in parallel in¬creases the total value
(d) oppose sudden changes in voltage
Ans: a

88. Which of the following refers to a parallel circuit ?
(a)     The current through each element is same
(b)     The voltage across element is in proportion to it's resistance value
(c) The equivalent resistance is greater than any one of the resistors
(d) The current through any one element is less than the source current
Ans: d

89. Aphasoris
(a) a line which represents the mag¬nitude and phase of an alternating quantity
(b) a line representing the magnitude and direction of an alternating quantity
(c)     a coloured tag or band for distinction between different phases of a 3-phase supply
(d)     an instrument used for measuring phases of an unbalanced 3-phase load
Ans: a

89. A parallel AC. circuit in resonance will
(a) have a high voltage developed across each inductive and capacitive section
(b) have a high impedance
(c) act like a resistor of low value
(d) have current in each section equal to the line current
Ans: b

90. Wire-wound resistors are unsuitable for use at high frequencies because they
(a) create more electrical noise
(b) are likely to melt under excessive eddy current heat
(c) consume more power
(d) exhibit unwanted inductive and capacitive effects
Ans: d

91. The inductance of a coil can be increased by
(a)     increasing core length
(b)     decreasing the number of turns
(c) decreasing the diameter of the former
(d) choosing core material having high relative permeability
Ans: d

92. In a three-phase supply floating neutral is undesirable because it way give rise to
(a) high voltage across the load
(b) low voltage across the load
(c) unequal line voltages across the load
Ans: c

93. Which of the following waves has the highest value of peak factor ?
(a) Square wave  
(b) Sine wave
(c) Half wave rectified sine wave
(d) Triangular wave
Ans: c

94. The frequency of domestic power supply in India is
(a) 200 Hz
(b) 100 Hz
(c) 60 Hz
(d) 50 Hz
Ans: d

95. The r.m.s. value of half wave rectified sine wave is 200 V. The r.m.s. value of full wave rectified AC. will be
(a) 282.8 V
(b) 141.4 V
(c) 111 V
(d) 100 V
Ans: a

96. The r.m.s. value of pure cosine function is
(a) 0.5 of peak value
(b) 0.707 of peak value
(c) same as peak value
(d) zero
Ans: b

97. Ohm is unit of all of the following except
(a) inductive reactance
(b) capacitive reactance
(c) resistance
(d)     capacitance
Ans: d

98. The series ;nd parallel resonance on L-C circui' differs in that
(a) series resistance needs a low-resistance ource for sharp rise in current
(b) series resonance needs a high-resistance source for sharp increase in current
(c) parallel resonance needs a low-resistance source for a sharp in¬crease in impedance
(d) parallel resonance needs a low-resistance source for a sharp rise in line current
Ans: a

99. The phasors for which of the following pair are 180° out of phase for VL, VC and VR?
(a) Vc and VR
(b) VL and VR
(c) Vc and VL
(d) none of the above
Ans: c

100.   The frequency of an alternating current is
(a) the speed with which the alternator runs
(b) the number of cycles generated in one minute
(c) the number of waves passing through a point in one second
(d) the number of electrons passing through a point in one second
Ans: c

101. A pure capacitor connected across an A.C. voltage consumed 50 W. This is due to
(a) the capacitive reactance in ohms
(b) the current flowing in capacitor
(c) the size of the capacitor being quite big
(d) the statement is incorrect
Ans: d

102. The power factor of a D.C. circuit is always
(a) less than unity
(b) unity
(c) greater than unity
(d) zero
Ans: b

103. The product of apparent power and cosine of the phase angle between circuit voltage and current is
(a) true power
(b) reactive power
(c) volt-amperes
(d) instantaneous power
Ans: a

104. The equation of 50 Hz current sine wave having r.m.s. value of 60 A is
(a) 60 sin 25 t
(b) 60 sin 50 t
(c) 84.84 sin 3141
(d) 42.42 sin 314 t
Ans: c

105. An A.C. voltage is impressed across a pure resistance of 3.5 ohms in parallel with a pure inductance of impedance of 3.5 ohms,
(a) the current through the resistance is more
(b) the current through the resistance is less
(c) both resistance and inductance carry equal currents
(d) none of the above
Ans: c

106. In a pure inductive circuit if the supply frequency is reduced to 1/2, the current will
(a)     be reduced by half
(b)     be doubled
(c) be four times as high
(d) be reduced to one fourth
Ans: b

107. In a pure capacitive circuit if the supply frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times at high
(d) be reduced to one fourth
Ans: a

108. When an alternating current passes through an ohmic resistance the electrical power converted into heat is
(a) apparent power
(b) true power
(c) reactive power
(d) none of the above
Ans: b

109. In each of the three coils of a three phase generator, an alternating voltage having an r.m.s. value of 220 V is induced. Which of the following values is indicated by the voltmeters ?
(a)     220 V
(b)     220V3V
(c) 220/V3 V
(d) none of the above
Ans: a