Mock test-4

Electrical Engineering (Code:8/10/17)

(Questions are based on SSC(JE), PSC(JE), BSNL(TTA), WBSEDCL, WBSETCL, WBPDCL, CIL State

and Central Service Examinations)

Note: Answer will be available after one week

Time Allowed: 1hours Maximum Marks: 100

1. An alternating current is given by i=10sin314t. the time taken by the current to reach a

value of 10A is

(a) 0.025sec

(b) 0.05sec

(c) 0.01sec

(d) 0.02sec

2. A wire is stretched to its double the length ,the new resistance will be

(a) 4 time the original resistance

(b) Double the original resistance

(c) Half the original resistance

(d) One-fourth the original resistance

3. When the frequency of supply voltage is increased the resistance of an inductor will

(a) Increase

(b) Decrease

(c) Remain same

(d) None

4. The ability of the material to set-up a magnetic field is called

(a) Permittivity

(b) Permeability

(c) Retentivity

(d) None

5. Capacity of battery is indicated by

(a) Ampere

(b) Volt-ampere

(c) Ampere-hour

(d) Watt

6. In a d.c. machine brushes are made of

(a) Carbon

(b) Graphite

(c) Copper

(d) None

7. If the field of a d.c. shunt motor running without load get opened then the motor will

(a) Stop

(b) Slow down

(c) Run normally

(d) Pick-up high speed

8. The specific gravity of the electrolyte of an lead acid battery gives an indication of

(a) The change of the battery

(b) The e.m.f. of the battery

(c) Level of electrolyte

(d) Damage caused to the plate

9. The material can be used for a permanent magnet is

(a) Alloy steel

(b) Soft iron

(c) Cast-iron

(d) Any of the above

10. D.C. series motor are best suited for electric traction as it

(a) Delivers High starting torque

(b) Runs at very high speed

(c) Cheaper in cost

(d) Consumes less power

11. The maximum value of sine wave current is 100 amps , the rms value of current is

(a) 7.07 amps

(b) 66.37 amps

(c) 70.72 amps

(d) 90 amps

12. The power factor of a circuit is 0.9 , the Q-factor will be

(a) 0.111

(b) 1

(c) 1.111

(d) None

13. The insulation resistance of a 240V wiring installation should not be less than

(a) 5MΩ

(b) 2MΩ

(c) 1MΩ

(d) 0.5MΩ

14. An ammeter can be used as voltmeter by using with it

(a) Shunt of high resistance

(b) Series of high resistance

(c) Shunt of low resistance

(d) Series of low resistance

15. In a circuit containing R,L and C, power loss takes place in

(a) L only

(b) C only

(c) R only

(d) All of above

16. Power factor of electric incandescent lamp is

(a) Lagging

(b) Unity

(c) Leading

(d) Zero

17. Full safety of an electrical installation is ensured when it is provided with

(a) Proper insulation

(b) Good earth

(c) Proper fuse in circuit

(d) All of above

18. To start a dc shunt motor below the rated speed, a resistance is inserted in series with

(a) Motor

(b) Armature

(c) Field winding

(d) Any of the above

19. For transmission over a long distance, high voltage is preferred because

(a) It requires conductor of less cross section area

(b) Copper loss is less

(c) Voltage regulation is better

(d) All of the above

20. Meter constant of an energy meter is expressed in the form of

(a) Number of revolutions/kW

(b) Number of revolutions/minute

(c) Number of revolutions/kWh

(d) kWh/revolution

21. The range of an ammeter can be increased by connecting with it

(a) A low resistance with series

(b) A high resistance with series

(c) A low resistance in parallel

(d) A high resistance in parallel

22. Which of the following is a nonlinear circuit parameter?

(a) Diode

(b) Capacitor

(c) Inductor

(d) Resistor

23. Which of the following elements is unilateral?

(a) Diode

(b) Capacitor

(c) Inductor

(d) Resistor

24. The current through the capacitor C across which a voltage is applied can be written as

(a) 1

𝑐

𝑑𝑣

𝑑𝑡

(b) 𝑐𝑑𝑣

𝑑𝑡

(c) 𝑐 ∫ 𝑣𝑑𝑡

(d) 1

𝑐∫𝑣𝑑𝑡

25. The energy stored in the magnetic field of an inductor L carrying a current i, is

(a) 1/2iL2

(b) 1/2Li2

(c) 1/2iL

(d) 1/2𝑖2

𝐿

26. A pure capacitance is connected across a voltage source. the current though it is out of

phase by

(a) 00

(b) 900

(c) 450

(d) 1800

27. A circuit component that opposes the instantaneous change in voltage is

(a) resistance

(b) capacitance

(c) inductance

(d) none

28. The form factor of sine wave is

(a) 1.0

(b) 1.1

(c) 1.21

(d) 1.5

29. Two sinusoidal current are given by i1= 10sin(ωt+ 𝜋

3) and i2=15sin(ωt-

𝜋

4). The phase

difference between them is

(a) 150

(b) 600

(c) 500

(d) 1050

30. Which of the following waves has unity form factor?

(a) Triangular wave

(b) Square wave

(c) Sine wave

(d) None

31. A resistance is connected across an ac voltage of 220V. the power dissipated will be

same if the resistor is connected across a dc voltage of

(a) 220V

(b) 110V

(c) 200V

(d) 50V

32. Dynamometer type instrument can be used for

a. AC work only

b. DC work only

c. Both ac and dc work

d. None of these

33. A Dynamometer type instrument is chiefly used as

a. DC ammeter

b. DC voltmeter

c. Watt meter

d. None of these

34. In a dynamometer type instrument, damping is provided by

a. Air friction

b. Eddy current

c. Fluid friction

d. None of these

35. Dynamometer type……………has uniform scale

a. Ammeter

b. Wattmeter

c. Voltmeter

d. None of these

36. If the current through operating coil of a moving iron instrument is doubled, the

operating force becomes

a. Two times

b. Four times

c. One-half time

d. Three times

37. For measuring high values of alternating current with a dynamometer, we use a

a. Shunt

b. Multiplier

c. Potential transformer

d. Current transformer

38. Hot-wire instrument have…………..scale

a. Uniform

b. Log

c. Squared

d. none of these

39. Moving iron instrument have…………….scale

a. Uniform

b. Log

c. Squared

d. none of these

40. The range of moving iron ammeter is extended by

a. Shunt

b. Multiplier

c. Changing number of turns of operating coil

d. None of these

41. To measure high frequency current we mostly use……………ammeter

a. Hot-wire

b. Dynamometer

c. Moving iron

d. Thermocouple

42. For measurement of high voltage DC we use…………….voltmeter

a. PMMC

b. Hot-wire

c. Electrostatic

d. Moving iron

43. In a dc machine number of commutator segments is equal to

a. Number of conductors

b. Twice the number of poles

c. Number of coils

d. None of these

44. High voltage dc machine use ……….. winding

a. Lap

b. Wave

c. Either lap or wave

d. None of these

45. In a lap winding the number of brushes required is equal to

a. Number of poles

b. Number of pairs of poles

c. Commutator pitch

d. None of these

46. An 8-pole, 250V, wave-wound generator has 400 conductors. If the generator is to be

lap-wound, the number of conductors required is

a. 800

b. 100

c. 3200

d. 1600

47. An 8-pole duplex lap winding will have………..parallel paths

a. 8

b. 4

c. 32

d. 16

48. A triplex wave winding will have………….parallel paths

a. 6

b. 2

c. 4

d. None of these

49. A 6-pole lap-wound generator has 300 conductors, the emf induced per conductor is 5V.

The induced emf if the generator is

a. 60V

b. 1500V

c. 360V

d. 250V

50. The armature conductors of a 6-pole, lap-wound dc generator are divided into

a. 2 parallel paths

b. 4 parallel paths

c. 3 parallel paths

d. 6 parallel paths

51. The efficiency of a dc machine is maximum when its variable loss is equal to

a. Constant loss

b. Half of constant loss

c. Double the constant loss

d. None of these

52. If the flux per pole of a dc generator is halved but its speed is doubled, its generated emf

will be

a. Halved

b. Remain the same

c. Doubled

d. None of these

53. A 30kW, 300V dc shunt generator has armature and filed resistance of 0.05Ω and 100Ω

respectively. What is the generated emf?

a. 295.25V

b. 311.25V

c. 305.15V

d. None of these

54. An external resistance is added in the series with the field of a dc shunt motor

a. To reduce the speed of the motor

b. To increase the speed of the motor

c. To reduce the armature current drawn by the motor

d. To reduce the losses

55. As the load is increased the speed of a dc shunt motor will

a. Remain constant

b. Increase proportionally

c. Increase slightly

d. Reduce slightly

56. If the current in the armature of a dc shunt motor is reduced to 5%, the torque of the

motor will be

a. 50% of the previous value

b. 25% of the previous value

c. 150% of the previous value

d. 125% of the previous value

57. In a dc shunt motor, if the terminal voltage is reduced to half and torque remains the

same, then

a. Speed will be half and armature current also will be half

b. Speed will be half but armature current remains the same

c. Speed will be half and armature current becomes double

d. Speed and armature current will remain the same

58. The direction of rotation of dc shunt motor is reversed by

a. Reversing armature connections

b. Interchanging the armature and filed connections

c. Reversing the supply

d. None of these

59. What happens if the field winding of a running shunt motor suddenly breaks open?

a. Its speed slow down

b. Its speed becomes dangerously high

c. It gives out sparks

d. It stops at once

60. If the back emf in a dc motor is absent, then

a. Motor will run at very high speed

b. Motor will run at very slow speed

c. Motor will not run at all

d. Motor will burn

61. The field flux of a dc motor can be controlled to achieve

a. The speed lower than the rated speed

b. The speed higher than the rated speed

c. The speed at rated speed

d. None of these

62. If the field of the dc shunt motor is opened

a. It will continue to run at rated speed

b. The of the motor will become very high

c. The motor will stop

d. None of these

63. Which of the following motors is used for rolling mills?

a. DC shunt motor

b. DC cummulative compound motor

c. DC series motor

d. DC differential compound motor

64. What will happen if the supply terminals of a dc shunt motor are interchanged?

a. Motor will stop

b. Motor will run at its normal speed in the same direction as it was running

c. The direction of rotation will reverse

d. None of these

65. Which of the following is a correct statement about eddy current

a. Eddy current improves the efficiency

b. Eddy currents are used for arc welding

c. Eddy currents heat up the metal parts

d. None of these

66. The steel for construction of transformer core is made to have

a. High permeability and low hysteresis

b. Low permeability and high hysteresis

c. Low permeability and low hysteresis

d. High permeability and high hysteresis

67. The no-load current of a transformer is terms of full load current is usually

a. 1 to 3%

b. 3 to 15%

c. 9 to 12%

d. 12 to 20%

68. The magnitude of mutual flux in a transformer is

a. Low at low load and high at high load

b. High at low load and low at high load

c. Same at all load

d. Varies at low load and constant at high load

69. If in a transformer the secondary turns are doubled and at the same time the primary

voltage is half, then the secondary voltage will be

a. Halved

b. Four times as high

c. Not change

d. Reduced to a quarter

70. What type of core is used in a high frequency transformer?

a. Open iron core

b. Air core

c. Closed iron core

d. None of these

71. The use of higher flux density in transformer design

a. Increase the weight per kVA

b. Decreases the weight per kVA

c. Increase the weight per kW

d. Decreases the weight per kW

72. The induced emf in the secondary of a transformer will depend on

a. Frequency of the supply only

b. Number turns in secondary only

c. Maximum flux in the core only

d. Frequency, flux and number of turns in the secondary

73. Two transformers are operating in parallel, they will share the load depending upon

their

a. Efficiency

b. Rating

c. Leakage reactance

d. Per-unit impedance

74. Why there is an enamel layer coated over the laminations of the transformer core

a. To decrease the hum

b. To attain adhesion between the laminations

c. To insulate the lamination against each other

d. To prevent the corrosion of the laminations

75. The full load copper loss and iron loss of a transformer are 6400watts and 5000watts

respectively. The copper loss and iron loss at half load will be

a. 3200watts and 2500watts

b. 3200watts and 5000watts

c. 1600watts and 1250watts

d. 1600watts and 5000watts

76. The N-type germanium semiconductor is obtained on doping intrinsic germanium by

a. Phosphorous

b. Boron

c. Aluminum

d. Gold

77. Recombination happens when

a. A valence electron jumps to conduction band from valence band

b. An electron falls into hole

c. A positive ion and negative ion bond together

d. All of these

78. The most commonly used semiconductor material is

a. Silicon

b. Boron

c. Germanium

d. Gallium arsenide

79. The process of adding impurity in an intrinsic semiconductor is known as

a. Doping

b. Diffusing

c. Mixing

d. All

80. The donor impurities

a. Generate electrons

b. Generate holes

c. Generate electrons and holes

d. None of these

81. The acceptor impurities

a. Generate electrons

b. Generate holes

c. Generate electrons and holes

d. None of these

82. When the pentavalent impurities just like phosphor are added to an intrinsic

semiconductor, it becomes

a. P-type semiconductor

b. N-type semiconductor

c. PN junction

d. All of these

83. When trivalent impurities just like boron, gallium or indium are added to intrinsic

semiconductor, it becomes

a. P-type semiconductor

b. N-type semiconductor

c. PN junction

d. All of these

84. A semiconductor is formed by

a. Covalent bond

b. Electrovalent bond

c. Co-ordinate bond

d. None of these

85. In a semiconductor, the energy gap between valence band and conduction band is

about

a. 5eV

b. 10eV

c. 15eV

d. 1eV

86. A semiconductor is generally has

a. 2 valence electrons

b. 4 valence electrons

c. 3 valence electrons

d. 6 valence electrons

87. When a pentavalent impurity is added to a pure semiconductor, it becomes

a. P-type semiconductor

b. N-type semiconductor

c. PN junction

d. Intrinsic

88. Addition of trivalent impurity to a pure semiconductor creates many

a. Free electrons

b. Valence electrons

c. Holes

d. All of these

89. A pentavalent impurity is called

a. Donor impurity

b. Acceptor impurity

c. Ionic impurity

d. None of these

90. PN junction acts as a

a. Unidirectional switch

b. Bi-directional switch

c. Controlled switch

d. None of these

91. The term bias means

a. Ratio of majority to minority carriers

b. Amount of current in PN junction

c. DC voltage applied to electronic device

d. None of these.

92. Electrostatic instruments are used as

a. Voltmeter only

b. Ammeters only

c. Both ammeters and voltmeters

d. Wattmeter only

93. An electric pyrometer is an instrument used to measure

a. Phase

b. Frequency

c. High temperature

d. None of these

94. The best type of meter movement is

a. Iron-vane

b. D’Arsonval

c. Dynamometer

d. None of these

95. Which instruments are most sensitive?

a. Moving iron

b. Hot-wire

c. Dynamometer

d. PMMC

96. In induction type ammeter………….damping is provided

a. Air friction

b. Eddy current

c. Fluid friction

d. None of these

97. The most commonly used induction type instrument is

a. Induction voltmeter

b. Induction wattmeter

c. Induction watt-hour meter

d. None of these

98. All voltmeter except ……….. voltmeters are operated by the passage of current

a. Moving-iron

b. Electrostatic

c. Dynamometer

d. PMMC

99. The watt-hour meter is ………………instrument

a. An integrating

b. An indicating

c. A recording

d. A transfer

100. For increasing the range of an ammeter, connect

a. A high value resistance in series with the ammeter coil

b. A high value resistance in parallel with the ammeter coil

c. A low value resistance in parallel with the ammeter coil

d. A low resistance in series with the ammeter coil

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