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Top 100 MCQ Measuring Instrument
Top 100 MCQ
For all competitive exam.
1. Which of the following properties a damping oil must possess ?
(a) Must be a good insulator
(b) Should be non-evaporating
(c) Should not have corrosive action upon the metal of the vane
(d) The viscosity of the oil should not change with the
temperature
(e) All of the above
Ans: e
2. A moving-coil permanent-magnet instrument can be used as _____ by using a low resistance shunt.
(a) ammeter
(b) voltmeter
(c) flux-meter
(d) ballistic galvanometer
Ans: a
3. A moving-coil permanent-magnet instrument can be used as flux-meter……
(a) by using a low resistance shunt
(b) by using a high series resistance
(c) by eliminating the control springs
(d) by making control springs of large moment of inertia
Ans: c
4. Which of the following devices may be used for extending the range of instruments?
(a) Shunts
(b) Multipliers
(c) Current transformers
(d) Potential transformers
(e) All of the above
Ans: e
5. An induction meter can handle current up to……
(a) 10 A
(b) 30 A
(c) 60 A
(d) 100 A
Ans: d
6. For handling greater currents induction wattmeters are used in conjunction with……
(a) potential transformers
(b) current transformers
(c) power transformers
(d) either of the above
(e) none of the above
Ans: b
7. Induction type single phase energy meters measure electric energy in……
(a) kW
(b) Wh
(c) kWh
(d) VAR
(e) None of the above
Ans: c
8. Most common form of A.C. meters met with in every day domestic and industrial installations are……
(a) mercury motor meters
(b) commutator motor meters
(c) induction type single phase energy meters
(d) all of the above
Ans: c
9. Which of the following meters are not used on D.C. circuits……
(a) Mercury motor meters
(b) Commutator motor meters
(c) Induction meters
(d) None of the above
Ans: c
10. Which of the following is an essential part of a motor meter ?
(a) An operating torque system
(b) A braking device (c) Revolution registering device
(d) All of the above
Ans: d
11. A potentiometer may be used for……
(a) measurement of resistance
(b) measurement of current
(c) calibration of ammeter
(d) calibration of voltmeter
(e) all of the above
Ans: e
12. Resistances can be measured with the help of……
(a) wattmeter
(b) voltmeters
(c) ammeters
(d) ohmmeters and resistance bridges
(e) all of the above
Ans: d
13 According to application, instruments are classified
as……
(a) switch board
(b) portable
(c) both (a) and (b)
(d) moving coil
(e) moving iron
(f) both (d) and (e)
Ans: c
14. Which of the following essential features is possessed by an indicating instrument?
(a) Deflecting device
(b) Controlling device
(c) Damping device
(d) All of the above Ans: d
15. A _____ device prevents the oscillation of the moving system and enables the latter to reach its final position quickly
(a) deflecting
(b) controlling
(c) damping
(d) any of the above
Ans: c
16. The spring material used in a spring control device should have the following property. ……
(a) Should be non-magnetic
(b) Most be of low temperature co-efficient
(c) Should have low specific resistance
(d) All of the above
Ans:d
17. The use of _____ instruments is merely confined within laboratories as standardizing instruments.
(a) absolute
(b) indicating
(c) recording
(d) integrating
(e) none of the above
Ans: a
18. Which of the following instruments indicate the instantaneous value of the electrical quantity being measured at the time at which it is being measured?
(a) Absolute instruments
(b) Indicating instruments
(c) Recording instruments
(d) Integrating instruments
Ans: b
19. _____ instruments are those which measure the total quantity of electricity delivered in a particular time.
(a) Absolute
(b) Indicating
(c) Recording
(d) Integrating
Ans: d
20. Which of the following are integrating instruments?
(a) Ammeters
(b) Voltmeters
(c) Wattmeter
(d) Ampere-hour and watt-hour meters
Ans: d
21. In a Weston synchronoscope, the fixed coils are connected across……
(a) bus-bars
(b) incoming alternator
(c) a lamp
(d) none of the above
Ans: b
22. In Weston synchronoscope the moving coil is connected across……
(a) bus-bars
(b) incoming alternator
(c) fixed coils
(d) any of the above
Ans: a
23. The power factor of a single phase load can be calculated if the instruments available are……
(a) one voltmeter and one ammeter
(b) one voltmeter, one ammeter and one wattmeter
(c) one voltmeter, one ammeter and one energy meter
(d) any of the above
Ans: b
24. The desirable static characteristics of a measuring system are……
(a) accuracy and reproducibility
(b) accuracy, sensitivity and reproducibility
(c) drift and dead zone
(d) static error
Ans: b
25. Damping of the Ballistic galvanometer is made small to……
(a) get first deflection large
(b) make the system oscillatory
(c) make the system critically damped
(d) get minimum overshoot
Ans: a
26. If an instrument has cramped scale for larger values, then it follows……
(a) square law
(b) logarithmic law
(c) uniform law
(d) none of the above
Ans: b
27. Volt box is a component to……
(a) extend voltage range
(6) measure voltage
(c) compare voltage in a box
(d) none of the above
Ans: a
28. E.m.f. of a Weston cell is accurately measured by……
(a) electrostatic voltmeter
(b) hot wire voltmeter
(c) isothermal voltmeter
(d) electrodynamic voltmeter
Ans: a
29. The gravity-controlled instrument has crowded scale because current is proportional to……
(a) balancing weight
(b) deflection angle
(c) sine of deflection angle
Ans: c
30. A sensitive galvanometer produces large deflection for a……
(a) small value of current
(b) large value of current
(c) large value of power
(d) large value of voltage
(e) none of the above
Ans: a
31. A multirange instrument has……
(a) multiple shunt or series resistances inside the meter
(b) multicoil arrangement
(c) variable turns of coil
(d) multi range meters inside the measurement system
(e) any of the above
Ans: a
32. The rectifier instrument is not free from……
(a) temperature error
(b) wave shape error
(c) frequency error
(d) all of the above
Ans: c
33. Alternating current is measured by……
(a) induction ammeter
(b) permanent magnet type ammeter
(c) electrostatic ammeter
(d) moving iron repulsion type voltmeter
Ans: a
34. Most sensitive galvanometer is……
(a) elastic galvanometer
(b) vibration galvanometer
(c) Duddlb galvanometer
(d) spot ballistic galvanometer
Ans: d
35. Instrument transformers are……
(a) potential transformers
(b) current transformers
(c) both (a) and (b)
(d) power transformers
Ans: c
36. The ratio of maximum displacement deviation to full scale deviation of the instrument is called……
(a) static sensitivity
(b) dynamic deviation
(c) linearity
(d) precision or accuracy
Ans: c
37. Systematic errors are……
(a) instrumental errors
(b) environmental errors
(c) observational errors
(d) all of the above
Ans: d
38. Standard resistor is made from……
(a) platinum
(b) maganin
(c) silver
(d) nichrome
Ans: b
39. Commonly used standard capacitor is……
(a) spherical type
(b) concentric cylindrical type
(c) electrostatic type
(d) multilayer parallel plate type
Ans: b
40. Operating torques in analogue instruments are……
(a) deflecting and control
(b) deflecting and damping
(c) deflecting, control and damping
(d) vibration and balancing
Ans: c
41. Commonly used instruments in power system measurement are……
(a) induction
(b) moving coil or iron
(c) rectifier
(d) electrostatic
Ans: a
42. For measurements on high voltage capacitors, the suitable bridge is……
(a) Wein bridge
(b) Modified De Santy’s bridge
(c) Schering bridge
(d) Any of the above
(e) None of the above
Ans: c
43. In an Anderson bridge, the unknown inductance is measured in terms of……
(a) known inductance and resistance
(b) known capacitance and resistance
(c) known resistance
(d) known inductance
Ans: b
44. Murray loop test can be used for location of……
(a) ground fault on a cable
(b) short circuit fault on a cable
(c) both the ground fault and the short-circuit fault
(d) none of the above
Ans: c
45. Which of the following devices should be used for accurate measurement of low D.C. voltage ?
(a) Small range moving coil voltmeter
(b) D.C. potentiometer
(c) Small range thermocouple voltmeter
(d) None of the above
Ans: b
46. It is required to measure the true open circuit e.m.f. of a battery. The best device is……
(a) D.C. voltmeter
(b) Ammeter and a known resistance
(c) D.C. potentiometer
(d) None of the above
Ans: c
47. A voltage of about 200 V can be measured……
(a) directly by a D.C. potentiometer
(b) a D.C. potentiometer in conjunction with a volt ratio box
(c) a D.C. potentiometer in conjunction with a known resistance
(d) none of the above
Ans: b
48. A direct current can be measured by……
(a) a D.C. potentiometer directly
(b) a D.C. potentiometer in conjunction with a standard
resistance
(c) a D.C. potentiometer in conjunction with a volt ratio box
(d) none of the above
Ans: b
49. To measure a resistance with the help of a potentiometer it is……
(a) necessary to standardise the potentiometer
(b) not necessary to standardise the potentiometer
(c) necessary to use a volt ratio box in conjunction with the
potentiometer
(d) none of the above
Ans: b
50. A phase shifting transformer is used in conjunction with……
(a) D.C. potentiometer
(b) Drysdale potentiometer (c) A.C. co-ordinate potentiometer
(d) Crompton potentiometer
Ans: b
51. Basically a potentiometer is a device for……
(a) comparing two voltages
(b) measuring a current
(c) comparing two currents
(d) measuring a voltage
(e) none of the above
Ans: a
52. In order to achieve high accuracy, the slide wire of a potentiometer should be……
(a) as long as possible
(b) as short as possible
(c) neither too small not too large
(d) very thick
Ans: a
53. To measure an A. C. voltage by using an A.C. potentiometer, it is desirable that the supply for the potentiometer in taken……
(a) from a source which is not the same as the unknown voltage
(b) from a battery
(c) from the same source as the unknown voltage
(d) any of the above
Ans: c
54. For measurements on high voltage capacitors, the suitable bridge is……
(a) Wein bridge
(b) Modified De Santy’s bridge
(c) Schering bridge
(d) Any of the above
(e) None of the above
Ans: c
55. In an Anderson bridge, the unknown inductance is measured in terms of……
(a) known inductance and resistance
(b) known capacitance and resistance
(c) known resistance
(d) known inductance
Ans: b
56. Wagner earthing device is used to eliminate errors due to……
(a) electrostatic coupling
(b) electromagnetic coupling
(c) both (a) and (b)
(d) none of the above
Ans: a
57. For measurement of mutual inductance we can use……
(a) Anderson bridge
(b) Maxwell’s bridge
(c) Heaviside bridge
(d) Any of the above
Ans: c
58. For measurement of inductance having high value, we should use……
(a) Maxwell’s bridge
(b) Maxwell Wein bridge
(c) Hay’s bridge
(d) Any of the above
Ans: c
59. If the current in a capacitor leads the voltage by 80°, the loss angle of the capacitor is……
(a) 10°
(b) 80°
(c) 120°
(d) 170°
Ans: a
60. In a Schering bridge the potential of the detector above earth potential is……
(a) a few volts only
(6) 1 kV
(c) 5 kV
(d) 10 kV
Ans: a
61. To avoid the effect of stray magnetic field in A.C. bridges we can use……
(a) magnetic screening
(b) Wagner earthing device
(c) wave filters
(d) any of the above
Ans: a
62. If an inductance is connected in one arm of bridge and resistances in the remaining three arms……
(a) the bridge can always be balanced
(b) the bridge cannot be balanced
(c) the bridge can be balanced if the resistances have some
specific values
Ans: b
63. A power factor meter has……
(a) one current circuit and two pressure circuits
(b) one current circuit and one pressure circuit
(c) two current circuits and one pressure circuit
(d) none of the above
Ans: a
64. The two pressure coils of a single phase power factor meter have……
(a) the same dimensions and the same number of turns
(b) the same dimension but different number of turns
(c) the same number of turns but different dimensions
(d) none of the above
Ans: a
65. In a single phase power factor meter the phase
difference between the currents in the two pressure coils is……
(a) exactly 0°
(b) approximately 0°
(c) exactly 90°
(d) approximately 90°
Ans: c
66. In a dynamometer 3-phase power factor meter, the
planes of the two moving coils are at……
(a) 0°
(b) 60°
(c) 90°
(d) 120°
Ans: d
67. In a vibrating reed frequency meter the natural frequencies of two adjacent reeds have a difference of……
(a) 0.1 Hz
(b) 0.25 Hz
(c) 0.5 Hz
(d) 1.5 Hz
Ans: c
68. In a Weston frequency meter, the magnetic axes of the two fixed coils are……
(a) parallel
(b) perpendicular
(c) inclined at 60°
(d) inclined at 120°
Ans: b
69. A Weston frequency meter is……
(a) moving coil instrument
(b) moving iron instrument
(c) dynamometer instrument
(d) none of the above
Ans: b
70. A Weston synchronoscope is a……
(a) moving coil instrument
(b) moving iron instrument
(c) dynamometer instrument
(d) none of the above
Ans: c
71. is an instrument which measures the insulation resistance of an electric circuit relative to earth and one another ……
(a) Tangent galvanometer
(b) Meggar
(c) Current transformer
(d) None of the above
Ans: b
72. The household energy meter is……
(a) an indicating instrument
(b) a recording instrument
(c) an integrating instrument
(d) none of the above
Ans: c
73. The pointer of an indicating instrument should be……
(a) very light
(b) very heavy
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
74. The chemical effect of current is used in……
(a) D.C. ammeter hour meter
(b) D.C. ammeter
(c) D.C. energy meter
(d) none of the above
Ans: a
75. In majority of instruments damping is provided by……
(a) fluid friction
(b) spring
(c) eddy currents
(d) all of the above
Ans: c
76. An ammeter is a……
(a) secondary instrument
(b) absolute instrument
(c) recording instrument
(d) integrating instrument
Ans: a
77. In a portable instrument, the controlling torque is provided by……
(a) spring
(b) gravity
(c) eddy currents
(d) all of the above
Ans: a
78. The disc of an instrument using eddy current damping should be of……
(a) conducting and magnetic material
(b) non-conducting and magnetic material
(c) conducting and non-magnetic material
(d) none of the above
Ans: c
79. The switch board instruments……
(a) should be mounted in vertical position
(b) should be mounted in horizontal position
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
80. The function of shunt in an ammeter is to……
(a) by pass the current
(b) increase the sensitivity of the ammeter
(c) increase the resistance of ammeter
(d) none of the above
Ans: a
81. In a low power factor wattmeter the compensating coil is connected……
(a) in series with current coil
(b) in parallel with current coil
(c) in series with pressure coil
(d) in parallel with pressure coil
Ans: c
82. In a 3-phase power measurement by two wattmeter method, both the watt meters had identical readings. The power factor of the load was……
(a) unity
(b) 0.8 lagging
(c) 0.8 leading
(d) zero
Ans: a
83. In a 3-phase power measurement by two wattmeter method the reading of one of the wattmeter was zero. The power factor of the load must be……
(a) unity
(b) 0.5
(c) 0.3
(d) zero
Ans: b
84. The adjustment of position of shading bands, in an energy meter is done to provide……
(a) friction compensation
(b) creep compensation
(c) braking torque
(d) none of the above
Ans: a
85. An ohmmeter is a……
(a) moving iron instrument
(b) moving coil instrument
(c) dynamometer instrument
(d) none of the above
Ans: b
86. When a capacitor was connected to the terminal of
ohmmeter, the pointer indicated a low resistance initially and then
slowly came to infinity position. This shows that
capacitor is……
(a) short-circuited
(b) all right
(c) faulty
Ans: b
87. For measuring a very high resistance we should use……
(a) Kelvin’s double bridge
(b) Wheat stone bridge
(c) Meggar
(d) None of the above
Ans: c
88. The electrical power to a meggar is provided by……
(a) battery
(b) permanent magnet D.C. generator
(c) AC. generator
(d) any of the above
Ans: b
89. In a meggar controlling torque is provided by……
(a) spring
(b) gravity
(c) coil
(d) eddy current
Ans: c
90. The operating voltage of a meggar is about……
(a) 6 V
(b) 12 V
(c) 40 V
(d) 100 V
Ans: d
91. The multiplier and the meter coil
in a voltmeter are in……
(a) series
(b) parallel
(c) series-parallel
(d) none of the above
Ans: a
92. A moving iron instrument can be
used for……
(a) D.C. only
(b) A.C. only
(c) both D.C. and A.C.
Ans: c
93. The scale of a rectifier instrument is……
(a) linear
(b) non-linear
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
94. For measuring current at high frequency we should
use……
(a) moving iron instrument
(b) electrostatic instrument
(c) thermocouple instrument
(d) none of the above
Ans: c
95. The resistance in the circuit of the moving coil of
a dynamometer wattmeter should be……
(a) almost zero
(b) low
(c) high
(d) none of the above
Ans: c
96. A dynamometer wattmeter can be used for……
(a) both D.C. and A.C.
(b) D.C. only
(c) A.C. only
(d) any of the above
Ans: a
97. An induction wattmeter can be used for……
(a) both D.C. and A.C.
(6) D.C. only
(c) A.C. only
(d) any of the above
Ans: b
98. The pressure coil of a wattmeter should be connected
on the supply side of the current coil when……
(a) load impedance is high
(b) load impedance is low
(c) supply voltage is low
(d) none of the above
Ans: a
99. In a low power factor wattmeter the pressure coil is
connected……
(a) to the supply side of the current coil
(b) to the load side of the current coil
(c) in any of the two meters at connection
(d) none of the above
Ans: b
100. An instrument transformer is used to extend the range of……
(a) induction instrument
(b) electrostatic instrument
(c) moving coil instrument
(d) any of the above
Ans: a
Top 100 MCQ Magnet
Top 100 MCQ Magnet For all competitive Exam. and others
1. A material which is slightly repelled by a magnetic field is known as……….
(a) ferromagnetic material
(b) diamagnetic material
(c) paramagnetic material
(d) conducting material
Ans: b
2. When an iron piece is placed in a magnetic field…..
(a) the magnetic lines of force will bend away from their usual paths in order to go away from the piece
(b) the magnetic lines of force will bend away from their usual paths in order to pass through the piece
(c) the magnetic field will not be affected
(d) the iron piece will break
Ans: b
3. Fleming’s left hand rule is used to find…..
(a) direction of magnetic field due to current carrying conductor
(b) direction of flux in a solenoid
(c) direction of force on a current carrying conductor in a magnetic field
(d) polarity of a magnetic pole
Ans: c
4. The ratio of intensity of magnetisation to the magnetisation force is known as…..
(a) flux density
(b) susceptibility
(c) relative permeability
(d) none of the above
Ans: b
5. Magnetising steel is normally difficult because…..
(a) it corrodes easily
(6) it has high permeability
(c) it has high specific gravity
(d) it has low permeability
Ans: d
6. The left hand rule correlates to…..
(a) current, induced e.m.f. and direction of force on a conductor
(b) magnetic field, electric field and direction of force on a conductor
(c) self induction, mutual induction and direction of force on a conductor
(d) current, magnetic field and direction of force on a conductor
Ans: d
7. The unit of relative permeability is…..
(a) henry/metre
(b) henry
(c) henry/sq. m
(d) it is dimensionless
Ans: d
8. A conductor of length L has current I passing through it, when it is placed parallel to a magnetic field. The force
experienced by the conductor will be…..
(a) zero
(b) BLI
(c) B2LI
(d) BLI2
Ans: a
9. The force between two long parallel conductors is inversely proportional to…..
(a) radius of conductors
(b) current in one conductor
(c) product of current in two conductors
(d) distance between the conductors
Ans: d
10. Materials subjected to rapid reversal of magnetism should have…..
(a) large area oiB-H loop
(b) high permeability and low hysteresis loss
(c) high co-ercivity and high retentivity
(d) high co-ercivity and low density
Ans: b
11. Indicate which of the following material does not retain magnetism permanently……
(a) Soft iron
(b) Stainless steel
(c) Hardened steel
(d) None of the above
Ans: a
12. Ferrites are materials……
(a) paramagnetic
(b) diamagnetic
(c) ferromagnetic
(d) none of the above
Ans: c
13. Air gap has_______eluctance as compared to iron or steel path
(a) little
(b) lower
(c) higher
(d) zero
Ans: b
14. The direction of magnetic lines of force is…..
(a) from south pole to north pole
(b) from north pole to south pole
(c) from one end of the magnet to another
(d) none of the above
Ans: b
15. Which of the following is a vector quantity ?
(a) Relative permeability
(b) Magnetic field intensity
(c) Flux density
(d) Magnetic potential
Ans: b
16. The two conductors of a transmission line carry equal current I in opposite directions. The force on each conductor is…..
(a) proportional to 7
(b) proportional to X
(c) proportional to distance between the conductors
(d) inversely proportional to I
Ans: b
17. Tesla is a unit of…..
(a) field strength
(b) inductance
(c) flux density
(d) flux
Ans: c
18. A permeable substance is one…..
(a) which is a good conductor
(6) which is a bad conductor
(c) which is a strong magnet
(d) through which the magnetic lines of force can pass very easily
Ans: d
19. The materials having low retentivity are suitable for making…..
(a) weak magnets
(b) temporary magnets
(c) permanent magnets
(d) none of the above
Ans: b
20. A magnetic field exists around…..
(a) iron
(b) copper
(c) aluminium
(d) moving charges
Ans: d
21. For which of the following materials the saturation value is the highest ?
(a) Ferromagnetic materials
(6) Paramagnetic materials
(c) Diamagnetic materials
(d) Ferrites
Ans: d
22. The magnetic materials exhibit the property of magnetisation because of…..
(a) orbital motion of electrons
(b) spin of electrons
(c) spin of nucleus
(d) either of these
(e) all of the above
Ans: c
23. For which of the following materials the net magnetic moment should be zero ?
(a) Diamagnetic materials
(b) Ferrimagnetic materials
(c) Antiferromagnetic materials
(d) Antiferromagnetic materials
Ans: c
24. The attraction capacity of electromagnet will increase if the…..
(a) core length increases i
(b) core area increases
(c) flux density decreases
(d) flux density increases
Ans: d
25. Which of the following statements is correct ?
(a) The conductivity of ferrites is better than ferromagnetic materials
(b) The conductivity of ferromagnetic materials is better than ferrites
(c) The conductivity of ferrites is very high
(d) The conductivity of ferrites is same as that of ferromagnetic materials
Ans: a
26. Temporary magnets are used in…..
(a) loud-speakers
(b) generators
(c) motors
(d) all of the above
Ans: d
27. Main causes of noisy solenoid are…..
(a) strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force
(b) uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
(c) both of above
(d) none of the above
Ans: c
28. Strength of an electromagnet can be increased by…..
(a) increasing the cross-sectional area
(b) increasing the number of turns
(c) increasing current supply
(d) all above methods
Ans:
29. Core of an electromagnet should have…..
(a) low coercivity
(6) high susceptibility
(c) both of the above
(d) none of the above
Ans: c
30. Magnetism of a magnet can be destroyed by…..
(a) heating
(b) hammering
(c) by inductive action of another magnet
(d) by all above methods
Ans: d
31. Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials……
(a) circular
(b) triangular
(c) rectangular
(d) none of the above
Ans: c
32. A rectangular magnet of magnetic moment M is cut into two piece of same length, the magnetic moment of each piece
will be…..
(a) M
(6) M/2
(c) 2 M
(d) M/4
Ans: b
33. A keeper is used to…..
(a) change the direction of magnetic lines
(b) amplify flux
(c) restore lost flux
(d) provide a closed path for flux
Ans: d
34. Magnetic moment is a…..
(a) pole strength
(6) universal constant
(c) scalar quantity
(d) vector quantity
Ans: d
35. The change of cross-sectional area of conductor in magnetic field will affect…..
(a) reluctance of conductor
(b) resistance of conductor
(c) (a) and (b) both in the same way
(d) none of the above
Ans: c
36. The unit of flux is the same as that of…..
(a) reluctance
(b) resistance
(c) permeance
(d) pole strength
Ans: d
37. Unit for quantity of electricity is…..
(a) ampere-hour
(b) watt
(c) joule
(d) coulomb
Ans: d
38. The Biot-savart’s law is a general modification of…..
(a) Kirchhoffs law
(b) Lenz’s law
(c) Ampere’s law
(d) Faraday’s laws
Ans: c
39. The most effective and quickest may of making a magnet from soft iron is by…..
(a) placing it inside a coil carrying current
(b) induction
(c) the use of permanent magnet
(d) rubbing with another magnet
Ans: a
40. The commonly used material for shielding or screening magnetism is…..
(a) copper
(b) aluminium
(c) soft iron
(d) brass
Ans: c
41. If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with
a velocity…..
(a) less than that of disc but in opposite direction
(b) equal to that of disc and in the same direction
(c) equal to that of disc and in the opposite direction
(d) less than that of disc and in the same direction
Ans: d
42. A permanent magnet…..
(a) attracts some substances and repels others
(b) attracts all paramagnetic substances and repels others
(c) attracts only ferromagnetic substances
(d) attracts ferromagnetic substances and repels all others
Ans: a
43. The retentivity (a property) of material is useful for the construction of…..
(a) permanent magnets
(b) transformers
(c) non-magnetic substances
(d) electromagnets
Ans: a
44. The relative permeability of materials is not constant……
(a) diamagnetic
(b) paramagnetic
(c) ferromagnetic
(d) insulating
Ans: c
45. The materials are a bit inferior conductors of magnetic flux than air……
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) dielectric
Ans: c
46. Magnetic moment is a…..
(a) pole strength
(6) universal constant
(c) scalar quantity
(d) vector quantity
Ans: d
47. The change of cross-sectional area of conductor in magnetic field will affect…..
(a) reluctance of conductor
(b) resistance of conductor
(c) (a) and (b) both in the same way
(d) none of the above
Ans: c
48. The uniform magnetic field is…..
(a) the field of a set of parallel conductors
(b) the field of a single conductor
(c) the field in which all lines of magnetic flux are parallel and equidistant
(d) none of the above
Ans: c
49. The magneto-motive force is…..
(a) the voltage across the two ends of exciting coil
(b) the flow of an electric current
(c) the sum of all currents embraced by one line of magnetic field
(d) the passage of magnetic field through an exciting coil
Ans: c
50. What will be the current passing through the ring shaped air cored coil when number of turns is 800 and ampere turns
are 3200 ?
(a) 2
(b) 4
(c) 6
(d) 8
Ans: b
51. What will be the magnetic potential difference across the air gap of 2 cm length in magnetic field of 200 AT/m ?
(a) 2 AT
(b) 4 AT
(c) 6 AT
(d) 10 AT
Ans: b
52. Which of the following statements is correct ?
(a) The magnetic flux inside an exciting coil is lower than its outside surface
(b) The magnetic flux inside an exciting coil is zero
(c) The magnetic flux inside the exciting coil is greater than its outside surface
(d) The magnetic flux inside the exciting coil is same as on its outside surface
Ans: d
53. The magnetic reluctance of a material…..
(a) decreases with increasing cross sectional area of material
(6) increases with increasing cross-sectional area of material
(c) does not vary with increasing cross-sectional area of material
(d) any of the above
Ans: a
54. The initial permeability of an iron rod is…..
(a) the highest permeability of the iron rod
(b) the lowest permeability of the iron rod
(c) the permeability at the end of the iron rod
(d) the permeability almost in non-magnetised state
Ans: d
55. How does the magnetic compass needle behave in a magnetic field ?
(a) It assures a position right angle to magnetic field
(b) It starts rotating
(c) It assures a position which follows a line of magnetic flux
(d) None of the above
Ans: c
56. In a simple magnetic field the strength of magnet flux…..
(a) is constant and has same value in energy part of the magnetic field
(6) increases continuously from initial value to final value
(c) decreases continuously from initial value to final value
(d) first increases and then decreases till it becomes zero
Ans: d
57. The stray line of magnetic flux is defined as…..
(a) a line vertical to the flux lines
(b) the mean length of a ring shaped coil
(c) a line of magnetic flux in a non-uniform field
(d) a line of magnetic flux which does not follow the designed path
Ans: d
58. The bar magnet has…..
(a) the dipole moment
(b) monopole moment
(c) (a) and (b) both
(d) none of the above
Ans: a
59. Which of the following materials are diamagnetic ?
(a) Silver
(b) Copper
(c) Silver and copper
(d) Iron
Ans: c
60. Which of the following type of materials are not very important for engineering applications ?
(a) Ferromagnetic
(b) Paramagnetic
(c) Diamagnetic
(d) None of the above
Ans: c
61. The susceptibility of paramagnetic materials generally lies between…
(a) KT3 and 1CT6
(b) 1CT3 and 1CT7
(c) KT4 and KT8
(d) 10″2 and KT5
Ans: a
62. The main constituent of permalloy is…..
(a) cobalt
(b) chromium
(c) nickel
(d) tungsten
Ans: c
63. The use of permanent magnets is. not made in…..
(a) magnetoes
(b) energy meters
(c) transformers
(d) loud-speakers
Ans: c
64. Paramagnetic materials have relative permeability…..
(a) slightly less than unity
(b) equal to unity
(c) slightly more than unity
(d) equal to that ferromagnetic mate rials
Ans: c
65. Degaussing is the process of…..
(a) removal of magnetic impurities
(b) removing gases from the materials
(c) remagnetising metallic parts
(d) demagnetising metallic parts
Ans:d
66. Substances which have permeability less than the permeability of free space are known as…..
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) bipolar
Ans: c
67 Two infinitely long parallel conductors in vacuum any separated 1 meter between centers >then a current of 1 ampere
flows the. uk each conductor, produce on each other a force of…..
(a) 2 x 1(T2 N/m)
(b) 2 x KT3 N/m
(c) 2 x 10″5 N/m
(d) 2x 1(T7 N/m)
Ans: d
68. In the left hand rule, forefinger always represents…..
(a) voltage
(b) current
(c) magnetic field
(d) direction of force on the conductor
Ans: c
69. Which of the following is a ferromagnetic material ?
(a) Tungsten
(b) Aluminium
(c) Copper
(d) Nickel
Ans: d
70. Ferrites are a sub-group of…..
(a) non-magnetic materials
(b) ferro-magnetic materials
(c) paramagnetic materials
(d) dia-magnetic materials
Ans: b
71. Gilbert is a unit of…..
(a) electromotive force
(b) magnetomotive force
(c) conductance
(d) permittivity
Ans: b
72. When a magnet is in motion relative to a coil the induced e.m.f. does not depend upon…..
(a) resistance of the coil
(b) motion of the magnet
(c) number of turns of the coil
(d) pole strength of the magnet
Ans: a
73. One maxwell is equal to…..
(a) 10 webers
(b) 10 webers
(c) 10 webers
(d) 10 webers
Ans: d
74. When two ends of a circular uniform wire are joined to the terminals of a battery, the field at the center of the circle…..
(a) will be zero
(b) will be infinite
(c) will depend on the amount of e.m.f. applied
(d) will depend on the radius of the circle
Ans: d
75. Susceptibility is positive for…..
(a) non-magnetic substances
(b) diamagnetic substances
(c) ferromagnetic substances
(d) none of the above
Ans: c
76. Two long parallel conductors carry 100 A. If the conductors are separated by 20 mm, the force per meter of length of
each conductor will be…..
(a) 100 N
(b) 10 N
(c) 1 N
(d) 0.1 N
Ans: d
77. A 300 mm long conductor is carrying a current of 10 A and is situated at right angles to a magnetic field having a flux density of 0.8 T ; the force on the conductor will be…..
(a) 240 N
(6) 24 N
(c) 2.4 N
(d) 0.24 N
Ans: c
78. A 200 turn coil having an axial length of 30 mm and a radius of 10 mm is pivoted in a magnetic field having a flux density of 0.8 T. If the coil carries a current of 0.5 A, the torque acting on the coil will be…..
(a) 8 N-m
(b) 0.48 N-m
(e) 0.048 N-m
(d) 0.0048 N-m
[Hint. Torque = 2BIlNr N-m]
Ans: c
79. The electromagnet has 50 turns and a current of 1A flows through the coil. If the length of the magnet circuit is 200 mm,
what is the magnetic field strength ?
(a) 2500 AT/m
(b) 250 AT/m
(c) 25 AT/m
(d) 2.5 AT/m
Ans: b
80. What is the magnitude and the direction of force per 1.1m length of a pair of conductors of a direct current line carrying
10 amperes and spaced 100 mm apart ?
(a) 22 x 10″8 N
(b) 22 x 10″7 N
(c) 22 x 10-6 N
(d) 22 x 10″5 N
Ans: d
81. A square cross-sectional magnet has a pole strength of 1 x 10 Wb and cross sectional area of 20 mm x 20 mm. What is
the strength at a distance of 100 mm from the unit pole in air ?
(a) 63.38 N/Wb
(b) 633.8 N/Wb
(c) 6338 N/Wb
(d) 63380 N/Wb
Ans: c
82. The working of a meter is based on the use of a permanent magnet. In order to protect the meter functioning from stray
magnetic fields…..
(a) meter is surrounded by strong magnetic fields
(b) a soft iron shielding is used
(c) a plastic shielding is provided
(d) a shielding of anon-magnetic material is used
Ans: b
83. Reciprocal of permeability is…..
(a) reluctivity
(b) susceptibility
(c) permittivity
(d) conductance
Ans: a
85. The relative permeability is less than unity is case of…..
(a) ferromagnetic materials
(b) ferrites
(c) non-ferrous materials
(d) diamagnetic materials
Ans: d
86. Which of the following is the unit of magnetic flux density ?
(a) weber
(b) lumens
(c) tesla
(d) none of the above
Ans: c
87. The magnetism left in the iron after exciting field has been removed is known as…..
(a) permeance
(b) residual magnetism
(c) susceptance
(d) reluctance
Ans: b
88. Which of the following is not a unit of flux?
(a) Maxwell
(b) Telsa
(c) Weber
(d) All of the above
Ans: b
89. Which of the following is expected to have the maximum permeability ?
(a) Brass
(b) Copper
(c) Zinc
(d) Ebonite
Ans: d
90. One telsa is equal to…..
(a) 1 Wb/mm2
(b) 1 Wb/m
(c) 1 Wb/m2
(d) 1 mWb/m2
Ans: c
91. Out of the following statements, concerning an electric field, which statement is not true ?
(a) The electric intensity is a vector quantity
(b) The electric field intensity at a point is numerically equal to the force exerted upon a charge placed at that point
(c) An electric field is defined as a point in space at which an electric charge would experience a force
(d) Unit field intensity in the exertion of a force of one newton on a charge of one coulomb
Ans: b
92. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
(a) resistance
(b) resistivity
(c) conductivity
(d) conductance
Ans: c
93. Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it…..
(a) lowers their power efficiency
(b) increases their cost of manufacture
(c) leads to their increased weight
(d) produces fringing
Ans: a
94. Relative permeability of vacuum is…..
(a) 1
(b) 1 H/m
(c) 1/4JI
(d) 4n x 10-‘ H/m
Ans: a
96. Permanent magnets are normally made of…..
(a) alnico alloys
(b) aluminium
(c) cast iron
(d) wrought iron
Ans: a
97. Those magnetic materials are best suited for making armature and transformer cores which have ___ permeability
and _____ hysteresis loss.
(a) high, high
(b) low, high
(c) high, low
(d) low, low
Ans: c
98. The rate of rise of current through an inductive coil is maximum…..
(a) at 63.2% of its maximum steady value
(b) at the start of the current flow
(c) after one time constant
(d) near the final maximum value of current
Ans: b
99. When both the inductance and resistance of a coil are doubled the value of…..
(a) time constant remains unchanged
(b) initial rate of rise of current is doubled
(c) final steady current is doubled
(d) time constant is halved
Ans: a
100. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V
is_____ Vs
(a) 50
(b) 20
(c) 0.05
(d) 500
Ans: b
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1. 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
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2. 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
3. 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
4. The r.m.s. value and mean value is the same in the case of
(a) triangular wave
(b) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c
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5. 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
6. 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
7. 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
8. 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
9. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c
10. 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
11. 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
12. 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
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13. 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
14. 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
15. 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
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16. 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
17. 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
18. 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
19. The form factor is the ratio of
(a) peak value to r.m.s. value
(b) r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above
Ans: b
20. 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
21. 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
22. Skin effect occurs when a conductor carries current at_____ frequencies.
(a) very low
(b) low
(c) medium
(d) high
Ans: d
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23. At ______ frequencies the parallel R-L circuit behaves as purely resistive.
(a) low
(b) very low
(c) high
(d) very high
Ans: d
24. 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
25. 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
26. 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
27. 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
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28. The frequency of domestic power supply in India is
(a) 200 Hz
(b) 100 Hz
(c) 60 Hz
(d) 50 Hz
Ans: d
29. 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
30. 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
31. Ohm is unit of all of the following except
(a) inductive reactance
(b) capacitive reactance
(c) resistance
(d) capacitance
Ans: d
32. The series and parallel resonance on L-C circuit’ differs in that
(a) series resistance needs a low-resistance source 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
33. The phosphors 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
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34. 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
35. 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
36. 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
37. 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 increases the total value
(d) oppose sudden changes in voltage
Ans: a
38. 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
39. A phasors
(a) a line which represents the magnitude 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
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40. 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
41. 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, Land C
Ans: a
42. 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
43. 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
44. 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
45. The time constant of a series R-C circuit is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c
47. 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
48. 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
49. 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
50. Which of the following circuit component opposes the change in the circuit voltage ?
(a) Inductance
(b) Capacitance
(c) Conductance
(d) Resistance
Ans: b
51. 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
52. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d
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53. Pure inductive circuit takes power from the A.C. line when
(a) applied voltage decreases but current increases
(b) applied voltage increases but current decreases
(c) both applied voltage and current increase
(d) both applied voltage and current decrease
Ans: a
54. 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
55. 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
56. 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 resistance
(c) increases with the increase of capacitance and decrease of resistance
(d) increase with increase of capacitance and increase of resistance
Ans: d
57. 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
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58. The time constant of a series R-C circuit is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c
59. 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
60. 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
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61. 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
62. 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
63. 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
64. 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
65. 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
66. 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
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67. 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
68. The ratio of active power to apparent power is known as factor.
(a) demand
(b) load
(c) power
(d) form
Ans: c
69. 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
70. 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
71. 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
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72. The purpose of a parallel circuit resonance is to magnify
(a) current
(b) voltage
(c) power
(d) frequency
Ans: b
73. 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
74. 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
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75. 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
76. 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
77. In a series resonant circuit, the impedance of the circuit is
(a) minimum
(b) maximum
(c) zero
(d) none of the above
Ans: a
78. Power factor of an electrical circuit is equal to
(a) R/Z
(b) cosine of phase angle difference be-tween current and voltage
(c) kW/kVA
(d) ratio of useful current to total cur¬rent Iw/I
(e) all above
Ans: e
79. 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
80. 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
81. Capacitors for power factor correction are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d
82. 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
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83. 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
84. 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
85. In a loss-free R-L-C circuit the transient current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c
86 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
87. 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
88. 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
89. 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
90. 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
91. 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
92. 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
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93. 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
94. 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
95. 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
96. 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
97. 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
98. 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
99. 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 power
(d) actual power is more than its reactive power
Ans: c
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100. Power factor of the following circuit will be zero
(a) resistance
(b) inductance
(c) capacitance
(d) both (b) and (c)
Ans: d
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1. In a shaded pole motor, the shading coil usually consist of
(a) a single turn of heavy wire which is in parallel with running winding
(b) a single turn of heavy copper wire which is short-circuited and carries only induced current
(c) a multilayer fine gauge copper wire in parallel with running winding
(d) none of the above
Ans :b
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2. In a shaded pole single-phase motor, the revolving field is produced by the use of
(a) inductor
(b) capacitor
(c) resistor
(d) shading coils
Ans :d
3. A centrifugal switch is used to dis- connect ‘starting winding when motor has
(a) run for about 1 minute
(b) run for about 5 minutes
(c) picked up about 50 to 70 per cent of rated speed
(d) picked up about 10 to 25 per cent of rated speed
Ans :c
4. If a particular application needs high speed and high starting torque, then which of the following motor will be
preferred ?
(a) Universal motor
(b) Shaded pole type motor
(c) Capacitor start motor
(d) Capacitor start and run motor
Ans :a
5. The value of starting capacitor of a fractional horse power motor will be
(a) 100 uF
(6) 200 uF
(c) 300 uF
(d) 400 uF
Ans :c
6. In repulsion motor direction of rotation of motor
(a) is opposite to that of brush shift
(b) is the same as that of brush shift
(c) is independent of brush shift
Ans :b
7. In a single phase motor the centrifugal switch
(a) disconnects auxiliary winding of the motor
(b) disconnects main winding of the motor
(c) reconnects the main winding the motor
(d) reconnects the auxiliary winding of the motor
Ans :a
8. The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the
ground will be
(a) at the end connections
(b) at the end terminals
(c) anywhere on the winding inside a slot
(d) at the slot edge where coil enters or comes out of the slot
Ans :d
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9. A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of
equivalent reactance value. It will
(a) start and then stop
(b) start and run slowly
(c) start and run at rated speed
(d) not start at all
Ans: d
10. Which of the following motors is used in mixtures ?
(a) Repulsion motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor
Ans: d
11. Which of the following motors is inherently self starting ?
(a) Split motor
(b) Shaded-pole motor
(c) Reluctance motor (d) None of these
Ans :b
12. In a capacitor start motor, the phase displacement between starting and running winding can be nearly
(a) 10°
(b) 30°
(c) 60°
(d) 90°
Ans: d
13. In a split phase motor
(a) the starting winding is connected through a centrifugal switch
(b) the running winding is connected through a centrifugal switch
(c) both starting and running windings are connected through a centrifugal switch
(d) centrifugal switch is used to control supply voltage
Ans: a
14. The rotor developed by a single-phase motor at starting is
(a) more than. the rated torque
(b) rated torque
(c) less than the rated torque
(d) zero
Ans: d
15. Which of the following motor will give relatively high starting torque ?
(a) Capacitor start motor
(b) Capacitor run motor (c) Split phase motor
(d) Shaded pole motor
Ans :a
16. Which of the following motor will have relatively higher power factor ?
(a) Capacitor run motor
(b) Shaded pole motor
(c) Capacitor start motor
(d) Split phase motor
Ans :a 17. In a split phase motor, the running winding should have
(a) high resistance and low inductance
(b) low resistance and high inductance
(c) high resistance as well as high inductance
(d) low resistance as well as low inductance
Ans :b
18. If the capacitor of a single-phase motor is short-circuited
(a) the motor will not start
(b) the motor will run
(c) the motor will run in reverse direction
(d) the motor will run in the same direction at reduced r.p.m.
Ans :a
19. In capacitor start single-phase motors
(a) current in the starting winding leads the voltage
(b) current in the starting winding lags the voltage
(c) current in the starting winding is in phase with voltage in running winding
(d) none of the above
Ans :a
20. In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to
(a) improve power factor
(b) increase overload capacity
(c) reduce fluctuations in torque
(d) to improve torque
Ans :a 21. Centrifugal switch disconnects the auxiliary winding of the motor at about ____ percent of synchronous speed
(a) 30 to 40
(b) 70 to 80
(c) 80 to 90
(d) 100
Ans :b
22. Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a
(a) magnetic relay
(b) thermal relay
(c) centrifugal switch
(d) none of the above
Ans :a
23. If a single phase induction motor runs slower than normal, the most likely defect is
(a) worn bearings
(b) short-circuit in the winding
(c) open-circuit in the winding
(d) none of the above
Ans :a
24. Which of the following motors is used in tape-recorders ?
(a) Hysteresis motor
(b) Reluctance motor
(c) Capacitor-run motor
(d) Universal motor
Ans :a
25. Which of the following statements regarding reluctance-start motor is incorrect ?
(a) It is similar to reluctance motor
(b) It is basically an induction motor and not a synchronous one
(c) So far as its basic working principle is concerned, it is similar to shaded pole motor
(d) the air-gap between rotor and salient poles is non- uniform
Ans :a
26. To reverse the direction of rotation of capacitor start motor while it is running we should
(a) disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary
winding
(b) disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding
(c) reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding
to the supply
(d) reverse the direction of connections of the auxiliary winding and immediately connect it to supply
Ans :a
28. In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will
(a) become unstable
(b) draw excessive armature current and may burn out
(c) fall out of synchronism and come to stand still
(d) run as induction motor
Ans :d
29. Which of the following motors has two separate windings on the motor ?
(a) Repulsion motor
(b) Repulsion induction motor
(c) Repulsion start induction run motor
(d) None of the above
Ans :b
30. A shaded pole motor does not possess
(a) centrifugal switch
(b) capacitor
(c) commutator
(d) all of the above
Ans :d
31. In a A.C. series motor armature coils are usually connected to commutator
(a) through resistance
(b) through reactance’s
(c) through capacitors
(d) solidly
Ans :a
32. Which of the following statements regarding a reluctance motor is incorrect ?
(a) It cannot be reversed, ordinarily
(b) It requires no D.C. field excitation for its operation
(c) It is nothing else but a single-phase, salient pole synchronous-induction motor
(d) Its squirrel cage-rotor is of unsymmetrical magnetic construction in order to vary reluctance path between stator and rotor
Ans :a
33. A universal motor is one which
(a) can be operated either on D.C. or A.C. supply at approximately the same speed and output
(b) can be marketed internationally
(c) runs at dangerously high speed on no-load
Ans :a
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34. A repulsion motor is equipped with
(a) slip rings
(b) commutator
(c) both (a) and (b)
(d) none of the above
Ans :b
35. The capacitors used in single-phase capacitor motors have no
(a) voltage rating
(b) dielectric medium
(c) polarity marking
(d) definite value
Ans :c
36. If a D.C. series motor is operated on A.C. supply, it will
(a) spark excessively
(b) have poor efficiency
(c) have poor power factor
(d) all of the above
Ans :d
37. Which of the following statements regarding two value capacitor motor is incorrect ?
(a) It is a reversing motor
(b) It is preferred to permanent-split single-value capacitor motor where frequent reversals are required
(c) It has low starting as well as rushing currents
(d) It has high starting torque
Ans :b
38. Two-value capacitor motor finds increased application as compressor motor in small home air-conditioners
because
(a) it is comparatively cheaper
(b) it has almost non-destructible capacitor
(c) it has low starting as well as running currents at relatively high power factor
(d) it is quiet in operation
Ans :c
39. If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then
(a) motor will not come up to speed
(b) motor will not carry the load
(c) current drawn by the motor will be excessively high
(d) electrolytic capacitor will, in all probability, suffer break down
Ans :d
40. In a universal motor, the most common cause of brush sparking is
(a) open armature winding
(b) shorted armature winding
(c) shorted field winding”
(d) high commutator mica
(e) all of the above
Ans :e
41. If starting winding of a single-phase induction motor is left in the circuit, it will
(a) run faster
(b) spark at light loads
(c) draw excessive current and overheat
(d) run slower
Ans :c
42. Most of the fractional horsepower motors have either
(a) hard and annealed bearings
(b) ball or roller bearings
(c) soft and porous bearings
(d) plain or sleeve bearings
Ans :d
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43. A reluctance motor
(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above
Ans :d
44. In a hysteresis motor, the rotor must have
(a) retentivity
(b) resistivity
(c) susceptibility
(d) none of the above
Ans :a
45. The rotor of a hysteresis motor is made of
(a) aluminium
(b) cast iron
(c) chrome steel
(d) copper
Ans :c
46. The electric motor used in portable drills is
(a) capacitor run motor
(b) hysteresis motor
(c) universal motor
(d) repulsion motor
Ans :c
47. Which of the following applications always have some load whenever switched on ?
(a) Vacuum cleaners
(b) Fan motors
(c) Pistol drills
(d) All of the above
Ans :c
48. The wattage of motor for driving domestic sewing machine will be around
(a) 100 to 150 W
(b) 40 to 75 W
(c) 10 to 30 W
(d) 5 to 10 W
Ans :a
49. Which of the following single-phase motors has relatively poor starting torque ?
(a) Universal motor
(b) Repulsion motor
(c) Capacitor motor
(d) All single phase motors have zero starting torque
Ans :c
50. Which type of load is offered by cranes and hoists ?
(a) Gradually varying load
(b) Non-reversing, no-load start
(c) Reversing, light start
(d) Reversing, heavy start
Ans :d
51. The speed of a universal motor is generally reduced by using
(a) gear trains
(b) V-belts
(c) brakes
(d) chains
Ans :a
52. Which of the following motors can be used for unity power factor ?
(a) Capacitor run motor
(b) Shaded pole motor
(c) Hysteresis motor
(d) Schrage motor
Ans :d
53. When a D.C. series motor is connected to A.C. supply, the power factor will be low because of
(a) high inductance of field and armature circuits
(b) induced current in rotor due to variations of flux
(c) fine copper wire winding
(d) none of the above
Ans :a
54. The direction of rotation of universal motor can be reversed the by reversing the flow of current through
(a) armature winding
(b) field winding
(c) either armature winding or field winding
(d) none of the above
Ans :c
55. In which single-phase motor, the rotor has no teeth or winding ?
(a) Split phase motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor
Ans :c
56. Which motor is normally free from mechanical and magnetic vibrations ?
(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor
(d) Shaded pole motor
Ans :c
57. As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for
(a) fans
(b) blowers
(c) sound equipment
(d) mixer grinders
Ans :c
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58. The speed control of universal motor used for sewing machines is by
(a) friction
(b) varying the resistance
(c) tapping the field
(d) centrifugal mechanism
Ans :b
59. Torque developed by a single phase induction motor at starting is
(a) pulsating
(b) uniform
(c) none of the above
(d) nil
Ans :d
60. In split phase motor main winding is of
(a) thin wire placed at the top of the slots
(b) thin wire placed at the bottom of the slots
(c) thick wire placed at the bottom of the slots
(d) thick wire placed at the top of the” slots
Ans :c
61. In repulsion motor, maximum torque is developed when
(a) brush axis is at 45° electrical to the field axis
(b) brush axis coincides with the field axis
(c) brush axis is at 90° electrical to the field axis
(d) none of the above
Ans :a
62. If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in
(a) damage to the starting winding
(b) damage to the centrifugal switch
(c) overloading of running winding
(d) none of the above
Ans :a
63. Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.
(a) shunt motor
(b) series motor
(c) compound motor
(d) separately excited motor
Ans :c
64. In a ceiling fan employing capacitor run motor
(a) secondary winding surrounds the primary winding
(b) primary winding surrounds the secondary winding
(c) both are usual arrangements
(d) none of the above
Ans :a
65. The shaded pole motor is used for
(a) high starting torque
(b) low starting torque
(c) medium starting torque
(d) very high starting torque
Ans :b
66. The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it
(a) improves the efficiency
(b) helps the rotor teeth to remain under the stator teeth
(c) helps in reducing the tendency of the rotor teeth to remain under the stator teeth
(d) improves the power factor
Ans :c
67. The speed/load characteristics of a universal motor is same as that of
(a) A.C. motor
(b) D.C. shunt motor
(c) D.C. series motor
(d) none of the above
Ans :c
68. The purpose of stator winding in the compensated repulsion motor is to
(a) provide mechanical balance
(b) improve power factor and provide better speed regulation
(c) prevent hunting in the motor
(d) eliminate armature reaction
Ans :b
69. Which of the following motors is used for unity power factor ?
(a) Hysteresis motor
(b) Schrage motor
(c) Universal motor
(d) Reluctance motor
Ans :b
70. The motor used for the compressors is
(a) d.c. series motor
(b) shaded pole motor
(c) capacitor-start capacitor-run motor
(d) reluctance motor
Ans :c
71. Which of the following motors is used in a situation where load increases with speed ?
(a) Induction motor
(b) Three-phase series motor
(c) Schrage motor
(d) Hysteresis motor
Ans :b
72. In repulsion motor, zero torque is developed when
(a) brush axis is 45° electrical to field axis
(b) brush axis coincides with the field axis
(c) brush axis is 90° electrical to field axis
(d) both (b) and (c)
Ans :d
73. The direction of rotation of an hysteresis motor is determined by
(a) interchanging the supply leads
(b) position of shaded pole with respect to main pole
(c) retentivity of the rotor material
(d) none of these
Ans :b
74. Burning out of windings is due to
(a) short circuited capacitor
(b) capacitor value hiving changed
(c) open circuiting of capacitor
(d) none of the above
Ans :a
75. Direction of rotation of a split phase motor can be reversed by reversing the connection of
(a) running winding only
(b) starting winding only
(c) either (a) or (b)
(d) both (a) and (b)
Ans :c
76. Short-circuiter is used in
(a) repulsion induction motor
(b) repulsion motor
(c) repulsion start induction run motor
(d) none of the above
Ans :c
77. The range of efficiency for shaded pole motors is
(a) 95% to 99%
(b) 80% to 90%
(c) 50% to 75%
(d) 5% to 35%
Ans :d
78. In a capacitor start single-phase motor, when capacitor is replaced by a resistance
(a) torque will increase
(b) the motor will consume less power
(c) motor will run in reverse direction
(d) motor will continue to run in same direction
Ans :d
79. The power factor of a single-phase induction motor is usually
(a) lagging
(b) always leading
(c) unity
(d) unity to 0.8 leading
Ans :a
80. A shaded pole motor can be used for
(a) toys
(b) hair dryers
(c) circulators
(d) any of the above
Ans :d
81. A hysteresis motor works on the principle of
(a) hysteresis loss
(b) magnetisation of rotor
(c) eddy current loss
(d) electromagnetic induction
Ans :a
82. Which of the following motor will give the highest starting torque ?
(a) D.C. shunt motor
(b) Schrage motor
(c) Repulsion start and induction run motor
(d) Universal motor
Ans :b
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83. Which of the following motors will operate at high power factor ?
(a) Shaped pole motor
(b) Split phase motor
(c) Capacitor start motor
(d) Capacitor run motor
Ans :d
84. In a two value capacitor motor, the capacitor used for running purposes is
(a) air capacitor
(b) paper spaced oil filled type
(c) ceramic type
(d) a.c. electrolytic type
Ans :b
85. Which of the following motors can be run on AC. as well as D.C. supply ?
(a) Universal motor
(b) Repulsion motor
(c) Synchronous motor
(d) Reluctance motor
Ans :a
86. In A.C. series motor compensating winding is employed to
(a) reduce the effects of armature reaction
(b) increase the torque
(c) reduce sparking at the brushes
(d) none of the above
Ans :c
87. Which of the following single-phase induction motors is generally used in time phonographs ?
(a) Resistance start
(b) Capacitor start capacitor run
(c) Shaded pole
(d) Universal
Ans :c
88. Which of the following motors has highest starting torque ?
(a) Repulsion motor
(b) Shaped pole motor
(c) Capacitor-start motor
(d) Split-phase motor
Ans :c
89. The repulsion-start induction-run motor is used because of
(a) good power factor
(b) high efficiency
(c) minimum cost
(d) high starting torque
Ans :d
90. In case of a shaded pole motor the direction of rotation of the motor is
(a) from main pole to shaded pole
(b) from shaded pole to main pole
(c) either of the above depending on voltage
(d) either of the above depending on power factor
Ans :a
91. In case of high speed universal motor which of the following needs more attention ?
(a) End play
(b) Air gap
(c) Insulation in rotor
(d) Balancing of rotor
Ans :d
92. The wattage rating for a ceiling fan motor will be in the range
(a) 200 to 250 W
(b) 250 to 500 W
(c) 50 to 150 W
(d) 10 to 20 W
Ans :c
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93. For which of the applications a reluctance motor is preferred ?
(a) Electric shavers
(b) Refrigerators
(c) Signaling and timing devices
(d) Lifts and hoists
Ans :c
94. The motor used on small lathes is usually
(a) universal motor
(b) D.C. shunt motor
(c) single-phase capacitor run motor
(d) 3-phase synchronous motor
Ans :c
95. Which of the following motors is preferred for tape-recorders ?
(a) Shaded pole motor
(b) Hysteresis motor
(c) Two value capacitor motor
(d) Universal motor
Ans :b
96. A single-phase induction motor is
(a) inherently self-starting with high torque
(b) inherently self-starting with low torque
(c) inherently non-self-starting with low torque
(d) inherently non-self-starting with high torque
Ans :c
97. A Schrage motor can run on
(a) zero slip
(b) negative slip
(c) positive slip
(d) all of the above
Ans :d
98. A universal motor can run on
(a) A.C. only
(b) D.C. only
(c) either A.C. or D.C.
(d) none of the above
Ans :c
99. Which of the following single-phase motors is suitable for timing and control purposes ?
(a) Reluctance motor
(b) Series motor
(c) Repulsion motor
(d) Universal motor
Ans :a
100. Single phase induction motor usually operates on
(a) 0.6 power factor lagging
(b) 0.8 power factor lagging
(c) 0.8 power factor leading
(d) unity power factor
Ans :a
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