Category: Electrical Engineering Multiple Choice Questions

Current Electricity Multiple Choice Questions

1. The S.I. unit of power is
A. Henry
B. coulomb
C. watt
D. watt-hour
Answer: C

2. Electric pressure is also called
A. resistance
B. power
C. voltage
D. energy
Answer: C

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

4. Out of the following which is not a poor conductor ?
A. Cast iron
B. Copper
C. Carbon
D. Tungsten
Answer: B

5. Out of the following which is an insulating material ?
A. Copper
B. Gold
C. Silver
D. Paper
Answer: D

6. The property of a conductor due to which it passes current is called
A. resistance
B. reluctance
C. conductance
D. inductance
Answer: C

7. Conductance is reciprocal of
A. resistance
B. inductance
C. reluctance
D. capacitance
Answer: A

8. The resistance of a conductor varies inversely as
A. length
B. area of cross-section
C. temperature
D. resistivity
Answer: B

9. With rise in temperature the resistance of pure metals
A. increases
B. decreases
C. first increases and then decreases
D. remains constant
Answer: A

10. With rise in temperature the resistance of semi-conductors
A. decreases
B. increases
C. first increases and then decreases
D. remains constant
Answer: A

11. The resistance of a copper wire 200 m long is 21 Q. If its thickness (diameter) is 0.44 mm, its specific resistance is around
A. 1.2 x 10~8 Q-m
B. 1.4 x 10~8 Q-m
C. 1.6 x 10″”8 Q-m
D. 1.8 x 10″8 Q-m
Answer: C

12. Three resistances of 10 ohms, 15 ohms and 30 ohms are connected in parallel. The total resistance of the combination is
A. 5 ohms
B. 10 ohms
C. 15 ohms
D. 55 ohms
Answer: A

13. An instrument which detects electric current is known as
A. voltmeter
B. rheostat
C. wattmeter
D. galvanometer
Answer: D

14. In a circuit a 33 Q resistor carries a current of 2 A. The voltage across the resistor is
A. 33 V
B. 66 v
C. 80 V
D. 132 V
Answer: B

15. A light bulb draws 300 mA when the voltage across it is 240 V. The resistance of the light bulb is
A. 400 Q
B. 600 Q
C. 800 Q
D. 1000 Q
Answer: C

16. The resistance of a parallel circuit consisting of two branches is 12 ohms. If the resistance of one branch is 18 ohms, what is the resistance of the other ?
A. 18 Q
B. 36 Q
C. 48 Q
D. 64 Q
Answer: B

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

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

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

20. Which of the following material has nearly zero temperature co-efficient of resistance?
A. Manganin
B. Porcelain
C. Carbon
D. Copper
Answer: A

21. You have to replace 1500 Q resistor in radio. You have no 1500 Q resistor but have several 1000 Q ones which you would connect
A. two in parallel
B. two in parallel and one in series
C. three in parallel
D. three in series
Answer: B

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

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

24. Which of the following materials has a negative temperature co-efficient of resistance?
A. Copper
B. Aluminum
C. Carbon
D. Brass
Answer: C

25. Ohm’s law is not applicable to
A. vacuum tubes
B. carbon resistors
C. high voltage circuits
D. circuits with low current densities
Answer: A

26. Which is the best conductor of electricity ?
A. Iron
B. Silver
C. Copper
D. Carbon
Answer: B

27. For which of the following ‘ampere second’ could be the unit ?
A. Reluctance
B. Charge
C. Power
D. Energy
Answer: B

28. All of the following are equivalent to watt except
A. (amperes) ohm
B. joules/sec.
C. amperes x volts
D. amperes/volt
Answer: D

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

30. Which one of the following does not have negative temperature co-efficient ?
A. Aluminium
B. Paper
C. Rubber
D. Mica
Answer: A

31. Varistors are
A. insulators
B. non-linear resistors
C. carbon resistors
D. resistors with zero temperature coefficient
Answer: B

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

33. The rating of a fuse wire is always expressed in
A. ampere-hours
B. ampere-volts
C. kWh
D. amperes
Answer: D

34. The minimum charge on an ion is
A. equal to the atomic number of the atom
B. equal to the charge of an electron
C. equal to the charge of the number of electrons in an atom (#) zero
Answer: B

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

36. The filament of an electric bulb is made of
A. carbon
B. aluminium
C. tungsten
D. nickel
Answer: C

37. A 3 Q resistor having 2 A current will dissipate the power of
A. 2 watts
B. 4 watts
C. 6 watts
D. 8 watts
Answer: C

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

39. The resistance of a few meters of wire conductor in closed electrical circuit is
A. practically zero
B. low
C. high
D. very high
Answer: A

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

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

42. Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns open
A. there will be heavy current in the main line
B. rest of the two bulbs will not light
C. all three bulbs will light
D. the other two bulbs will light
Answer: D

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

44. Two resistances Rl and Ri are connected in series across the voltage source where Rl>Ri. The largest drop will be across
A. Rl
B. Ri
C. either Rl or Ri
D. none of them
Answer: A

45. What will be energy used by the battery if the battery has to drive 6.28 x 1018 electrons with potential difference of 20 V across the terminal ?
A. 5 joules
B. 10 joules
C. 15 joules
D. 20 joules
Ans:

46. A closed switch has a resistance of
A. zero
B. about 50 ohms
C. about 500 ohms
D. infinity
Answer: A

47. The hot resistance of the bulb’s filament is higher than its cold resistance because the temperature co-efficient of the filament is
A. zero
B. negative
C. positive
D. about 2 ohms per degree
Answer: C

48. Heat in a conductor is produced on the passage of electric current due to
A. reactance
B. capacitance
C. impedance
D. resistance
Ans:

49. The insulation on a current carrying conductor is provided
A. to prevent leakage of current
B. to prevent shock
C. both of above factors
D. none of above factors
Answer: C

50. The thickness of insulation provided on the conductor depends on
A. the magnitude of voltage on the conductor
B. the magnitude of current flowing through it
C. both A. and B.
D. none of the above
Answer: A

51. Which of the following quantities remain the same in all parts of a series circuit ?
A. Voltage
B. Current
C. Power
D. Resistance
Answer: B

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

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

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

55. Resistance of a tungsten lamp as applied voltage increases
A. decreases
B. increases
C. remains same
D. none of the above
Answer: B

56. Electric current passing through the circuit produces
A. magnetic effect
B. luminous effect
C. thermal effect
D. chemical effect
(e) all above effects
Answer: C

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

58. If the efficiency of a machine is to be high, what should be low ?
A. Input power
B. Losses
C. True component of power
D. kWh consumed
(e) Ratio of output to input
Answer: B

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

60. Two bulbs of 500 W and 200 W rated at 250 V will have resistance ratio as
A. 4 : 25
B. 25 : 4
C. 2 : 5
D. 5 : 2
Answer: C

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

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

63. It becomes more difficult to remove
A. any electron from the orbit
B. first electron from the orbit
C. second electron from the orbit
D. third electron from the orbit
Answer: D

64. When one leg of parallel circuit is opened out the total current will
A. reduce
B. increase
C. decrease
D. become zero
Answer: C

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

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

67. Resistance of 220 V, 100 W lamp will be
A. 4.84 Q
B. 48.4 Q
C. 484 ft
D. 4840 Q
Answer: C

68. In the case of direct current
A. magnitude and direction of current remains constant
B. magnitude and direction of current changes with time
C. magnitude of current changes with time
D. magnitude of current remains constant
Answer: A

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

70. Resistance of carbon filament lamp as the applied voltage increases.
A. increases
B. decreases
C. remains same
D. none of the above
Answer: B

71. Bulbs in street lighting are all connected in
A. parallel
B. series
C. series-parallel
D. end-to-end
Answer: A

72. For testing appliances, the wattage of test lamp should be
A. very low
B. low
C. high
D. any value
Answer: C

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

74. Sparking occurs when a load is switched off because the circuit has high
A. resistance
B. inductance
C. capacitance
D. impedance
Answer: B

75. Copper wire of certain length and resistance is drawn out to three times its length without change in volume, the new resistance of wire becomes
A. 1/9 times
B. 3 times
(e) 9 times
D. unchanged
Answer: C

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

77. A field of force can exist only between
A. two molecules
B. two ions
C. two atoms
D. two metal particles
Answer: B

78. A substance whose molecules consist of dissimilar atoms is called
A. semi-conductor
B. super-conducto
C. compound
D. insulator
Answer: C

79. International ohm is defined in terms of the resistance of
A. a column of mercury
B. a cube of carbon
C. a cube of copper
D. the unit length of wire
Answer: A

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

91. Which method can be used for absolute measurement of resistances ?
A. Lorentz method
B. Releigh method
C. Ohm’s law method
D. Wheatstone bridge method
Answer: D

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

93. Ohm’s law is not applicable to
A. semi-conductors
B. D.C. circuits
C. small resistors
D. high currents
Answer: A

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

95. A nichrome wire used as a heater coil has the resistance of 2 £2/m. For a heater of 1 kW at 200 V, the length of wire required will be
A. 80 m
B. 60 m
C. 40 m
D. 20 m
Answer: A

96. Temperature co-efficient of resistance is expressed in terms of
A. ohms/°C
B. mhos/ohm°C
(e) ohms/ohm°C
D. mhos/°C
Answer: C

97. Which of the following materials has the least resistivity ?
A. Zinc
B. Lead
C. Mercury
D. Copper
Ans:

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

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

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

101. A rheostat differs from potentiometer in the respect that it
A. has lower wattage rating
B. has higher wattage rating
C. has large number of turns
D. offers large number of tapping
Answer: B

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

103. An open resistor, when checked with an ohm-meter reads
A. zero
B. infinite
C. high but within tolerance
D. low but not zero
Answer: B

104. are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.
A. Varistors
B. Thermistor
C. Semi-conductors
D. Variable resistors
Answer: C

105. All good conductors have high
A. conductance
B. resistance
C. reluctance
D. thermal conductivity
Answer: A

106. Voltage dependent resistors are usually made from
A. charcoal
B. silicon carbide
C. nichrome
D. graphite
Answer: C

107. Voltage dependent resistors are used
A. for inductive circuits
B. to supress surges
C. as heating elements
D. as current stabilizers
Answer: B

108. The ratio of mass of proton to that of electron is nearly
A. 1840
B. 1840
C. 30
D. 4
Answer: A

109. The number of electrons in the outer most orbit of carbon atom is
A. 3
B. 4
C. 6
D. 7
Answer: B

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

111. A thermistor has
A. positive temperature coefficient
B. negative temperature coefficient
C. zero temperature coefficient
D. variable temperature coefficient
Answer: C

112. If/, R and t are the current, resistance and time respectively, then according to Joule’s law heat produced will be proportional to
A. I2Rt
B. I2Rf
C. I2R2t
D. I2R2t*
Answer: A

113. Nichrome wire is an alloy of
A. lead and zinc
B. chromium and vanadium
C. nickel and chromium
D. copper and silver
Answer: C

114. When a voltage of one volt is applied, a circuit allows one micro ampere current to flow through it. The conductance of the circuit is
A. 1 n-mho
B. 106 mho
C. 1 milli-mho
D. none of the above
Answer: A

115. Which of the following can have negative temperature coefficient ?
A. Compounds of silver
B. Liquid metals
C. Metallic alloys
D. Electrolytes
Answer: D

116. Conductance : mho ::
A. resistance : ohm
B. capacitance : henry
C. inductance : farad
D. lumen : steradian
Answer: A

117. 1 angstrom is equal to
A. 10-8 mm
B. 10″6 cm
C. 10″10 m
D. 10~14 m
Answer: C

118. One newton meter is same as
A. one watt
B. one joule
C. five joules
D. one joule second
Answer: B

MAGNETISM and ELECTROMAGNETISM Multiple Choice Questions

1. Tesla is a unit of
(a) field strength
(b) inductance
(c) flux density
(d) flux
Answer: c

2. 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
Answer: d

3. The materials having low retentivity are suitable for making
(a) weak magnets
(b) temporary magnets
(c) permanent magnets
(d) none of the above
Answer: b

4. A magnetic field exists around
(a) iron
(b) copper
(c) aluminium
(d) moving charges
Answer: d

5. Ferrites are materials.
(a) paramagnetic
(b) diamagnetic
(c) ferromagnetic
(d) none of the above
Answer: c

6. Air gap has_______eluctance as compared to iron or steel path
(a) little
(b) lower
(c) higher
(d) zero
Answer: b

7. 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
Answer: b

8. Which of the following is a vector quantity ?
(a) Relative permeability
(b) Magnetic field intensity
(c) Flux density
(d) Magnetic potential
Answer: b

9. 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
Answer: b

10. 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
Answer: b

11. 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
Answer: b

12. 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
Answer: c

13. 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
Answer: b

14. Magnetising steel is normals difficult because
(a) it corrodes easily
(6) it has high permeability
(c) it has high specific gravity
(d) it has low permeability
Answer: d

15. 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
Answer: d

16. The unit of relative permeability is
(a) henry/metre
(b) henry
(c) henry/sq. m
(d) it is dimensionless
Answer: d

17. 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
Answer: a

18. 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
Answer: d

19. 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
Answer: b

20. Indicate which of the following material does not retain magnetism permanently.
(a) Soft iron
(b) Stainless steel
(e) Hardened steel
(d) None of the above
Answer: a

21. The main constituent of permalloy is
(a) cobalt
(b) chromium
(c) nickel
(d) tungsten
Answer: c

22. The use of permanent magnets is. not made in
(a) magnetoes
(6) energy meters
(c) transformers
(d) loud-speakers
Answer: c

23. 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
Answer: c

24. Degaussing is the process of
(a) removal of magnetic impurities
(b) removing gases from the materials
(c) remagnetising metallic parts
(d) demagnetising metallic parts
Answer:

25. Substances which have permeability less than the permeability of free space are known as
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) bipolar
Answer: c

26. Two infinitely long parallel conductors in vacuum any separated 1 metre 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)
Answer: d

27. In the left hand rule, forefinger always represents
(a) voltage
(b) current
(c) magnetic field
(d) direction of force on the conductor
Answer: c

28. Which of the following is a ferromagnetic material ?
(a) Tungsten
(b) Aluminium
(c) Copper
(d) Nickel
Answer: d

29. Ferrites are a sub-group of
(a) non-magnetic materials
(6) ferro-magnetic materials
(c) paramagnetic materials
(d) ferri-magnetic materials
Answer: d

30. Gilbert is a unit of
(a) electromotive force
(6) magnetomotive force
(c) conductance
(d) permittivity
Answer: b

31. 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
Answer: b

32. Reciprocal of permeability is
(a) reluctivity
(b) susceptibility
(c) permittivity
(d) conductance
Answer: a

33. The relative permeability is less than unity is case of
(a) ferromagnetic materials
(b) ferrites
(c) non-ferrous materials
(d) diamagnetic materials
Answer: d

34. Which of the following is the unit of magnetic flux density ?
(a) weber
(b) lumens
(c) tesla
(d) none of the above
Answer: c

35. The magnetism left in the iron after exciting field has been removed is known as
(a) permeance
(b) residual magnetism
(c) susceptance
(d) reluctance
Answer: b

36. Which of the following is not a unit of flux?
(a) Maxwell
(b) Telsa
(c) Weber
(d) All of the above
Answer: b

37. Which of the following is expected to have the maximum permeability ?
(a) Brass
(b) Copper
(c) Zinc
(d) Ebonite
Answer: d

38. One telsa is equal to
(a) 1 Wb/mm2
(b) 1 Wb/m
(c) 1 Wb/m2
(d) 1 mWb/m2
Answer: c

39. 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
Answer: b

40. 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
Answer: a

41. One maxwell is equal to
(a) 10 webers
(b) 10 webers
(c) 10 webers
(d) 10 webers
Answer: d

42. 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
Answer: d

43. Susceptibility is positive for
(a) non-magnetic substances
(b) diamagnetic substances
(c) ferromagnetic substances
(d) none of the above
Answer: c

44. 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
Answer: d

45. 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
Answer: c

46. 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]
Answer: c

47. 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
Answer: b

48. What is the magnitude and the direction of force per 1.1m length of a pair of conductors of a direct current linecarrying 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
Answer: d

49. 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
Answer: c

50. The unit of flux is the same as that of
(a) reluctance
(b) resistance
(c) permeance
(d) pole strength
Answer: d

51. Unit for quantity of electricity is
(a) ampere-hour
(b) watt
(c) joule
(d) coulomb
Answer: d

52. 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
Answer: c

53. 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
Answer: a

54. The commonly used material for shielding or screening magnetism is
(a) copper
(b) aluminium
(c) soft iron
(d) brass
Answer: c

55. 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
Answer: d

56. 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
Answer: a

57. The retentivity (a property) of material is useful for the construction of
(a) permanent magnets
(b) transformers
(c) non-magnetic substances
(d) electromagnets
Answer: a

58. The relative permeability of materials is not constant.
(a) diamagnetic
(b) paramagnetic
(c) ferromagnetic
(d) insulating
Answer: c

59. The materials are a bit inferior conductors of magnetic flux than air.
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) dielectric
Answer: c

60. 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
Answer: c

61. 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
Answer: b

62. 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
Answer: d

63. Magnetic moment is a
(a) pole strength
(6) universal constant
(c) scalar quantity
(d) vector quantity
Answer: d

64. 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
Answer: c

65. 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
Answer: c

66. 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
Answer: c

67. 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
Answer: b

68. 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
Answer: b

69. Which of the following statements is correct ?
(a) The magnetic flux inside an exciting coil is lower than its outside surface
(6) The magnetic flux inside an exciting coil is zero
(e) 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
Answer: d

70. A certain amount of current flows through a ring-shaped coil with fixed number of turns. How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional change of coil ?
(a) Decreases
(b) Increases
(c) Remains same
(d) First increases and then decreases depending on the depth of iron in¬sertion
Answer: b

71. The magnetic reluctance of a material
(a) decreases with increasing cross sectional area of material
(6) increases with increasing cross-sec-tional area of material
(c) does not vary with increasing cross-sectional area of material
(d) any of the above
Answer: a

72. 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
Answer: d

73. 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
Answer: c

74. 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
Answer: d

75. 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
Answer: d

76. The bar magnet has
(a) the dipole moment
(b) monopole moment
(c) (a) and (b) both
(d) none of the above
Answer: a

77. Which of the following materials are diamagnetic ?
(a) Silver
(b) Copper
(c) Silver and copper
(d) Iron
Answer: c

78. 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
Answer: c

79. 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
Answer: a

91. For which of the following materials the saturation value is the highest ?
(a) Ferromagnetic materials
(6) Paramagnetic materials
(c) Diamagnetic materials
(d) Ferrites
Answer: d

92. 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
Answer: c

93. For which of the following materials the net magnetic moment should be zero ?
(a) Diamagnetic materials
(b) Ferrimagnetic materials
(c) Antiferromagnetic materials
(d) Antiferrimagnetic materials
Answer: c

94. 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
Answer: d

95. 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
Answer: a

96. Temporary magnets are used in
(a) loud-speakers
(b) generators
(c) motors
(d) all of the above
Answer: d

97. 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
Answer: c

98. 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
Answer:

99. Core of an electromagnet should have
(a) low coercivity
(6) high susceptibility
(c) both of the above
(d) none of the above
Answer: c

100. Magnetism of a magnet can be destroyed by
(a) heating
(b) hammering
(c) by inductive action of another magnet
(d) by all above methods
Answer: d

MAGNETISM and ELECTROMAGNETISM Multiple Choice Questions and Answers ::

MAGNETIC CIRCUIT Multiple Choice Questions with Answers :-

1. An air gap is usually inserted in magnetic circuits to
A. increase m.m.f.
B. increase the flux
C. prevent saturation
D. none of the above
Answer: C

2. The relative permeability of a ferromagnetic material is
A. less than one
B. more than one
C. more than 10
D. more than 100 or 1000
Answer: D

3. The unit of magnetic flux is
A. henry
B. weber
C. ampereturn/weber
D. ampere/metre
Answer: B

4. Permeability in a magnetic circuit corresponds to______ in an electric circuit.
A. resistance
B. resistivity
C. conductivity
D. conductance
Answer: C

5. 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
Answer: A

6. Relative permeability of vacuum is
A. 1
B. 1 H/m
C. 1/4JI
D. 4n x 10-‘ H/m
Answer: A

7. Permanent magnets are normally made of
A. alnico alloys
B. aluminium
C. cast iron
D. wrought iron
Answer: A

8. Energy stored by a coil is doubled when its current is increased by percent.
A. 25
B. 50
C.41.4
D. 100
Answer: C

9. Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hystersis loss.
A. high, high
B. low, high
C. high, low
D. low, low
Answer: C

10. 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
Answer: B

11. 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
Answer: A

12. 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
Answer: B

13. A material for good magnetic memory should have
A. low hysteresis loss
B. high permeability
C. low retentivity
D. high retentivity
Answer: D

14. Conductivity is analogous to
A. retentivity
B. resistivity
C. permeability
D. inductance
Answer: C

15. In a magnetic material hysteresis loss takes place primarily due to
A. rapid reversals of its magnetisation
B. flux density lagging behind magnetising force
C. molecular friction
D. it high retentivity
Answer: D

16. Those materials are well suited for making permanent magnets which have _____ retentivity and _______ coercivity.
A. low, high
B. high, high
C. high, low
D. low, low
Answer: B

17. If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be
A. zero
B. small
C. large
D. none of the above
Answer: C

18. Hard steel is suitable for making permanent magnets because
A. it has good residual magnetism
B. its hysteresis loop has large area
C. its mechanical strength is high
D. its mechanical strength is low
Answer: A

19. Silicon steel is used in electrical machines because it has
A. low coercivity
B. low retentivity
C. low hysteresis loss
D. high coercivity
Answer: C

20. Conductance is analogous to
A. permeance
B. reluctance
C. flux
D. inductance
Answer: A

21. The property of a material which opposes the creation of magnetic flux in it is known as
A. reluctivity
B. magnetomotive force
C. permeance
D. reluctance
Answer: D

22. The unit of retentivity is
A. weber
B. weber/sq. m
C. ampere turn/meter
D. ampere turn
Answer: B

23. Reciprocal of reluctance is
A. reluctivity
B. permeance
C. permeability
D. susceptibility
Answer: B

24. While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit ?
A. E.m.f.
B. Current
C. Current density
D. Conductivity
Answer: B

25. The unit of reluctance is
A. metre/henry
B. henry/metre
C. henry
D. 1/henry
Answer: D

26. A ferrite core has less eddy current loss than an iron core because
A. ferrites have high resistance
B. ferrites are magnetic
C. ferrites have low permeability
D. ferrites have high hysteresis
Answer: A

27. Hysteresis loss least depends on
A. volume of material
B. frequency
C. steinmetz coefficient of material
D. ambient temperature
Answer: D

28. Laminated cores, in electrical machines, are used to reduce
A. copper loss
B. eddy current loss
C. hysteresis loss
D. all of the above
Answer: B

MAGNETIC CIRCUIT objective questions with answers pdf download online exam test

Electromagnetic Induction Multiple Choice Questions :-

1. The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as
(a) self-inductance
(b) mutual inductance
(c) series aiding inductance
(d) capacitance
Answer: a

2. As per Faraday’s laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it
(a) lies perpendicular to the magnetic flux
(b) lies in a magnetic field
(e) cuts magnetic flux
(d) moves parallel to the direction of the magnetic field
Answer: c

3. Which of the following circuit element stores energy in the electromagnetic field ?
(a) Inductance
(b) Condenser
(c) Variable resistor
(d) Resistance
Answer: a

4. The inductance of a coil will increase under all the following conditions except
(a) when more length for the same number of turns is provided
(6) when the number of turns of the coil increase
(c) when more area for each turn is provided
(d) when permeability of the core increases
Answer: a

5. Higher the self-inductance of a coil,
(a) lesser its weber-turns
(b) lower the e.m.f. induced
(c) greater the flux produced by it
(d) longer the delay in establishing steady current through it
Answer: d

6. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will
(a) increase
(b) decrease
(c) remain the same
(d) initially increase and then decrease
Answer: b

7. An open coil has
(a) zero resistance and inductance
(b) infinite resistance and zero inductance
(c) infinite resistance and normal inductance
(d) zero resistance and high inductance
Answer: b

8. Both the number of turns and the core length of an inductive coil are doubled.
Its self-inductance will be
(a) unaffected
(b) doubled
(c) halved
(d) quadrupled
Answer: b

9. If current in a conductor increases then according to Lenz’s law self-induced voltage will
(a) aid the increasing current
(b) tend to decrease the amount of cur-rent
(c) produce current opposite to the in-creasing current
(d) aid the applied voltage
Answer: c

10. The direction of induced e.m.f. can be found by
(a) Laplace’s law
(b) Lenz’s law
(c) Fleming’s right hand rule
(d) Kirchhoff s voltage law
Answer: b

11. Air-core coils are practically free from
(a) hysteresis losses
(b) eddy current losses
(c) both (a) and (b)
(d) none of the above
Answer: c

12. The magnitude of the induced e.m.f. in a conductor depends on the
(a) flux density of the magnetic field
(b) amount of flux cut
(c) amount of flux linkages
(d) rate of change of flux-linkages
Answer: d

13. Mutually inductance between two magnetically-coupled coils depends on
(a) permeability of the core
(b) the number of their turns
(c) cross-sectional area of their common core
(d) all of the above
Answer: d

14. A laminated iron core has reduced eddy-current losses because
(a) more wire can be used with less D.C. resistance in coil
(b) the laminations are insulated from each other
(c) the magnetic flux is concentrated in the air gap of the core
(d) the laminations are stacked vertfcally
Answer: b

15. The law that the induced e.m.f. and current always oppose the cause producing them is due to
(a) Faraday
(b) Lenz
(c) Newton
(d) Coulomb
Answer: b

16. Which of the following is not a unit of inductance ?
(a) Henry
(b) Coulomb/volt ampere
(c) Volt second per ampere
(d) All of the above
Answer: b

17. In case of an inductance, current is proportional to
(a) voltage across the inductance
(b) magnetic field
(c) both (a) and (b)
(d) neither (a) nor (b)
Answer: b

18. Which of the following circuit elements will oppose the change in circuit current ?
(a) Capacitance
(b) Inductance
(c) Resistance
(d) All of the above
Answer: b

19. For a purely inductive circuit which of the following is true ?
(a) Apparent power is zero
(b) Relative power is.zero
(c) Actual power of the circuit is zero
(d) Any capacitance even if present in the circuit will not be charged
Answer: c

20. Which of the following is unit of inductance ?
(a) Ohm
(b) Henry
(c) Ampere turns
(d) Webers/metre
Answer: b

21. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be
(a) 64 A/s
(b) 32 A/s
(c) 16 A/s
(d) 4 A/s
Answer: d

22. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core length is doubled, all other quantities, remaining the same, the inductance will be
(a) 3 mH
(b) 12 mH
(c) 24mH
(d)48mH
Answer: a

23. The self inductances of two coils are 8 mH and 18 mH. If the co-efficients of coupling is 0.5, the mutual inductance of the coils is
(a) 4 mH
(b) 5 mH
(c) 6 mH
(d) 12 mH
Answer: c

24. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be
(a) 32 mH
(b) 38 mH
(c) 40 mH
(d) 48 mH
Answer: b

25. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400 turns, all other quantities (area, length etc.) remaining the same, the inductance will be
(a) 6 mH
(b) 14 mH
(c) 24 mH
(d) 48 mH
Answer: d

26. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If the two coils are connected in series, the total inductance will be
(a) 6 H
(b) 8 H
(c) 12 H
(d) 24 H
Answer: c

27. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling will be
(a) 2.0
(b) 1.0
(c) 0.5
(d) zero
Answer: b

28. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is
(a) 50 ohms
(b) 500 ohms
(c) 1000 ohms
(d) 5000 ohms
Answer: d

29. A conductor 2 meters long moves at right angles to a magnetic field of flux density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
(a) 10 V
(6) 15 V
(c) 25V
(d) 50V
Answer: c

30. Lenz’s law is a consequence of the law of conservation of
(a) induced current
(b) charge
(c) energy
(d) induced e.m.f.
Answer: c

31. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly
(a) 50 N
(b) 120 N
(c) 240 N
(d) 480 N
Answer: b

32. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right angles to a magnetic field having a flux density of 0.67 tesla.
(a) 100 N
(b) 400 N
(c) 600 N
(d) 1000 N
Answer: a

33. The co-efficient of coupling between two air core coils depends on
(a) self-inductance of two coils only
(b) mutual inductance between two coils only
(c) mutual inductance and self inductance of two coils
(d) none of the above
Answer: c

34. An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in flux which occurs in 0.5 second. The total flux change is
(a) 20 Wb
(b) 2 Wb
(c) 0.2 Wb
(d) 0.02 Wb
Answer: d

35. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage ?
(a) 0.01 s
(b) 0.1 s
(c) 0.5 s
(d) 5 s
Answer: c

36. Which of the fpllowing inductor will have the least eddy current losses ?
(a) Air core
(b) Laminated iron core
(c) Iron core
(d) Powdered iron core
Answer: a

37. A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of inductance is
(a) 3500 mH
(b) 350 mH
(c) 250 mH
(d) 150 mH
Answer: b

38. Two 300 uH coils in series without mutual coupling have a total inductance of
(a) 300 uH
(b) 600 uH
(c) 150 uH
(d) 75 uH
Answer: b

39. Current changing from 8 A to 12 A in one second induced 20 volts in a coil. The value of inductance is
(a) 5 mH
(b) 10 mH
(c) 5 H
(d) 10 H
Answer: c

40. Which circuit element(s) will oppose the change in circuit current ?
(a) Resistance only
(b) Inductance only
(c) Capacitance only
(d) Inductance and capacitance
Answer: b

41. A crack in the magnetic path of an inductor will result in
(a) unchanged inductance
(b) increased inductance
(c) zero inductance
(d) reduced inductance
Answer: d

42. A coil is wound on iron core which carries current I. The self-induced voltage in the coil is not affected by
(a) variation in coil current
(b) variation in voltage to the coil
(c) change of number of turns of coil
(d) the resistance of magnetic path
Answer: b

43. A moving magnetic field will produce the same effect as a conductor that is moving.
(a) Yes
(b) No
Ans:

44. The polarity of the induced voltage can be determined by using the left-hand generator rule.
(a) Yes
(b) No
Answer: a

45. Increasing the field or increasing the current will decrease the force on the conductor.
(a) Yes
(b) No
Answer: b

46. Reversing the field or the current will reverse the force on the conductor.
(a) Yes
(b) No
Answer: a

49. When a conductor moves in the field, so that it makes an angle 8 with the lines of flux, the force F is given as : F = Bl sin2 0.
(a) Yes
(b) No
Answer: b

50. The self-inductance of the coil may be defined as equal to the e.m.f. induced in volts when the current in the circuit changes at the rate of unit Weber turns.
(a) Yes
(b) No
Answer: b

SINGLE PHASE INDUCTION MOTORS Multiple Choice Questions :-

1. 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 inductiance

Answer: B

2. 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.

Answer: A

3. 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

Answer: A

4. 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

Answer: A

5. In a capacitor start motor, the phase displacement between starting and running winding can be nearly

A. 10°
B. 30°
C. 60°
D. 90°

Answer: D

6. 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

Answer: A

7. The rotor developed by a single-phase motor at starting is

A. more than i.he rated torque
B. rated torque
C. less than the rated torque
D. zero

Answer: D

8. 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

Answer: A

9. 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

Answer: A

10. 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

Answer: B

11. 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

Answer: D

12. 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

Answer: C

13. 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

Answer: A

14. 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

Answer: C

15. 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

Answer: B

16. 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

Answer: A

17. 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

Answer: D

18. 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

Answer: D

19. Which of the following motors is used in mixies ?

A. Repulsion motor
B. Reluctance motor
C. Hysteresis motor
D. Universal motor

Answer: D

20. Which of the following motors is inherently self starting ?

A. Split motor
B. Shaded-pole motor
C. Reluctance motor
D. None of these

Answer: B

21. 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

Answer: B

22. Burning out of winding is due to

A. short circuited capacitor
B. capacitor value hiving changed
C. open circuiting of capacitor
D. none of the above

Answer: A

23. 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)

Answer: C

24. Short-circuiter is used in

A. repulsion induction motor
B. repulsion motor
C. repulsion start induction run motor
D. none of the above

Answer: C

25. 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%

Answer: D

26. 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

Answer: D

27. The power factor of a single-phase induction motor is usually

A. lagging
B. always leading
C. unity
D. unity to 0.8 leading

Answer: A

28. A shaded pole motor can be used for

A. toys
B. hair dryers
C. circulators
D. any of the above

Answer: D

29. A hysteresis motor works on the principle of

A. hysteresis loss
B. magnetisation of rotor
C. eddy current loss
D. electromagnetic induction

Answer: A

30. 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

Answer: B

31. For which of the applications a reluctance motor is preferred ?

A. Electric shavers
B. Refrigerators
C. Signalling and timing devices
D. Lifts and hoists

Answer: C

32. 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

Answer: C

33. 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

Answer: B

34. 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

Answer: C

35. A schrage motor can run on

A. zero slip
B. negative slip
C. positive slip
D. all of the above

Answer: D

36. 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

Answer: C

37. 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

Answer: A

38. 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

Answer: A

39. In split-phase motor auxiliary winding is of

A. thick wire placed at the bottom of the slots
B. thick wire placed at the top of the slots
C. thin wire placed at the top of the slots
D. thin wire placed at the bottom of the slots

Answer: C

40. 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

Answer: D

41. 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

Answer: B

42. 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

Answer: A

43. 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

Answer: C

44. 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

Answer: C

45. Which of the following motors has highest starting torque ?

A. Repulsion motor
B. Shaped pole motor
C. Capacitor-start motor
D. Split-phase motor

Answer: C

46. The repulsion-start induction-run motor is used because of

A. good power factor
B. high efficiency
C. minimum cost
D. high starting torque

Answer: D

47. 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

Answer: A

48. 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

Answer: D

49. 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

Answer: C

50. 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

Answer: A

51. 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

Answer: C

52. 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

Answer: D

53. The speed of a universal motor is generally reduced by using

A. gear trains
B. V-belts
C. brakes
D. chains

Answer: A

54. 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

Answer: D

55. 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

Answer: A

56. 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

Answer: C

57. 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

Answer: C

58. Which motor is normally free from mechanical and magnetic vibrations ?

A. Split phase motor
B. Universal motor
C. Hysteresis motor
D. Shaded pole motor

Answer: C

59. 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

Answer: C

60. A reluctance motor

A. is self-starting
B. is constant speed motor
C. needs no D.C. excitation
D. all of the above

Answer: D

61. In a hysteresis motor, the rotor must have

A. retentivity
B. resistivity
C. susceptibility
D. none of the above

Answer: A

62. The rotor of a hysteresis motor is made of

A. aluminium
B. cast iron
C. chrome steel
D. copper

Answer: C

63. The electric motor used in portable drills is

A. capacitor run motor
B. hysteresis motor
C. universal motor
D. repulsion motor

Answer: C

64. 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

Answer: C

65. 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

Answer: B

66. Torque developed by a single phase induction motor at starting is

A. pulsating
B. uniform
C. none of the above
D. nil

Answer: D

67. 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

Answer: C

68. 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

Answer: A

69. 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

Answer: A

70. 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

Answer: C

71. In a ceilingfan 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

Answer: A

72. The shaded pole motor is used for

A. high starting torque
B. low starting torque
C. medium starting torque
D. very high starting torque

Answer: B

73. 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

Answer: C

74. 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

Answer: C

75. 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

Answer: B

76. Which of the following motors is used for unity power factor ?

A. Hysteresis motor
B. Schrage motor
C. Universal motor
D. Reluctance motor

Answer: B

77. 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

Answer: C

78. 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

Answer: B

79. 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)

Answer: D

80. 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

Answer: B

81. 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

Answer: A

82. 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

Answer: A

83. Which of the following motors is used in tape-recorders ?

A. Hysteresis motor
B. Reluctance motor
C. Capacitor-run motor
D. Universal motor

Answer: A

84. 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

Answer: B

85. 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

Answer: C

86. 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

Answer: D

87. 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

88. 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

Answer: C

89. 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

Answer: D

90. 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

Answer: A

91. To reverse the direction of rotation of acapacitor 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

Answer: A

92. 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

Answer: D

93. 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

Answer: B

94. A shaded pole motor does not possess

A. centrifugal switch
B. capacitor
C. commutator
D. all of the above

Answer: D

95. In a A.C. series motor armature coils are usually connected to commutator

A. through resistance
B. through reactances
C. through capacitors
D. solidly

Answer: A

96. 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 unsym-metrical magnetic construction in order to vary reluctance path between stator and rotor

Answer: A

97. 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

Answer: A

98. A repulsion motor is equipped with

A. slip rings
B. commutator
C. both
A. and (b)
D. none of the above

Answer: B

99. The capacitors used in single-phase capacitor motors have no

A. voltage rating
B. dielectric medium
C. polarity marking
D. definite value

Answer: C

100. 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

Answer: D

101. After the starting winding of a single phase induction motor is disconnected from supply, it continues to run only on

A. running winding
B. rotor winding
C. field winding
D. compensating winding

Answer: A

102. Which of the following statements regarding repulsion-start induction motor is incorrect ?

A. It requires more maintenance of commutator and other mechanical devices
B. It makes quite a bit of noise on starting
C. In fractional horse power motors, it has replaced the capacitor motors
D. It is not easily reversed

Answer: C

103. A.C. series motor as compared to D.C. series motor has

A. smaller brush width
B. less number of field turns
C. more number of armature turns
D. less air gap
(e) all of the above
Ans: e

104. Locked rotor current of a shaded pole motor is

A. equal to full load current
B. less than full load current
C. slightly more than full load current
D. several times the full load current

Answer: C

105. Speed control of a universal motor is achieved by

A. varying field flux with tapped field windings
B. connecting rheostat in series
C. applying variable voltage by means of silicon controlled rectifier
D. applying variable voltage by means of variable auto-transformer
(e) all of the above methods
Ans: e

116. Hysteresis motor is particularly useful for high-quality record players and tape-recorders because

A. it revolves synchronously
B. it is not subject to any magnetic or mechanical vibrations
C. it can be easily manufactured in extremely small sizes of up to 1 W output
D. it develops hysteresis torque which is extremely steady both in amplitude and phase

Answer: D

117. Which of the following statements regarding hysteresis motor is in incorrect ?

A. It is extremely sensitive to fluctuations in supply voltage
B. Its high starting torque is due to its high rotor hysteresis loss
C. It is extremely quiet in operation
D. It accelerates from rest to full-speed almost instantaneously

Answer: A

118. Which of the following statements regarding single-phase induction motoris correct ?

A. It requires only one winding
B. It can rotate in one direction only
C. It is self-starting
D. It is not self-starting

Answer: D

119. The starting winding of a single-phase motor is placed in

A. armature
B. field
C. rotor
D. stator

Answer: D

120. The speed of a universal motor is usually reduced by using

A. gearing
B. belts
C. brakes
D. chains

Answer: A

Synchronous Motors Questions :-

1. Synchronous motors are generally not self-starting because
A. the direction of rotation is not fixed
B. the direction of instantaneous torque reverses after half cycle
C. startes cannot be used on these machines
D. starting winding is not provided on the machines
Answer: B

2. In case one phase of a three-phase synchronous motor is short-circuited the motor will
A. not start
B. run at 2/3 of synchronous speed
C. run with excessive vibrations
D. take less than the rated load
Answer: A

3. A pony motor is basically a
A. small induction motor
B. D.C. series motor
C. D.C. shunt motor
D. double winding A.C./D.C. motor
Answer: A

4. A synchronous motor can develop synchronous torque
A. when under loaded
B. while over-excited
C. only at synchronous speed
D. below or above synchronous speed
Answer: C

5. A synchronous motor can be started by
A. pony motor
B. D.C. compound motor
C. providing damper winding
D. any of the above
Answer: D

6. A three-phase synchronous motor will have
A. no slip-rings
B. one slip-ring
C. two slip-rings
D. three slip-rings
Answer: C

7. Under which of the following conditions hunting of synchronous motor is likely to occur ?
A. Periodic variation of load
B. Over-excitation
C. Over-loading for long periods
D. Small and constant load
Answer: A

8. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
A. the motor stops
B. it runs as a reluctance motor at the same speed
C. it runs as a reluctance motor at a lower speed
D. none of the above
Answer: A

9. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
A. V
B. V312
C. V2
D. 1/V
Answer: A

10. The power developed by a synchronous motor will be maximum when the load angle is
A. zero
B. 45°
C. 90°
D. 120°
Answer: C

11. A synchronous motor can be used as a synchronous capacitor when it is
A. under-loaded
B. over-loaded
C. under-excited
D. over-excited
Answer: D

12. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
A. power factor as well as armature current will decrease
B. power factor as well as armature current will increase
C. power factor will increase but armature current will decrease
D. power factor will decrease and armature current will increase
Answer: D

13. Mostly, synchronous motors are of
A. alternator type machines
(6) induction type machines
C. salient pole type machines
D. smooth cylindrical type machines
Answer: C

14. The synchronous motor is not inherently self-starting because
A. the force required to accelerate the rotor to the synchronous speed in an instant is absent
B. the starting device to accelerate the rotor to near synchronous speed is absent
C. a rotating magnetic field does not have enough poles
D. the rotating magnetic field is produced by only 50 Hz frequency currents
Answer: A

15. As the load is applied to a synchronous motor, the motor takes more armature current because
A. the increased load has to take more current
B. the rotor by shifting its phase backward causes motor to take more current
C. the back e.m.f. decreases causing an increase in motor current
D. the rotor strengthens the rotating field casuing more motor current
Answer: B

16. Synchronous motor always runs at
A. the synchronous speed
B. less than synchronous speed
C. more than synchronous speed
D. none of the above
Answer: A

17. An over-excited synchronous motor takes
A. leading current
B. lagging current
C. both A. and B.
D. none of the above
Answer: A

18. The working of a synchronous motor is similar to
A. gear train arrangement
B. transmission of mechancial power by shaft
C. distribution transformer
D. turbine
E. none of the above
Answer: B

19. The minimum armature current of the synchronous motor corresponds to operation at
A. zero power factor leading
B. unity power factor
C. 0.707 power factor lagging
D. 0.707 power factor leading
Answer: B

20. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on
A. d.c. excitation only
B. speed of the motor
C. load on the motor
D. both the speed and rotor flux
Answer: A

21. If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is
A. 2
B. 3
C. 4
D. 6
Answer: B

22. For V-curves for a synchronous motor the graph is drawn between
A. field current and armature current
B. terminal voltage and load factor
C. power factor and field current
D. armature current and power factor
Answer: A

23. The back e.m.f. of a synchronous motor depends on
A. speed
B. load
C. load angle
D. all of the above
Answer: C

24. A synchronous motor can operate at
A. lagging power factor only
(6) leading power factor only
C. unity power factor only
D. lagging, leading and unity power factors
Answer: D

25. In a synchronous motor which loss varies with load ?
A. Windage loss
B. Bearing friction loss
C. Copper loss
D. Core loss
Answer: C

26. A synchronous motor can be made self starting by providing
A. damper winding on rotor poles
B. damper winding on stator
C. damper winding on stator as well as rotor poles
D. none of the above
Answer: A

27. The oscillations in a synchronous motor can be damped out by
A. maintaining constant excitation
B. running the motor on leading power factors
C. providing damper bars in the rotor pole faces
D. oscillations cannot be damped
Answer: C

28. The shaft of synchronous motor is made of
A. mild steel
B. chrome steel
C. alnico
D. stainless steel
Answer: A

29. When the field of a synchronous motor is under-excited, the power factor will be
A. leading
B. lagging
C. unity
D. zero
Answer: B

30. The speed regulation of a synchronous motor is always
A. 1%
B. 0.5%
C. positive
D. zero
Answer: D

31. The percentage slip in case of a synchronous motor is
A. 1%
B. 100%
C. 0.5%
D. zero
Answer: D

32. The operating speed of a synchronous motor can be changed to new fixed value by
A. changing the load
B. changing the supply voltage
C. changing frequency
D. using brakes
Answer: C

33. A synchronous motor will always stop when
A. supply voltage fluctuates
B. load in motor varies
C. excitation winding gets disconnected
D. supply voltage frequency changes9885859805
Answer: C

34. riunting in a synchronous motor takes place
A. when supply voltage fluctuates
B. when load varies
C. when power factor is unity
D. motor is under loaded
Answer: B

35. When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is
A. more
B. less
C. equal
D. twice
Answer: B

36. The rotor copper losses, in a synchronous motor, are met by
A. d.c. source
B. armature input
C. motor input
D. supply lines
Answer: A

37. The maximum power developed in a synchronous motor occurs at a coupling angle of
A. 30°
B. 60°
C. 90°
D. 180°
Answer: C

38. When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor
A. remains same as the original value
B. decreases to half the original value
C. tends to becomes zero
D. increases to two times the original value
Answer: D

39. In which of the following motors the stator and rotor magnetic field rotate at the same speed ?
A. Universal motor
B. Synchronous motor
C. Induction motor
D. Reluctance motor
Answer: B

40. Synchronsizingpower of a synchronous machine is
A. direcly proportional to the synchronous reactance
(6) inversely proportional to the synchronous reactance
A. equal to the synchronous reactance
D. none of the above
Answer: B

41. Synchronous motors are
A. not-self starting
B. self-starting
C. essentially self-starting
D. none of the above
Answer: A

42. The standard full-load power factor ratings for synchronous motors are
A. zero or 0.8 leading
B. unity or 0.8 lagging
C. unity or 0.8 leading
D. unity or zero
Answer: C

43. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in
A. back e.m.f.
B. armature current
C. power factor
D. torque angle
Answer: B

44. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
A. synchronous motor has no slip
B. stator supply is not required to produce magnetic field
C. mechanical load on the rotor remains constant
D. synchronous motor has large airgap
Answer: B

45. A synchronous motor working at leading power factor can be used as
A. voltage booster
B. phase advancer
C. noise generator
D. mechanical synchronizer
Answer: B

46. Slip rings are usually made of
A. carbon or graphite
B. brass or steel
C. silver or gold
D. copper or aluminium
Answer: B

47. An over excited synchronous motor is used for
A. fluctuating loads
B. variable speed loads
C. low torque loads
D. power factor corrections
Answer: D

48. When the voltage applied to a synchronous motor is increased, which of the following will reduce ?
A. Stator flux
B. Pull in torque
C. Both A. and B.
D. None of the above
Answer: D

51. The efficiency of a properly designed synchronous motor will usually fall in range
A. 60 to 70%
(6) 75 to 80%
C. 85 to 95%
D. 99 to 99.5%
Answer: C

52. To limit the operating temperature an electrical machine should have proper
A. voltage rating
B. current rating
C. power factor
D. speed
Answer: B

53. Slip-rings in a synchronous motor carry
A. direct current
B. alternating current
C. no current
D. all of the above
Answer: A

54. A synchronous machine with large air gap has
A. a higher value of stability limit
(6) a small value of inherent regulation
C. a higher synchronizing power which makes the machine less sensitive to load variations
D. all of the above
Answer: D

55. The armature current of the synchronous motor has higher values for
A. high excitation only
B. low excitation only
C. both A. and B.
D. none of the above
Answer: C

56. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately
A. one-third
B. twice
C. thrice
D. six times
E. nine times
Answer: C

57. The angle between the rotating stator flux and rotor poles is called _____ angle.
A. torque
B. obtuse
C. synchronizing
D. power factor
Answer: A

58. Which of the following methods is used to start a synchronous motor ?
A. Damper winding
B. Star-delta starter
C. Damper winding in conjunction with star-delta starter
D. Resistance starter in the armature circuit
Answer: C

59. When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop
A. inductor motor torque
B. induction generator torque
C. synchronous motor torque
D. d.c. motor toque
E. none of the above
Answer: B

60. An important advantage of a synchronous motor over wound round induction motor is that
A. its power factor may be varied at will
B. its speed is independent of supply frequency
C. its speed may be controlled more easily
D. none of the above
Answer: A

61. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of
A. zero degree
B. two degrees
C. five degrees
D. ten degrees
Answer: C

62. Power factor of a synchronous motor is unity when
A. the armature current is maximum
B. the armature current is minimum
C. the armature current is zero
D. none of the above
Answer: B

63. Change of D.C. excitation of a synchronous motor changes
A. applied voltage of the motor
B. motor speed
C. power factor of power drawn by the motor
D. any of the above
E. all of the above
Answer: C

64. While starting a synchronous motor by induction motor action, field winding is usually
A. connected to D.C. supply
B. short-circuited by low resistance
C. kept open-circuited
D. none of the above
Answer: B

65. Which of the following motors will be used in electric clocks ?
A. D.C. shunt motor
B. D.C. series motor
C. A.C. induction motor
D. A.C. synchronous motor
Answer: D

SYNCHRONOUS MOTORS Multiple Choice Questions and Answers

66. If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor
A. become more
B. become less
C. remain constant
D. none of the above
Answer: B

67. A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will
A. remain same
B. go down
C. improve
D. none of the above
Answer: C

68. While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by
A. induction motor torque in field winding
B. induction motor torque in damper winding
C. eddy current and hysteresis torque in pole faces
D. reHetance motor torque due to saliency of the rotor
E. all of the above methods
Answer: E

69. Armature of a synchronous machine is
A. of reducing number of slip rings on the rotor
B. armature is associated with large power as compared to the field circuits
C. of difficulty of providing high voltage insulation on rotor
D. all of the above reasons
Answer: D

70. If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
A. increase in both armature current and power factor angle
B. increase in back e.m.f. but decrease in armature current
C. increase in both armature current and power factor which is lagging
D. increase in torque angle but decrease in back e.m.f.
Answer: A

71. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
A. augments it directly
B. directly opposes it
C. cross-magnetises it
D. none of the above
Answer: B

72. Stability of a synchronous machine
A. decreases with increase in its excitation
B. increases with increase in its excitation
C. remains unaffected with increase in excitation
D. any of the above
Answer: B

73. The power factor of a synchronous motor is better than that of induction motor because
A. stator supply is relieved of responsibility of producing magnetic field
B. mechanical load on the motor can be adjusted
C. synchronous motor runs at synchronous speed
D. synchronous motor has large air gap
Answer: A

74. If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor
A. will become more
B. will become less
C. will remain unchanged
D. none of the above.
Answer: B

75. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
A. speed of the motor is reduced
B. power factor is decreased
C. Eb (back e.m.f.) becomes less than V (applied voltage)
D. Er (net resultant voltage) in armature is increased
E. none of the above
Answer: D

76. If one-phase of a 3-phase synchronous motor is short-circuited, motor
A. will refuse to start
B. will overheat in spots
C. will not come upto speed
D. will fail to pull into step
Answer: A

77. If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then
A. it runs at a slower speed
B. the motor stops
C. it continues to run at the same speed
D. it runs at a very high speed
Answer: B

78. In which of the following motors the stator and rotor fields rotate simultaneously ?
A. D.C. motor
B. Reluctance motor
C. Universal motor
D. Synchronous motor
E. Induction motor
Answer: D

79. The speed of a synchronous motor
A. increases as the load increases
B. decreases as the load decreases
C. always remains constant
D. none of the above
Answer: C

80. A rotory converter can also be run as a
A. d.c. shunt motor
B. d.c. series motor
C. d.c. compound motor
D. induction motor
E. synchronous motor
Answer: E

81. The maximum speed variation in a 3-phase synchronous motor is
A. 10 per cent
B. 6 per cent
C. 4 per cent
D. 2. per cent
E. zero
Answer: E

82. Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ?
A. Phase to phase winding resistance
B. Stator winding to earthed frame
C. Rotor winding to earthed shaft
D. All of the above
Answer: D

83. Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ?
A. High field current
B. Low short circuit ratio
C. High core losses
D. Low field current
Answer: D

84. In a synchronous motor, the maximum power developed depends on all of the following except
A. rotor excitation
B. maximum value of coupling angle
C. direction of rotation
D. supply voltage
Answer: C

85. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
A. supplied with unbalanced voltage
B. under-loaded
C. over-loaded
D. none of the above
Answer: A

86. In a synchronous motor, damper windings are provided on
A. stator frame
B. rotor shaft
C. pole faces
D. none of the above
Answer: C

87. The induced e.m.f. in a synchronous motor working on leading power factor will be
A. more than the supply voltage
B. less than the supply voltage
C. equal to the supply voltage
Answer: A

88. The effect of increasing the load on a synchronous motor running with normal excitation is to
A. decrease both armature current and power factor
(6) decrease armature current but increase power factor
C. increase armature current but decrease power factor
D. increase both its armature current and power factor
Answer: C

89. The net armature voltage of a synchronous motor is equal to the
A. vector sum of Eb and V
B. arithmetic sum of Eb and V
C. arithmetic difference of Eb and V
D. vector difference of Eh and V
Answer: D

90. The ratio of starting torque to running torque in a synchronous motor is
A. zero
B. one
C. two
D. infinity
Answer: A

91. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
A. load on the motor
B. d.c. excitation only
C. both the speed and rotor flux
D. none of the above
Answer: B

92. A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed
A. the motor will stop
B. the motor continue to run in the same direction
C. the winding of the motor will burn
D. the motor will run in the reverse direction
E. none of the above
Answer: B

93. The magnitude of field flux in a 3-phase synchronous motor
A. remains constant at all loads
B. varies with speed
C. varies with the load
D. varies with power factor
Answer: A

94. The torque angle, in a synchronous motor, is the angle between
A. the supply voltage and the back e.m.f.
B. magnetising current and back e.m.f.
C. the rotating stator flux and rotor poles
D. none of the above
Answer: C

95. Hunting in a synchronous motor cannot be due to
A. windage friction
B. variable load
C. variable frequency
D. variable supply voltage
Answer: A

96. By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
A. By changing the supply frequency
B. By interchanging any two phases
C. By changing the applied voltage
D. By changing the load.
Answer: A

97. In a synchronous motor, V-curves represent relation between
A. armature current and field current
B. power factor and speed
C. field current and speed
D. field current and power factor
Answer: A

98. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be
A. 3000 r.p.m.
B. 1500 r.p.m.
C. 750 r.p.m.
D. none of the above
Answer: B

99. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have
A. no change of power factor
B. lagging power factor with over-excitation
C. leading power factor with under-excitation
D. leading power factor with over-excitation
Answer: D

100. Which of the following motors is non-self starting ?
A. D.C. series motor
B. synchronous motor
C. Squirrel cage induction motor
D. Wound round induction motor
Answer: B

101. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
A. the motor is said to be fully loaded
B. the torque generated is maximum
C. the excitation is said to be zero per cent
D. the excitation is said to be hundred per cent
Answer: D

102. In a synchronous motor, the damping winding is generally used to
A. prevent hunting and provide the starting torque
B. reduce the eddy currents
C. provide starting torque only
D. reduce noise level
E. none of the above
Answer: A

103. If the field of a synchronous motor is underexcited, the power factor will be
A. zero
B. unity
C. lagging
D. leading
Answer: C

104. The back e.m.f. in the stator of a synchronous motor depends on
A. number of poles
B. flux density
C. rotor speed
D. rotor excitation
E. none of the above
Answer: D

105. The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as
A. slip torque
B. pull-out torque
C. breaking torque
D. synchronising torque
Answer: D

106. In a synchronous motor, the armature current has large values for
A. high excitation only
B. low excitation only
C. both high and low excitation
D. none of the above
Answer: C

107. Which of the following losses, in a synchronous motor, does not vary with load?
A. Windage loss
B. Copper losses
C. Any of the above
D. None of the above
Answer: A

108. The size of a synchronous motor decreases with the increase in
A. flux density
B. horse power rating
C. speed
D. all of the above
Answer: A

109. Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?
A. Eddy current losses in the conductors
B. Iron losses in the stator
C. Copper losses in the slot portion of the conductors
D. Windage losses
E. None of the above
Answer: D

110. The duration of sudden snort-circuit test on a synchronous motor is usually about
A. one hour
B. one minute
C. one second
D. none of the above
Answer: C

111. The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as
A. pull-up torque
B. pull-in torque
C. pull-out torque
D. none of the above
Answer: B

112. A synchronous machine with low value of short-circuit ratio has
A. lower stability limit
(6) high stability limit
C. good speed regulation
D. good voltage regulation
E. none of the above
Answer: A

113. The construction of a synchronous motor resembles
A. a series motor
B. an induction motor
C. an alternator
D. a rotary converter
Answer: C

114. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will
A. stop
B. run as induction motor
C. function as static condenser
D. burn with dense smoke
Answer: A

115. For power factor correction, synchronous motors operate at
A. no-load and greatly over-excited fields
B. no-load and under-excited fields
C. normal load with minimum excitation
D. normal load with zero excitation
Answer: A

116. The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as
A. locked-rotor torque
B. synchronous torque
C. pull up torque
D. reluctance torque
Answer: A

117. Exciters of synchronous machines are
A. d.c. shunt machines
B. d.c. series machines
C. d.c. compound machines
D. any of the above
Answer: A

118. The coupling angle or load angle of synchronous motor is defined as the angle between the
A. rotor and stator teeth
B. rotor and the stator poles of opposite polarity
C. rotor and the stator poles of the same polarity
D. none of the above
Answer: B

119. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
A. the stator current will be zero
B. the stator current will be very small
C. the stator current will be very high
D. the back e.m.f. will be more than the supply voltage
E. none of the above
Answer: A

120 The armature current of the synchronous motor
A. has large values for low excitation i niy
B. has large values for high excitation only
C. has large values for low and high excitation
D. any of the above
Answer: C

121. The maximum power developed in a synchronous motor will depend on
A. the rotor excitation only
B. the supply voltage only
C. the rotor excitation and supply volt-age both
D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)
E. none of the above
Answer: D

122. A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as
A. static condenser
B. condenser
C. synchronous condenser
D. none of the above
Answer: C

129. A synchronous motor develops maximum power when load angle is
A. 45°
B. 60°
C. 90°
D. 120°
Answer: C

130. In a synchronous motor, the breakdown torque is
A. directly proportional to applied voltage
B. directly proportional to the square of the applied voltage
C. inversely proportional to applied voltage
D. none of the above
Answer: A