EEE MCQ (D.C Motors)

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D.C Motors Multiple Choice Questions and Answers Preparation for Competition exams

1.    No-load speed of which of the following motor will be highest ?
(a)     Shunt motor    
(b)     Series motor
(c)    Cumulative compound motor
(d)    Differentiate compound motor
Ans: b
2.    The direction of rotation of a D.C. series motor can be changed by
(a)     interchanging supply terminals
(b)     interchanging field terminals
(c)    either of (a) and (b) above
(d)    None of the above
Ans: b

3. Which of the following application requires high starting torque ?
(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive
(d) Air blower
Ans: c

4.    If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
(a)     Series motor
(b)     Shunt motor
(c)    Differentially compound motor
(d)    Cumulative compound motor
Ans: a

5.    Which D.C. motor will be preferred for machine tools ?
(a)    Series motor
(b)    Shunt motor   
(c)    Cumulative compound motor
(d)    Differential compound motor
Ans: b

6.    Differentially compound D.C. motors can find applications requiring
(a)    high starting torque
(b)    low starting torque
(c)     variable speed
(d)    frequent on-off cycles
Ans: b

7.    Which D.C. motor is preferred for elevators ?
(a)    Shunt motor
(b)    Series motor
(c)    Differential compound motor
(d)    Cumulative compound motor
Ans: d

8.    According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of
(a)     current in the conductor aovtaat of conductor
(c)    resultant force on conductor
(d)    none of the above
Ans: a

9.    If the field of a D.C. shunt motor gets opened while motor is running
(a) the speed of motor will be reduced %
(b) the armature current will reduce
(c)  the motor will attain dangerously high speed 1     
(d) the motor will continue to nuvat constant speed
Ans: c

10.    Starters are used with D.C. motors because
(a)    these motors have high starting torque
(b)    these motors are not self-starting
(c)    back e.m.f. of these motors is zero initially
(d)    to restrict armature current as there is no back e.m.f. while starting
Ans: d

11.    In D.C.  shunt motors as load is reduced
(a)    the speed will increase abruptly
(b)    the speed will increase in proportion to reduction in load
(c)    the speed will remain almost/constant
(d)    the speed will reduce
Ans: c

12.    A D.C. series motor is that which
(a)    has its field winding consisting of thick wire and less turns
(b)    has a poor torque
(c)    can be started easily without load
(d)    has almost constant speed
Ans: a

13.    For starting a D.C. motor a starter is required because
(a)    it limits the speed of the motor
(b)    it limits the starting current to a safe value
(c)    it starts the motor
(d)    none of the above
Ans: b

14.    The type of D.C. motor used for shears and punches is
(a)    shunt motor
(b)    series motor
(c)    differential compoutid D.C. motor
(d)    cumulative compound D.C. motor
Ans: d

15.    If a D.C. motor is connected across the A.C. supply it will
(a)     run at normal speed
(b)     not run
(c)    run at lower speed
(d)    burn due to heat produced in the field winding by .eddy currents
Ans: d

16.    To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
(a)    Ward Leonard control
(b)    rheostatic control
(c)    any of the above method
(d)    none of the above method
Ans: a

17.    When two D.C. series motors are connected in parallel, the resultant speed is
(a)    more than the normal speed
(b)    loss than the normal speed
(c)    normal speed
(d)    zero
Ans: c

18.    The speed of a D.C. shunt motor more than its full-load speed can be obtained by
(a)    decreasing the field current
(b)    increasing the field current
(c)    decreasing the armature current
(d)    increasing the armature current
Ans: a

19.    In a D.C. shunt motor, speed is
(a)    independent of armature current
(b)    directly  proportional  to  the armature current
(c)    proportional to the square of the current
(d)     inversely proportional to the armature current
Ans: a

20. A direct on line starter is used: for starting motors
(a)    iip to 5 H.P.
(b)    up to 10 H.P.
(c)    up to 15 H.P.
(d)    up to 20 H.P.
Ans: a

21.    What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
(a)    The motor will stop
(b)    The motor will continue to run
(c)    The armature may burn
(d)    The motor will run noisy
Ans: c

22.    In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
(a)    back e.m.f. is equal to armature drop
(b)    armature drop is negligible
(c)    flux is proportional to armature current
(d)    flux is practically constant in D:C. shunt motors
Ans: d

23.    In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(a)    almost negligible
(b)    rated full-load current
(c)    less than full-load current
(d)    more than full-load current
Ans: d

24.    These days D.C. motors are widely used in
(a)    pumping sets
(b)    air compressors
(c)    electric traction
(d)    machine shops
Ans: c

25.    By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(a)    Frame
(b)    Shaft
(c)    Commutator
(d)    Stator
Ans: c

26.    In which of the following applications D.C. series motor is invariably tried?
(a)    Starter for a car
(b)    Drive for a water pump
(c)    Fan motor
(d)    Motor operation in A.C. or D.C.
Ans: a

27.    In D.C. machines fractional pitch winding is used
(a)     to improve cooling
(b)     to reduce copper losses
(c)    to increase the generated e.m.f.
(d)    to reduce the sparking
Ans: d

28.    A three point starter is considered suitable for
(a) shunt motors
(b) shunt as well as compound motors
(c) shunt, compound and series motors
(d) all D.C. motors
Ans: b

29.    In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
(a)     100%
(b)     around 90%
(c)    anywhere between 75% and 90%
(d)    less than 50%
Ans: d

30.    The ratio of starting torque to full-load torque is least in case of
(a)    series motors
(b)    shunt motors
(c)    compound motors
(d)    none of the above
Ans: b

32.    In D.C. motor which of the following can sustain the maximum temperature rise?
(a)    Slip rings
(b)    Commutator
(c)    Field winding
(d)    Armature winding
Ans: c

33.    Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
(a)    Lenz's law
(b)    Faraday's law
(c)    Coloumb's law
(d)    Fleming's left-hand rule
Ans: d

34.    Which of the following load normally needs starting torque more than the rated torque?
(a)    Blowers
(b)    Conveyors
(c)    Air compressors
(d)    Centrifugal pumps
Ans: b

35.    The starting resistance of a D.C. motor is generally
(a)    low
(b)    around 500 Q
(c)    1000 Q
(d)    infinitely large
Ans: a

36.    The speed of a D.C. series motor is
(a)    proportional to the armature current
(b)    proportional to the square of the armature current
(c)    proportional to field current
(d)    inversely proportional to the armature current
Ans: d

37.    In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal
to
(a)    100% of the previous value
(b)    50% of the previous value
(c)    25% of the previous value
(d)    10% of the previous value
(e)    none of the above
Ans: c

38.    The current drawn by the armature of D.C. motor is directly proportional to
(a)    the torque required
(b)    the speed of the motor
(c)    the voltage across the terminals
(d)    none of the above
Ans: a

39.    The power mentioned on the name plate of an electric motor indicates
(a)    the power drawn in kW
(b)    the power drawn in kVA
(c)    the gross power
(d)    the output power available at the shaft
Ans: d

40.    Which D.C. motor has got maximum self loading property?
(a)     Series motor
(b)     Shunt motor
(c)    Cumulatively compounded 'motor
(d)    Differentially compounded motor
Ans: d

41.    Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
(a)    Series motor
(b)    Shunt motor
(c)    Cumulatively compounded motor
(d)    Differentially compounded motor
Ans: c

42.    If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
(a) nothing will happen to th£ motor
(b) this will make armature to take heavy current, possibly burning it
(c) this will result in excessive speed, possibly destroying armature due  to  excessive centrifugal stresses (d) motor will run at very slow speed
Ans: c

43.    D.C. series motors are used
(a) where load is constant
(b) where load changes frequently
(c) where constant operating speed is needed
(d) in none of the above situations.
Ans: d

44.    For the same H.P. rating and full load speed, following motor has poor starting torque
(a) shunt   
(b) series
(c) differentially compounded
(d) cumulativelyc'ompounded
Ans: c

45.    In case of conductively compensated D.C. series motors, the compensating winding is provided
(a)     as separately wound unit
(6)     in parallel with armature winding
(c)    in series with armature winding
(d)    in parallel with field winding
Ans: c

46.    Sparking at the commutator of a D.C. motor may result in
(a)     damage to commutator segments
(b)     damage to commutator insulation
(c)    increased power consumption
(d)    all of the above
Ans: d

47.    Which of the following motor is preferred for operation in highly explosive atmosphere ?
(a)     Series motor
(b)     Shunt motor
(c)    Air motor
(d)    Battery operated motor
Ans: c

48.    If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
(a)     Starting torque
(b)     Operating speed
(c)    Full-load current
(d)    All of the above
Ans: c

49.    Which one of the following is not the function of pole shoes in a D.C. machine ?
(a)     To reduce eddy current loss
(b)     To support the field coils
(c)    To spread out flux for better unifor-mity
(d)    To reduce the reluctance of the mag-netic path
Ans: a

50.    The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
(a) 4.0   
(b) 2.0
(c) 1.0   
(d) 0.5
Ans: d

51.    The condition for maximum power in case of D.C. motor is
(a)     back e.m.f. = 2 x supply voltage
(b)     back e.m.f. = | x supply voltage
(c)    supply voltage = | x back e.m.f.
(d)    supply voltage = back e.m.f.
Ans: b

52.    For which of the following applications a D.C. motor is preferred over an A.C. motor ?
(a)    Low speed operation
(b)    High speed operation
(c)    Variable speed operation
(d)    Fixed speed operation
Ans: c

53.    In D.C. machines the residual magnetism is of the order of
(a) 2 to 3 per cent
(6) 10 to 15 per cent
(c) 20 to 25 per cent
(d) 50 to 75 per cent
Ans: a

54.    Which D.C. motor is generally preferred for cranes and hoists ?
(a) Series motor    
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a

55.    Three point starter can be used for
(a)    series motor only
(b)    shunt motor only
(c)    compound motor only
(d)    both shunt and compound motor
Ans: d

56.    Sparking, is discouraged in a D.C. motor because
(a)    it increases the input power con-sumption
(b)    commutator gets damaged
(c)    both (a) and (b)
(d)    none of the above
Ans: b

57.    Speed control by Ward Leonard method gives uniform speed variation
(a)    in one direction
(b)    in both directions
(c)    below normal speed only
(d)    above normal speed only.
Ans: b

58.    Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have
to be
(a)     level compounded
(b)     under compounded
(c)    cumulatively compounded
(d)    differentially compounded
Ans: c
59.    Following motor is used where high starting torque and wide speed range control is required.
(a)     Single phase capacitor start
(b)     Induction motor
(c)    Synchronous motor
(d)    D.C. motor
(e)    None of the above
Ans: d

60.    In a differentially compounded D.C. motor, if shunt field suddenly opens
(a) the motor will first stop and then run in opposite direction as series motor
(b) the motor will work as series motor and run at slow speed in the same direction
(c)    the motor will work as series motor and run at high speed in the same direction
(d)    the motor will not work and come to stop
Ans: a

61.    Which of the following motor has the poorest speed regulation ?
(a)     Shunt motor   
(b)     Series motor
(c)    Differential compound motor
(d)    Cumulative compound motor
Ans: b

62.    Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
(a)     D.C. series motor
(b)     D.C. shunt motor
(c)    induction motor
(d)    all of above motors
Ans: a

63.    As -the load is increased the speed of D.C. shunt motor will
(a)     reduce slightly
(b)     increase slightly
(c)    increase proportionately
(d)    remains unchanged
Ans: a

64.    The armature torque of the D.C. shunt motor is proportional to
(a)    field flux only
(b)    armature current only
(c)    both (a) and (b)
(d)    none of the above
Ans: b

65.    Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
(a)    Voltage control method
(b)    Field control method
(c)    Armature control method
(d)    All above methods
Ans: c

66.    Usually wide and sensitive speed control is desired in case of
(a)     centrifugal pumps
(b)     elevators
(c)    steel rolling mills
(d)    colliery winders
Ans: d

67.    The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
(a) 2.36%   
(6) 4.76%
(c) 6.77%   
(d) 8.84%
Ans: b

68.    The armature voltage control of D.C. motor provides
(a)    constant torque drive
(b)    constant voltage drive
(c)    constant current drive
(d)    none of the above
Ans: a

69.    As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit
(a)     a resistance is connected in series with armature
(b)     a resistance is connected parallel to the armature
(c)    armature is temporarily open circuited
(d)    a high value resistor is connected across the field winding
Ans: a
70.    The speed of a D.C. shunt motor can be increased by
(a)    increasing the resistance in armature circuit
(b)    increasing the resistance in field circuit
(c)    reducing the resistance in the field circuit
(d)    reducing the resistance in the armature circuit
Ans: b

71.    If I2 be the armature current, then speed of a D.C. shunt motor is
(a)    independent of Ia
(b)    proportional to la
(c)    varies as (Ia)
(d)    varies as la
Ans: a

72.    In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
(a)     remain unchanged
(6)     reduce to one-fourth value
(c)    increase four folds
(d)    be doubled
Ans: a

73.    At the instant of starting when a D.C. motor is put on supply, it behaves like
(a)     a highly resistive circuit
(6)     a low resistance circuit
(c)    a capacitive circuit
(d)    none of the above
Ans: b

74.    The speed of a D.C. motor can be varied by varying
(a)     field current    
(b)     applied voltage
(c)    resistance in series with armature
(d)    any of the above
Ans: d

75.    Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
(a)    Low cost
(b)    Wide speed range
(c)    Stability
(d)    High starting torque.
Ans: a

76.    For a D.C. shunt motor if the excitation is changed
(a)     torque will remain constant
(b)     torque will change but power will remain constant
(c)    torque and power both will change
(d)    torque, power and speed, all will change
Ans: b

77.    Which motor has the poorest speed control?
(a) Differentially compounded motor
(b) Cumulatively compounded motor
(c) Shunt motor     
(d) Series motor
Ans: d

78.    The plugging gives the
(a)     zero torque braking
(b)     smallest torque braking
(c)    highest torque braking
(d)    none of the above
Ans: c

79.    The armature voltage control of D.C. motor provides
(a)     constant voltage drive
(b)     constant current drive
(c)    constant torque drive
(d)    none of the above
Ans: c

80.    If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor
(a)     of lower H.P. should be selected
(6)     of higher H.P. should be selected
(c)    can be used for 50°C ambient temperature also
(d)    is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor
Ans: d

81.    If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
(o)     regenerative    
(b)     plugging
(c)    dynamic braking
(d)    none of the above
(e)    any of the above
Ans: b

82.    Which of the following motors one will choose to drive the rotary compressor ?
(a)    D.C. shunt motor
(b)    D.C. series motor
(c)    Universal motor
(d)    Synchronous motor
Ans: d

83.    If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
(a) increase   
(b) decrease
(c) remain same    
(d) become zero
Ans: a

84.    Why are the D.C. motors preferred for traction applications ?
(a)    Torque and speed are inversely proportional to armature current
(b)    Torque is proportional to armature current
(c)    Torque is proportional to square root of armature current
(d)    The speed is inversely proportional to the torque and the torque is proportional to square of armature current
Ans: d

85.    Which of the following motors is usually used in house-hold refrigerators ?
(a)     D.C. shunt motor
(b)     D.C. series motor
(c)    Single phase induction motor (split phase start or induction run motor)
(d)    Reluctance motor
(e)    Synchronous motor
Ans: c

86.    Which of the following motors is most suitable for signalling devices and many kinds of timers ?
(a)    D.C. shunt motor
(b)    D.C. series motor
(c)    Induction motor
(d)    Reluctance motor
Ans: d

87.    Which motor should not be started on no-load ?
(a) Series motor    
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor.
Ans: a

88.    Ward-Leonard control is basically a
(a) voltage control method
(b) field divertor method
(c) field control method
(d) armature resistance control method
Ans: a

89.    For constant torque drive which speed control method is preferred ?
(a) Field control
(b) Armature voltage control
(c) Shunt armature control
(d) Mechanical loading system
Ans: b

90.    In Ward-Leonard control  the lower limit of speed is imposed by
(a)    residual magnetism of the generator
(b)    core losses of motor
(c)    mechanical losses of motor and gen¬erator together
(d)    all of the above
Ans: a

91.    The main disadvantage of the Ward-Leonard control method is
(a)    high initial cost
(b)    high maintenance cost
(c)    low efficiency at Hght loads
(d)    all of the above
Ans: d

92.   Regenerative method of braking is based on that
(a)    back e.m.f. is less than the applied voltage
(b)    back e.m.f. is equal to the applied voltage
(c)    back e.m.f. of rotor is more than the applied voltage
(d)    none of the above
Ans: b

93.    The hysteresis loss in a D.C. machine least depends on
(a)    Frequency of magnetic reversals
(b)    Maximum value of flux density
(c)    Volume and grade of iron
(d)    Rate of flow of ventilating air
Ans: d

94.    In a D.C. generator all of the following could be the effects of iron losses except
(a)     Loss of efficiency
(b)     Excessive heating of core
(c)    Increase in terminal voltage
(d)    Rise in temperature of ventilating air
Ans: c

95.    The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
(a)     hysteresis loss
(b)     field copper loss
(c)    armature copper loss
(d)    eddy current loss
Ans: c

96.    Which of the following loss in a D.C. generator varies significantly with the load current ?
(a)    Field copper loss   
(b)    Windage loss
(c)    Armature copper loss
(d)    None of the above
Ans: c
97.    Torque developed by a D.C. motor depends upon
(a)    magnetic field
(b)    active length of the conductor
(c)    current flow through the conductors
(d)     number of conductors
(e)    radius of armature
(f)     all above factors
Ans: f

98.    D.C. shunt motors are used for driving
(a) trains   
(b) cranes
(c) hoists   
(d) machine tools
Ans: d

99.    In a manual shunt motor starter
(a)     over load relay is connected in series and no volt relay in parallel with the load
(6)     over load relay is connected in paral¬lel and no volt relay in series with the load
(c)    over load relay and no volt relay are both connected in series with the load
(d)    over load relay and no volt relay are both connected in parallel with the load
Ans: a

100.    Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
(a)    Providing laminations in armature core
(b)    Providing laminations in stator
(c)    Using non-magnetic material for frame
(d)    Using material of low hysteresis co-efficient for armature core material
Ans: d

101. Which of the following loss in a D.C. generator is dissipated in the form of heat?
(a)    Mechanical loss
(b)    Core loss
(c)    Copper loss       
(d)    All of the above
Ans: d

102. Which of the following losses are significantly reduced by laminating the core of a D.C. generator?
(a) Hysteresis losses
(b) Eddy current losses
(c) Copper losses
(d) Windage losses
Ans: b

103.    The total losses in a well designed D.C. generator of 10 kW will be nearly
(a) 100 W   
(b) 500 W
(c) 1000 W   
(d) 1500 W
Ans: b

104.    The condition for maximum efficiency for a D.C. generator is
(a)    eddy current losses = stray losses
(b)    hysteresis losses = eddy current losses
(c)    copper losses = 0
(d)    variable losses = constant losses
Ans: d

105.    D.C. generators are normally designed for maximum efficiency around
(a) full-load   
(b) rated r.p.m.
(c) rated voltage    
(d) all of the above
Ans: a

106.    In a D.C. generator, the iron losses mainly take place in
(a)     yoke   
(b)     commutator
(c)    armature conductors
(d)    armature rotor
Ans: d

107.    D.C. generators are installed near the load centres to reduce
(a) iron losses   
(b) line losses
(c) sparking   
(d) corona losses
Ans: b

108.    The purpose of retardation test on D.C. shunt machines is to find out
(a)    stray losses 
(b)    eddy current losses
(c)    field copper losses
(d)     windage losses
Ans: a

109.    Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?
(a)    Swinburne's test
(b)    Hopkinson's test
(c)    Field test   
(d)     Brake test
Ans: c

110.    Hopkinson's test on D.C. machines is conducted at
(a) no-load   
(b) part load
(c) full-load   
(d) overload
Ans: c

111.    During rheostat braking of D.C. series motors
(a)    motor is run as a generator
(b)    motor is reversed in direction
(c)    motor is run at reduced speed
Ans: a

112.    For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors   
(b) Series motors
(c) Compound motors
(d) All of the above
Ans: d

113.    Which method of braking is generally used in elevators ?
(a)    Plugging
(b)    Regenerative braking
(c)    Rheostatic braking
(d)    None of the above
Ans: a

114.    In variable speed motor
(a)    a stronger commutating field is needed at low speed than at high speed
(b)    a weaker commutating field is needed at low speed than at high speed
(c)    same commutating field is needed at low speed than at high speed
(d)    none of the above is correct
Ans: b

115.    When the armature of a D.C. motor rotates, e.m.f. induced is
(a)    self-induced e.m.f.
(b)    mutually induced e.m.f.
(c)    back e.m.f.
(d)    none of the above
Ans: c

116.    Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
(a)    drum type controller is used
(b)    three point starter is used
(c)    four point starter is used
(d)    all above can be used
Ans: a

117.    If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a)     this will make armature to take heavy current, possibly burning it
(6)     this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
(c)    nothing will happen to motor
(d)    motor will come to stop
Ans: a
118.    D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short
duration. We will select the
(a)     series motor     
(b)     shunt motor
(c)    compound motor
(d)    any of the above
Ans: a

119.    D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
(a)     series motor     
(b)     shunt motor
(c)    compound motor
(d)    any of the above
Ans: c

120.    Which D.C. motor has got maximum self relieving property ?
(a) Series motor    
(6) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a

121.    In the D.C. motor the iron losses occur in
(a) the field   
(b) the armature
(c) the brushes      
(d) the commutator
Ans: b

122.    The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by
(a)     reducing the field current
(b)     decreasing the armature current
(c)    increasing the armature current
(d)    increasing the excitation current
(e)    none of the above methods
Ans: a

123.    One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
(a)    runs as a generator
(b)    does not run as a generator
(c)    also runs as a motor comes to stop after sometime
Ans: a

EEE MCQ (A.C Fundamentals)

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

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

Ans: a

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

Ans: c

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

Ans: b

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

Ans: b

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

Ans: d

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

EEE MCQ (D.C. Generators )

Preparation for Engineering

Bottom of Form

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

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

Ans: c

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

Ans: c

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

Ans: d

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

Ans: d

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

Ans: b

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

Ans: a

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

Ans: c

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

Ans: b

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

Ans: b

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

Ans: b

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

Ans: d

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

Ans: a

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

Ans: d

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

Ans: b

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

Ans: b

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

Ans: b

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

Ans: a

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

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

Ans: d

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

Ans: c

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

Ans: b

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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