[PDF Notes] What is Lipsey’s Theory of Phillips Curve?

Lipsey in 1960 provided a sound theoretical basis for the statistical relation observed by Phillips. He argued that the observed inverse relationship between wage inflation and unemployment can be derived from two behavioural relations:

(a) A positive relation between the rate of money wage change and the magnitude for excess demand for labour and

(b) An inverse non-linear relation between excess labour demand and unemploy­ment. These relations refer to a single micro labour market.

1. Relation between Wage Inflation and Excess Demand:

Lipsey assumed that wage inflation (w) is an increasing function of the proportionate excess demand for labour.

At the origin, excess demand is zero and as a result wage inflation will be zero. To the right of the origin, excess demand is positive so that money wages will be rising. To the left of the origin, excess demand is negative or there exists excess supply and as a result, money wages will be falling.

2. Relation between Excess Demand and Unemploy­ment:

The negative relation implies that greater the excess demand, the lower will be the level of unemployment and vice versa. When excess demand is zero the labour market is in equilibrium. But this does not indicate the absence of unemployment.

Lipsey measured the excess demand for labour by only the excess of number of vacancies over the number of the un­employed. Thus, zero excess demand for labour can occur at positive unemployment rate.

The unemployment com­patible with zero excess demand is called frictional un­employment (uf). Frictional unemployment arises because the process of matching vacancies with unemployed workers is not instantaneous.

The non-linear relation implies that while positive ex­cess demand for labour will decrease the unemployment rate below frictional level (uf), it can never fall below zero however high is the level of excess demand.

By combining these two relations, Lipsey obtained the Phillips curve relating the level of unemployment with wage inflation.

300+ TOP D.C. MOTORS MCQs and Answers Quiz

D.C. Motors Multiple Choice Questions | dc motor mcqs

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

Answer: 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

Answer: B

3. Which of the following application requires high starting torque ?
A. Lathe machine
B. Centrifugal pump
C. Locomotive
D. Air blower

Answer: 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

Answer: 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

Answer: 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

Answer: B

7. Which D.C. motor is preferred for elevators ?
A. Shunt motor
B. Series motor
C. Differential compound motor
D. Cumulative compound motor

Answer: 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

Answer: 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

Answer: 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

Answer: D

D.C. MOTORS MCQs

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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: A

20. A direct on line starter is used: for starting motors
A. up to 5 H.P.
B. up to 10 H.P.
C. up to 15 H.P.
D. up to 20 H.P.

Answer: 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

Answer: 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

Answer: 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

Answer: D

24. These days D.C. motors are widely used in
A. pumping sets
B. air compressors
C. electric traction
D. machine shops

Answer: 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

Answer: 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.

Answer: 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

Answer: 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

Answer: 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%

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: B

35. The starting resistance of a D.C. motor is generally
A. low
B. around 500 Q
C. 1000 Q
D. infinitely large

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: D

41. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?
A. Series motor
B. Shunt motor
C. Cumulatively compounded motor
D. Differentially compounded motor

Answer: 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 the 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

Answer: 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.

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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 uniformity
D. To reduce the reluctance of the magnetic path

Answer: 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

Answer: 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.

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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.

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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%

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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.

Answer: 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

Answer: B

77. Which motor has the poorest speed control?
A. Differentially compounded motor
B. Cumulatively compounded motor
C. Shunt motor
D. Series motor

Answer: D

78. The plugging gives the
A. zero torque braking
B. smallest torque braking
C. highest torque braking
D. none of the above

Answer: 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

Answer: 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 recommended by manufacturer and select the next higher H.P. motor

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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.

Answer: 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

Answer: 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

Answer: 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 generator together
D. all of the above

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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 parallel 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: A

106. In a D.C. generator, the iron losses mainly take place in
A. yoke
B. commutator
C. armature conductors
D. armature rotor

Answer: D

107. D.C. generators are installed near the load centres to reduce
A. iron losses
B. line losses
C. sparking
D. corona losses

Answer: 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

Answer: 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

Answer: C

110. Hopkinson’s test on D.C. machines is conducted at
A. no-load
B. part load
C. full-load
D. overload

Answer: 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

Answer: 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

Answer: D

113. Which method of braking is generally used in elevators ?
A. Plugging
B. Regenerative braking
C. Rheostatic braking
D. None of the above

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: 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

Answer: A

121. In the D.C. motor the iron losses occur in
A. the field
B. the armature
C. the brushes
D. the commutator

Answer: 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

Answer: 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

Answer: A

[PDF Notes] What are the main Demerits of Phillips Curve?

The simple Phillips curve analysis suggesting a stable and permanent trade off between the prices (or wage) inflation and unemployment has been found unsatisfactory because of the following reasons:

1. Unstable Trade off:

The Phillips curve is of little value because it is unstable and not permanent. The relationship between inflation rate and unemployment rate not only varies widely across the countries but also is not stable within a given country through time.

Thus, the fact is that there exists no simple relationship between the rate of inflation and the rate of unemployment and the Phillips curve loses its explanatory power.

2. Role of Trade Unions Ignored:

Lipsy did not recognise the role of trade unions in influencing wages. The trade unions interfere in the labour market. A decrease in the unemployment rate raises the market power of the organised labour which then is used to raise wages.

This additional factor also determines the shape and position of the Phillips curve and is responsible for the shifts in the curve.

3. Influence of Cost of Living Ignored:

There is two-way relationship between wages and prices. Wages as a major element in the cost of production influence prices. But the prices through their impact on cost of living also influence wages.

The Phillips curve model considers only the effect of wages on prices and ignores the effect of prices on wages. Increase in prices causes increase in the cost of living which leads to an increase in wages.

Workers have to be compensated for a rising cost of living, whether these higher wages are negotiated with the trade unions or administered by the employer.

But this change in wages as a result of change in prices causes shifts in the Phillips curve and makes it unstable.

4. The Problem of Stagflation:

The Phillips curve which says that inflation and unemployment vary inversely remained popular during 1960s.

But, since about 1967 onwards, the major industrialised countries of the world have been experiencing high rate of inflation accompanied by a high rate of unemployment.

This new phenomenon, which is termed as stagflation, has led to the breakdown of Phillips curve and it has lost its explanatory power

5. Inflation an International Phenomenon:

The Phillips curve analysis assumes inflation as the internal problem of a country and relates it with the domestic labour market.

It ignores the fact that inflation in modern times is an international phenomenon and the domestic variables do not have much influence on it

6. Neglect of Macro Issues:

Lipsy’s analysis does not provide answer to certain macro problems: (a) it does not tell what determines the level of employment beyond which further increases in the aggregate demand lead to rising prices; (b) it does not tell what determines the rate at which wages will increase at a certain level of unemployment.

7. Johnson’s Criticism:

H.G. Johnson has criticised the Phillips curve on the following grounds:

(i) It does not provide any basic theoretical principle for the verification of which his study is to be quoted. It just assumes that the curve would have a curvilinear form and therefore it appears only a statistical artifact.

(ii) The theory behind the Phillips curve represents the crudest and least sophisticated possible economic explanation of the dynamics of economic markets in two senses:

(a) It assumes that the price adjustments in any specific market takes place with reference to the excess demand/supply in that market only and developments in other markets have no effect here.

(b) It assumes that the same theory is able to give the price adjustments in both absolute and relative terms, so that if any absolute increase in money wage takes place, it also implies a corresponding increase in wage level relative to other prices.

300+ TOP DC Generators MCQs and Answers Quiz

D.C. GENERATORS Multiple Choice Questions :-

1. Lamination’s of core are generally made of
A. case iron
B. carbon
C. silicon steel
D. stainless steel
Answer: C

2. Which of the following could be lamina-proximately the thickness of lamination’s of a D.C. machine ?
A. 0.005 mm
B. 0.05 mm
C. 0.5 m
D. 5 m
Answer: 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
Answer: D

5. The field coils of D.C. generator are usually made of
A. mica
B. copper
C. cast iron
D. carbon
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: D

12. The bearings used to support the rotor shafts are generally
A. ball bearings
B. bush bearings
C. magnetic bearmgs
D. needle bearings
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: A

18. A separately excited generator as compared to a self-excited generator
A. is amenable to better voltage control
B. is more stable
C. has exciting current independent of load current
D. has all above features
Answer: D

19. In case of D.C. machines, mechanical losses are primary function of
A. current
B. voltage
C. speed
D. none of above
Answer: C

20. Iron losses in a D.C. machine are independent of variations in
A. speed
B. load
C. voltage
D. speed and voltage
Answer: 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
Answer: A

23. Brushes of D.C. machines are made of
A. carbon
B. soft copper
C. hard copper
D. all of above
Answer: 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
Answer: 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
Answer: B

26. The material for commutator brushes is generally
A. mica
B. copper
C. cast iron
D. carbon
Answer: D

27. The insulating material used between the commutator segments is normally
A. graphite
B. paper
C. mica
D. insulating varnish
Answer: 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
Answer: 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 mag¬netisation
C. crossmagnetisation as well as demagnetising
D. cross magnetisation only
Answer: C

30. Armature reaction of an unsaturated D.C. machine is
A. crossmagnetising
B. demagnetising
C. magnetising
D. none of above
Answer: 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
Answer: 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
Answer: 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
Answer: B

35. Welding generator will have
A. lap winding
B. wave winding
C. delta winding
D. duplex wave winding
Answer: 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
Answer: 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
Answer: C

38. The function of pole shoes in the case of D.C. machine is
A. to reduce the reluctance of the mag¬netic 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
Answer: 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
Answer: D

40. A D.C. welding generator has
A. lap winding
B. wave moving
C. duplex winding
D. any of the above
Answer: 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 gen¬erators
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: A

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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: C

D.C. GENERATORS Objective Questions Pdf ::

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
Answer: D

62. Permeance is the reciprocal of
A. flux density
B. reluctance
C. ampere-turns
D. resistance
Answer: 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.
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: D

74. In a D.C. generator the critical resistance refers to the resistance of
A. brushes
B. field
C. armature
D. load
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: A

79. The following constitute short-circuit in the armature winding.
A. Insulation failure between two commutator 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
Answer: 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
Answer: A

82. A D.C. generator can be considered as
A. rectifier
B. primemover
C. rotating amplifier
D. power pump
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: B

87. An exciter for a turbo generator is a
A. separately excited generator
B. shunt generator
C. series generator
D. compound generator
Answer: 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 irrespective of the load
D. speed varies in proportion to the load on the generator
Answer: 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
Answer: 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
Answer: D

91. In over compounded generator, full load terminal voltage is
A. almost zero
B. less than no load terminal voltage
C. more than no load terminal voltage
D. equal to no-load terminal voltage
Answer: 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
Answer: 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
Answer: 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
Answer: 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. will be of 5 xiVHz
D. will be of v Hz 5
Answer: 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
Answer: 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
Answer: 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
Answer: A

99. Armature reaction in a generator results in
A. demagnetization of leading pole tip and magnetization of trailing pole tip
B. demagnetization of trailing pole tip and magnetization of leading pole tip
C. demagnetizing the center of all poles
D. magnetizing the center of all poles
Answer: 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:

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
Answer: C

102. The critical resistance of the D.C. generator is the resistance of
A. field
B. brushes
C. armature
D. load
Answer: A

103. When two D.C. series generators are running in parallel, an equalizer 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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 resistance in the field circuit
Answer: 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
Answer: 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
Answer: 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
Answer: 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 characteristics
D. same percentage regulation
Answer: C

114. When two D.C. generators are running in parallel an equalizer 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 cur¬rents to the load
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: B

119. For both lap and wave winding’s, there are as many commutator bars as the number of
A. slots
B. armature conductors
C. winding elements
D. poles
Answer: C

126. 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
Answer: D

127. 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
Answer: D

128. 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
Answer: C

129. 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 winding’s
C. unequal speed regulation of their prime movers
D. unequal series field resistances
Answer: A

130. 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 prime mover
D. check armature insulation resistance
Answer: A

D.C. GENERATORS Questions and Answers Free Download ::

[PDF Notes] Here is your short essay on Stagflation

During 1960s, Phillips curve remained popular among the economists and the policy-makers and there was general agreement that a stable and enduring trade-off existed between unemployment and inflation.

Since about 1967 onwards, the major industrialised countries of the world are experiencing simultaneous growth of inflation and unemployment.

This new phenomenon of the existence of high inflation coupled with high unemployment has been termed as stagflation.

The experience of stagflation runs counter to the prediction of the Phillips curve that there exists an inverse relationship between inflation and unemployment.

Diagrammatically, the phenomenon of stagflation leads to an upward shift in the Phillips curve indicating that a given level of unemployment is associated with higher rate of inflation.

Thus, the existence of inflation and unemploy­ment simultaneously has led to the collapse of Phillips curve trade-off, rendered the Phillips curve unstable and reduced its predictive power.

300+ A.C. Fundamentals, Circuits & Circuit Theory MCQs Answers

A.C. Fundamentals, Circuits and Circuit Theory Multiple Choice Questions

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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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 maxi¬mum value, the other will reach its minimum value
D. none of the above
Answer: 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
Answer: 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°
Answer: 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°
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: C

18. Form factor for a sine wave is
A. 1.414
B. 0.707
C. 1.11
D. 0.637
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: A

24. In a series resonant circuit, the impedance of the circuit is
A. minimum
B. maximum
C. zero
D. none of the above
Answer: A

25. Power factor of an electrical circuit is equal to
A. R/Z
B. cosine of phase angle difference be-tween current and voltage
C. kW/kVA
D. ratio of useful current to total cur¬rent Iw/I
E. all above
Answer: 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
Answer: 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
Answer: E

28. Capacitors for power factor correction are rated in
A. kW
B. kVA
C. kV
D. kVAR
Answer: 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
Answer: 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
Answer: 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
Answer: 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.
Answer: 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
Answer: 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
Answer: 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
Answer: 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 power
D. actual power is more than its reactive power
Answer: C

37. Power factor of the following circuit will be zero
A. resistance
B. inductance
C. capacitance
D. both B. and C.
Answer: D

38. Power factor of the following circuit will be unity
A. inductance
B. capacitance
C. resistance
D. both A. and B.
Answer: 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
Answer: 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
Answer: C

41. In a loss-free R-L-C circuit the transient current is
A. oscillating
B. square wave
C. sinusoidal
D. non-oscillating
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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°
Answer: 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
Answer: 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
Answer: 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
Answer: A

53. Which of the following circuit component opposes the change in the circuit voltage ?
A. Inductance
B. Capacitance
C. Conductance
D. Resistance
Answer:

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
Answer: A

55. Power factor of electric bulb is
A. zero
B. lagging
C. leading
D. unity
Answer: D

56. Pure inductive circuit takes power from the A.C. line when
A. applied voltage decreases but current increases
B. applied voltage increases but current decreases
C. both applied voltage and current increase
D. both applied voltage and current decrease
Answer: 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
Answer: 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
Answer: 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 resistance
C. increases with the increase of capacitance and decrease of resistance
D. increase with increase of capacitance and increase of resistance
Answer: 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, Land C
Answer: A

Circuit Theory Objective Questions Pdf ::

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
Answer: 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.LorC
E. R,LorC
Answer: 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
Answer: A

64. The time constant of a series R-C circuit is given by
A. R/C
B. RC2
C. RC
D. R2C
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: A

74. The ratio of active power to apparent power is known as factor.
A. demand
B. load
C. power
D. form
Answer: 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
Answer: 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
Answer: 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°
Answer: C

78. The purpose of a parallel circuit resonance is to magnify
A. current
B. voltage
C. power
D. frequency
Answer: 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
Answer: 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
Answer: 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
Answer: C

82. Skin effect occurs when a conductor carries current at_____ frequencies.
A. very low
B. low
C. medium
D. high
Answer: D

83. At ______ frequencies the parallel R-L circuit behaves as purely resistive.
A. low
B. very low
C. high
D. very high
Answer: 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
Answer: D

85. The power is measured in terms of decibles in case of
A. electronic equipment
B. transformers
C. current transformers
D. auto transformers
Answer: 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
Answer: 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
Answer: 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
Answer: D

89. Aphasoris
A. a line which represents the magnitude and phase of an alternating quantity
B. a line representing the magnitude and direction of an alternating quantity
C. a coloured tag or band for distinction between different phases of a 3-phase supply
D. an instrument used for measuring phases of an unbalanced 3-phase load
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: C

94. The frequency of domestic power supply in India is
A. 200 Hz
B. 100 Hz
C. 60 Hz
D. 50 Hz
Answer: 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
Answer: 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
Answer: B

97. Ohm is unit of all of the following except
A. inductive reactance
B. capacitive reactance
C. resistance
D. capacitance
Answer: D

98. The series and parallel resonance on L-C circuit’ differs in that
A. series resistance needs a low-resistance source for sharp rise in current
B. series resonance needs a high-resistance source for sharp increase in current
C. parallel resonance needs a low-resistance source for a sharp in¬crease in impedance
D. parallel resonance needs a low-resistance source for a sharp rise in line current
Answer: A

99. The phosphors for which of the following pair are 180° out of phase for VL, VC and VR?
A. Vc and VR
B. VL and VR
C. Vc and VL
D. none of the above
Answer: 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
Answer: 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
Answer: D

102. The power factor of a D.C. circuit is always
A. less than unity
B. unity
C. greater than unity
D. zero
Answer: 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
Answer: 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
Answer: 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
Answer: 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
Answer: B

118. 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
Answer: A

119. 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
Answer: B

120. 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
Answer: A

A.C. Fundamentals, Circuits & Circuit Theory objective questions with answers pdf download online exam test