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MCQOPTIONS
This section includes 378 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
A 240 V DC series motor takes 40 A when giving its rated torque at 1500 rpm, operating in the linear region of magnetization characteristics. If the armature and field resistance together is 0.3 Ω, then the value of resistance to be added to obtain rated torque at 1000 rpm is: |
| A. | 1.9 Ω |
| B. | 1.6 Ω |
| C. | 2.2 Ω |
| D. | 2.5 Ω |
| Answer» B. 1.6 Ω | |
| 52. |
Consider the following statements:The armature reaction mmf in a dc machine is:1. Stationery with respect to the field2. Rotating with respect to the field poles3. Rotating with respect to the armatureWhich of these statements are correct? |
| A. | 1, 2 and 3 |
| B. | 1 and 2 only |
| C. | 1 and 3 only |
| D. | 2 and 3 only |
| Answer» D. 2 and 3 only | |
| 53. |
A generator delivers 210 V on no load and 200 V on full load. The voltage regulation of the d.c. generator is |
| A. | 95% |
| B. | 5% |
| C. | 10% |
| D. | 4.76% |
| Answer» C. 10% | |
| 54. |
Following statements are given for DC motors(a) DC motors require less maintenance than AC motors(b) DC motors cannot provide high starting torque(c) DC motors are not suitable for very high-speed applications(d) The methods of speed control of DC motors are simpler and less expensive than those of AC motorsWhich of the following statements are correct? |
| A. | (a) and (c) |
| B. | (a) and (b) |
| C. | (b) and (c) |
| D. | (c) and (d) |
| Answer» E. | |
| 55. |
A d.c. series generator has a no load induced e.m.f. of 10 volts. If its speed is doubled, the no load induced e.m.f. is |
| A. | 20 volts |
| B. | 10 volts |
| C. | 5 volts |
| D. | zero volt |
| Answer» B. 10 volts | |
| 56. |
A generator is rated 2 kW 200 V D. C. It can supply load current of |
| A. | 4000 A |
| B. | 100 A |
| C. | 10 A |
| D. | 4 A |
| Answer» D. 4 A | |
| 57. |
A lap wound DC machine having 4-poles has 720 armature conductors. Its field winding is excited from a DC source to create an air-gap flux of 32 mWb/pole. The generator is run from a prime mover at 1500 rpm and supplies a current of 100 A to an electric load. Calculate the electromagnetic power developed in the machine? |
| A. | 50 kW |
| B. | 65.7 kW |
| C. | 76.5 kW |
| D. | 57.6 kW |
| Answer» E. | |
| 58. |
A four-pole, lap-would DC machine has 462 conductors in the armature. The average flux per pole is 0.02 Wb. Determine the induced armature voltage when the armature rotates at 1000 rpm. |
| A. | 154 V |
| B. | 196 V |
| C. | 120 V |
| D. | 180 V |
| Answer» B. 196 V | |
| 59. |
A generator has an open circuit emf of 18 V. Its terminal voltage drops to 15 V with a load resistance of 30 Ω. Calculate its internal resistance. |
| A. | 3 Ω |
| B. | 0.5 Ω |
| C. | 6 Ω |
| D. | 0.6 Ω |
| Answer» D. 0.6 Ω | |
| 60. |
______ is used as power source in electric arc welding. |
| A. | DC Series generator |
| B. | Differentially wound compound generator |
| C. | Separately excited DC generator |
| D. | Cumulative compound DC generator |
| Answer» C. Separately excited DC generator | |
| 61. |
In the case of the DC machine, the efficiency is maximum when |
| A. | Windage resistance = windage Reactance |
| B. | Fractional loss = copper Loss |
| C. | Copper loss in the armature circuit = constant loss |
| D. | Copper loss in the field circuit = constant Loss |
| Answer» D. Copper loss in the field circuit = constant Loss | |
| 62. |
A dc machine, having a symmetrical closed-circuit armature winding and a sinusoidal air-gap flux-density distribution, will have a sinusoidal voltage induced in the individual coils. The resultant brush-to-brush voltage will have a waveform |
| A. | Sinusoidal with the negative-half reversed |
| B. | Unidirectional and constant without any ripples |
| C. | Unidirectional and constant with ripples superimposed |
| D. | Sinusoidal positive-half and zero negative-half, in each cycle |
| Answer» D. Sinusoidal positive-half and zero negative-half, in each cycle | |
| 63. |
A dc power supply has no - load voltage of 30 V and a full load voltage of 25 V at full - load current of 1 A. Its output resistance and load regulation, respectively are |
| A. | 5 Ω and 20% |
| B. | 25 Ω and 20% |
| C. | 5 Ω and 16.7% |
| D. | 25 Ω and 16.7% |
| Answer» C. 5 Ω and 16.7% | |
| 64. |
In a DC machine, which of the following statement is true? |
| A. | Compensating winding is used for neutralizing armature reaction while inter pole winding is used for producing residual flux |
| B. | Compensating winding is used for improving commutation while inter pole winding is used for neutralizing armature reaction |
| C. | Compensating winding is used for improving commutation while inter pole winding is used for producing residual flux |
| D. | Compensating winding is used for neutralizing armature reaction while inter pole winding is used for improving commutation |
| Answer» E. | |
| 65. |
Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below:Statement (I): The electro-mechanical energy conversion principles are developed with the ‘field energy’, being magnetic or electric, as the basis.Statement (II): This approach can deal with only the steady-state analysis of the electro-mechanical energy conversion, but not the transient-state analysis. |
| A. | Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I |
| B. | Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I |
| C. | Statement I is true but Statement II is false |
| D. | Statement I is false but Statement II is true |
| Answer» D. Statement I is false but Statement II is true | |
| 66. |
If the residual magnetism of a DC shunt generator is destroyed accidentally, it may be restored by connecting its shunt field: |
| A. | in reverse |
| B. | to a DC source |
| C. | to an AC source |
| D. | to the earth |
| Answer» C. to an AC source | |
| 67. |
Identify the machine shown in the circuit. |
| A. | DC short shunt compound generator |
| B. | DC short shunt compound motor |
| C. | DC shunt motor |
| D. | DC long shunt compound generator |
| Answer» E. | |
| 68. |
In a DC generator, generated emf is directly proportional to _____ |
| A. | Armature current |
| B. | Pole flux |
| C. | Number of armature parallel paths |
| D. | All of the above |
| Answer» C. Number of armature parallel paths | |
| 69. |
A 220 V separately excited dc motor takes 20 A and the armature resistance is 1.0 Ω. If the armature constant KaΦ = 1.5 rad/sec, the speed of the motor is |
| A. | 1000 rpm |
| B. | 2000/π rpm |
| C. | 3000/π rpm |
| D. | 4000/π rpm |
| Answer» E. | |
| 70. |
A triangular mmf wave is produced in the air-gap of an electric machine. Such a wave is produced by. |
| A. | Stator of an induction machine |
| B. | Rotor of a synchronous machine |
| C. | Stator of a dc machine |
| D. | Rotor of a dc machine |
| Answer» E. | |
| 71. |
In a DC generator, sparking at the brushes occurs due to: |
| A. | distributed winding |
| B. | armature reaction and commutation |
| C. | high resistance of brushes |
| D. | improper connection of winding |
| Answer» C. high resistance of brushes | |
| 72. |
Direct current machines are attached with inter-poles in order to |
| A. | Increases the starting torque |
| B. | Improve commutation under loaded conditions |
| C. | Increase running torque |
| D. | Decrease windage loss |
| Answer» C. Increase running torque | |
| 73. |
Armature is the _____ part of DC machine |
| A. | Reciprocating |
| B. | Static |
| C. | Rotating |
| D. | Vibrating |
| Answer» D. Vibrating | |
| 74. |
In a DC generator, brushes are made of _______. |
| A. | copper |
| B. | aluminium |
| C. | carbon or graphite |
| D. | laminated steel |
| Answer» D. laminated steel | |
| 75. |
A 10 hp, 240 V dc shunt motor, having armature-circuit resistance of 0.5 Ω and a full-load current of 40 A, is started by a starter, such that sections of required resistances in series with the armature-circuit should limit the starting current to 150% of the full-load current. The steady-state emf developed by the machine at full-load when the arm of the starter is moved to the next step is |
| A. | 120 V |
| B. | 100 V |
| C. | 80 V |
| D. | 60 V |
| Answer» D. 60 V | |
| 76. |
Commutator motors have: |
| A. | Absolutely uniform torque |
| B. | Approximately uniform torque |
| C. | Non-uniform torque |
| D. | None of these |
| Answer» D. None of these | |
| 77. |
A dc shunt generator is delivering 20 kW at a terminal voltage of 200 V to a resistive load. The armature and shunt resistances are 0.5 Ω and 100 Ω respectively. Calculate the induced emf in the armature. (neglect brush voltage drop) |
| A. | 251 V |
| B. | 292 V |
| C. | 202 V |
| D. | 351 V |
| Answer» B. 292 V | |
| 78. |
If Ia = Armature Current,Ise = Series Field Current andIL = Load Current, then the relation then the relation between these currents for a DC series generator is _____. |
| A. | IL = Ise + Ia |
| B. | IL = Ise = Ia |
| C. | IL + Ise + Ia = 0 |
| D. | IL + Ise = Ia |
| Answer» C. IL + Ise + Ia = 0 | |
| 79. |
Induced emf in d.c. generator is directly proportional to |
| A. | armature speed |
| B. | number of machine poles |
| C. | flux per pole |
| D. | All of the above |
| Answer» E. | |
| 80. |
A 6 pole, wave connected DC armature has 250 conductors and runs at 1200 rpm. The emf generated is 600V. The useful Flux/pole is: |
| A. | 0.04 Wb |
| B. | 0.4 Wb |
| C. | 4.0 Wb |
| D. | 0.44 Wb |
| Answer» B. 0.4 Wb | |
| 81. |
Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below:Statement (I): The armature structures of all rotating machines are laminated in order to reduce the eddy-current losses.Statement (II): The armature windings of both the D.C. and A.C. machines have to deal with alternating currents only. |
| A. | Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I |
| B. | Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I |
| C. | Statement I is true but Statement II is false |
| D. | Statement I is false but Statement II is true |
| Answer» B. Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I | |
| 82. |
In a 4-pole dynamo, the flux/pole is 15 mWb. If the armature is driven at 600 rpm, the average emf induced in one of the armature conductors will be: |
| A. | 0.3 V |
| B. | 0.4 V |
| C. | 0.5 V |
| D. | 0.6 V |
| Answer» E. | |
| 83. |
A 6-pole, wave-wound armature has 600 conductors and is driven at 700 rpm. Determine the generated EMF in the armature if the flux per pole is 10 mWb. |
| A. | 420 V |
| B. | 230 V |
| C. | 500 V |
| D. | 210 V |
| Answer» E. | |
| 84. |
An ideal DC generator is one that has _____ voltage regulation |
| A. | Low |
| B. | High |
| C. | Zero |
| D. | Positive |
| Answer» D. Positive | |
| 85. |
If the voltage regulation of a dc generator is - 95% approximately then it is a |
| A. | DC shunt generator |
| B. | DC series generator |
| C. | Level compound generator |
| D. | Differentially compound generator |
| Answer» C. Level compound generator | |
| 86. |
A 4-pole d.c. generator runs at 750 rpm. and generates an emf. of 240 V. The armature is wave-wound and has 792 conductors. If the total flux from each pole is 0.0145 Wb, what is the leakage coefficient? |
| A. | 1.6 |
| B. | 1.8 |
| C. | 1.5 |
| D. | 1.2 |
| Answer» E. | |
| 87. |
In Electrical Machine if loose commutator bars are present it will set up: |
| A. | Electricity |
| B. | Eccentricity |
| C. | Humidity |
| D. | Connectivity |
| Answer» C. Humidity | |
| 88. |
In the case of DC machines, the brush contact drop is assumed to be _______ for carbon brushed. |
| A. | 0.5 V |
| B. | 0.1 V |
| C. | 2.0 V |
| D. | 1.0 V |
| Answer» D. 1.0 V | |
| 89. |
Aluminium is not used as winding wire for the armature of d. c. machine because |
| A. | Aluminium has low resistivity |
| B. | Of large winding space required by Aluminium conductor |
| C. | Of low thermal conductivity of Aluminium |
| D. | Of high cost of Aluminium |
| Answer» E. | |
| 90. |
Flat compound characteristic of a DC compound generator is obtained by connecting a: |
| A. | variable resistance in parallel with shunt load |
| B. | variable resistance across series field |
| C. | fixed resistance in parallel with shunt load |
| D. | fixed resistance across series field |
| Answer» C. fixed resistance in parallel with shunt load | |
| 91. |
A 4-pole DC motor is lap-wound with 400 conductors. The pole shoe is 20 cm long and the average flux density over one-pole pitch is 0.4 T, the armature diameter is 30 cm. When the motor is drawing 25 A and running at 1500 rpm, the torque developed will be nearly |
| A. | 30 Nm |
| B. | 40 Nm |
| C. | 50 Nm |
| D. | 60 Nm |
| Answer» B. 40 Nm | |
| 92. |
In DC generator on load, the air-gap flux distribution in space is |
| A. | Sinusoidal |
| B. | Triangular |
| C. | Pulsating |
| D. | Flat topped |
| Answer» E. | |
| 93. |
A field coil of a shunt motor has a resistance of 45 Ω at 20° C. Find the average temperature of the winding at the end of the run when the resistance is increased to 48 Ω. The temperature coefficient of resistance is 0.004/°C. |
| A. | 45° C |
| B. | 42° C |
| C. | 35° C |
| D. | 38° C |
| Answer» E. | |
| 94. |
A 4 – pole, separately excited, wave wound DC machine with negligible armature resistance is rated for 230 V and 5 kW at a speed if 1200 rpm. If the same armature coils are reconnected to forms a lap winding, what is the rated voltage (in volts) and power (in kW) respectively at 1200 rpm of the reconnected machine if the field circuit is left unchanged? |
| A. | 230 and 5 |
| B. | 115 and 5 |
| C. | 115 and 2.5 |
| D. | 230 and 2.5 |
| Answer» C. 115 and 2.5 | |
| 95. |
A shunt generator has a critical field resistance of 200 ohm at a speed of 800 rpm. If the speed of the generator is increased to 1000 rpm, what is the change in critical field resistance of the generator? |
| A. | Decrease to 160 ohm |
| B. | Remains the same at 200 ohm |
| C. | Increases to 250 ohm |
| D. | Increases to 312.5 ohm |
| Answer» D. Increases to 312.5 ohm | |
| 96. |
Assertion A: Separately excited generators are used in Ward Leonard System of speed control but self-excited are not.Reason R: Self excitation is unsuitable at lower voltage |
| A. | A is correct but R is not a suitable reason for it |
| B. | R is correct but A is not correct |
| C. | A is correct and R is the suitable reason for it |
| D. | A is correct but R is not correct |
| Answer» D. A is correct but R is not correct | |
| 97. |
A shunt generator running at 1000 rpm generated emf of 100 V. If the speed increases to 1200 rpm, the generated emf is |
| A. | 140 V |
| B. | 120 V |
| C. | 240 V |
| D. | 360 V |
| Answer» C. 240 V | |
| 98. |
A torque is developed in an electro mechanical energy conversion device, the value of which depends upon: |
| A. | stator field strength and torque angle |
| B. | stator field and rotor field strengths |
| C. | stator field and rotor field strengths and the torque angle |
| D. | stator field strength only |
| Answer» D. stator field strength only | |
| 99. |
A 4-pole wave-would motor armature has 880 conductors and delivers 120 A. The brushes have been displaced through 3 angular degrees from the geometrical axis. Calculate the additional field current for neutralizing the demagnetisation of the field winding has 1100 turns/pole |
| A. | 0.2 A |
| B. | 0.4 A |
| C. | 2 A |
| D. | 4 A |
| Answer» C. 2 A | |
| 100. |
Compound generators are used to supply power to: |
| A. | incandescent lamps |
| B. | railway circuits |
| C. | elevator motors |
| D. | railway circuits, incandescent lamps and elevator motors |
| Answer» E. | |