In this article, we published the top 200 electrical engineers objective questions and answers for electrical and electronics engineers.
Electrical Engineers Objective Questions
The below list provides all the multiple-choice questions (MCQ) related to electrical engineers.
Answers are available at the bottom of the article.
1. Carbon brushes are used in a dc machine because
| A) | carbon is cheap |
| B) | carbon lubricates and polishes the commutator |
| C) | contact resistance is decreased |
| D) | carbon is abundant |
2. A type of secondary cell that can be recharged but with an electrolyte that cannot be refilled
| A) | Sealed secondary cell |
| B) | Sealed rechargeable cell |
| C) | Alkaline cell |
| D) | Lealanche cell |
3. A stand alone solar power system
| A) | need a full wave rectifier |
| B) | requires the use of dry cells |
| C) | relies on the electric utility at night |
| D) | uses solar panels and batteries |
4. The alternators driven by _____ do not have a tendency to hunt
| A) | diesel engines |
| B) | prime movers |
| C) | steam engines |
| D) | water turbines |
5. Which motor is used to start heavy loads?
| A) | series |
| B) | shunt |
| C) | differentially compounded |
| D) | commulatively compounded |
6. Galvanic cell is the other name of
| A) | secondary cell |
| B) | primary cell |
| C) | voltaic cell |
| D) | solar cell |
7. In a wave winding, the commutator pitch is approximately equal to
| A) | half the pole pitch |
| B) | pole pitch |
| C) | twice the pole pitch |
| D) | thrice the pole pitch |
8. The armature of a dc machine is laminated in order to reduce
| A) | Copper loss |
| B) | Frictional loss |
| C) | Hysteresis loss |
| D) | Eddy current loss |
9. The stator of an alternator is identical to that of a
| A) | 1 phase induction motor |
| B) | dc generator |
| C) | 3 phase induction motor |
| D) | Rosenberg generator |
10. The salient pole construction for field structure of an alternator is generally used for ______ machine
| A) | 4 pole |
| B) | 6 pole |
| C) | 2 pole |
| D) | 8 pole |
11. A transformer operates poorly at very low frequencies because
| A) | primary reactance is too much |
| B) | permeability core is reduced |
| C) | magnetizing current is abnormally high |
| D) | permeability of core is increased |
12. A dc compound generator having full load terminal voltage equal to the no-load generator voltage is called ______ generator
| A) | under compounded |
| B) | flat compounded |
| C) | un compounded |
| D) | over compounded |
13. The demand for a large increase in torque of a dc series motor is met by a
| A) | large decrease in speed |
| B) | large increase in speed |
| C) | large decrease in current |
| D) | small decrease in speed |
14. The open circuit test on a transformer is always made on
| A) | low voltage winding |
| B) | neither low or high voltage |
| C) | either low or high voltage |
| D) | high voltage winding |
15. The greatest percentage of the heat loss in a dc machine is due to
| A) | eddy current loss |
| B) | hysteresis loss |
| C) | copper loss |
| D) | frictional loss |
16. Intermittent sparking at the brushes of dc motor may be caused due to
| A) | an open armature coil |
| B) | incorrect voltage |
| C) | loose coupling |
| D) | intermittent load |
17. In a dc generator armature reaction _______ pole tip
| A) | weakens the flux at the leading |
| B) | strengthens the flux at the leading |
| C) | strengthens the flux at the trailing |
| D) | weakens the flux at the trailing |
18. The size of a dc generator can be reduced by using
| A) | iron commutator |
| B) | magnetic material of high permeability |
| C) | high resistance winding material |
| D) | lap winding |
19. For the same rating, a dc machine has _______ an ac machine
| A) | the same weight as |
| B) | less weight than |
| C) | half the weight than |
| D) | more weight than |
20. In a simplex wave winding, the number of parallel paths is equal to
| A) | 2 |
| B) | 1 |
| C) | number of pair poles |
| D) | number of poles in the machine |
21. A _______ is a group of cells that generates electric energy from their internal chemical reaction
| A) | power supply |
| B) | battery |
| C) | regulator |
| D) | solar energy |
22. Which motor never use belt connected loads?
| A) | Shunt |
| B) | Series |
| C) | Commulatively compounded |
| D) | Differentially compounded |
23. A commutatively compounded motor does not run at dangerous speed at light loads because of the presence of
| A) | series |
| B) | interpoles |
| C) | shunt winding |
| D) | compensating windings |
24. The transformer that should never have the secondary open-circuited when the primary is energized is
| A) | power transformer |
| B) | auto transformer |
| C) | voltage transformer |
| D) | current transformer |
25. A transformer will have zero efficiency at
| A) | no load |
| B) | half full load |
| C) | full load |
| D) | twice the load |
26. The effect of armature reaction is to
| A) | make the flux constant |
| B) | decreased the total flux |
| C) | make the air gap flux uniform |
| D) | increase the total flux |
27. The nature of armature winding of a dc machine is decided by
| A) | number of coils |
| B) | front pitch |
| C) | commutator path |
| D) | back pitch |
28. Four carbon zinc cell in series will provide about
| A) | 8Vdc |
| B) | 2Vdc |
| C) | 9Vdc |
| D) | 6Vdc |
29. The mechanical power developed in a dc motor is maximum when back emf is equal to ______ the applied voltage
| A) | one half |
| B) | twice |
| C) | one fourth |
| D) | one third |
30. To increase current capacity, cells are connected in
| A) | parallel |
| B) | series- parallel |
| C) | series |
| D) | parallel- series |
31. Silver cadmium is secondary cell with a nominal open circuit voltage of
| A) | 1.1V |
| B) | 1.2V |
| C) | 1.35V |
| D) | 1.5V |
32. A 12v battery is rated at 48 ah.
If it must deliver an average of 2.0 a, how long will the battery take before it needs recharging
| A) | 24hrs |
| B) | 48hrs |
| C) | 96hrs |
| D) | 4hrs |
33. For the same rating _______ motor has the least starting torque
| A) | shunt |
| B) | differentially compounded |
| C) | commulatively compounded |
| D) | series |
34. With respect to the direction of rotation, interpoles on a dc motor must have the same polarity as the main poles
| A) | in parallel with them |
| B) | behind them |
| C) | ahead of them |
| D) | beside them |
35. If the lagging load power factor of an alternator is decreased, the demagnetizing effect of the armature reaction
| A) | becomes infinite |
| B) | is decreased |
| C) | remains the same |
| D) | is increased |
36. The ac armature winding of an alternator operates at _______ the field of winding
| A) | much higher voltage than |
| B) | the same voltage as |
| C) | much lesser voltage than |
| D) | half the voltage than |
37. What can be found in a transformer with the open-circuit test?
| A) | Total equivalent resistance |
| B) | Turns ratio |
| C) | Total equivalent leakage resistance |
| D) | Copper losses |
38. What gives the relative activity in forming ion charges for some of the chemical elements?
| A) | Electromotive series |
| B) | Both Electrochemical series & Electromotive series |
| C) | Electrochemical series |
| D) | Electrical series |
39. The brush voltage drop in a dc machine is about
| A) | 10V |
| B) | 20V |
| C) | 0.1V |
| D) | 2V |
40. What is the nominal output of an automotive battery having six lead-acid cells in series?
| A) | 12V |
| B) | 3V |
| C) | 24V |
| D) | 6V |
41. The field structure of a dc machine uses
| A) | Salient pole arrangement |
| B) | Non salient pole arrangement |
| C) | Silicon steel |
| D) | Cast steel |
42. The real working Part of a dc machine is the
| A) | commutator |
| B) | field winding |
| C) | stator |
| D) | armature winding |
43. For given number of poles (2) and armature conductors, a lap winding will carry a wave winding
| A) | more current than |
| B) | less current than |
| C) | half the current than |
| D) | same current as |
44. A separately excited dc generator is not used because
| A) | it is costly |
| B) | a separate dc source is required for field circuit |
| C) | it is bulky |
| D) | voltage drops considerably with load |
45. The efficiency of a transformer will be at maximum when
| A) | copper loss is zero |
| B) | copper loss is equal to constant loss |
| C) | resistance of the two windings are equal |
| D) | leakage reactance of the two windings are equal |
46. A 4 pole dc machine has magnetic circuits
| A) | 2 |
| B) | 8 |
| C) | 4 |
| D) | 6 |
47. The speed at which a 6 pole alternator should be drive to generate 50 cycles per second is
| A) | 1200 rpm |
| B) | 500 rpm |
| C) | 1000 rpm |
| D) | 1500 rpm |
48. The terminal voltage of a ________ generator vary widely with changes in load current
| A) | shunt |
| B) | over compounded |
| C) | series |
| D) | flat compounded |
49. An ideal transformer is one which
| A) | has the same number of primary and secondary turns |
| B) | has the same primary and secondary voltage |
| C) | has no losses and leakage reactance |
| D) | does not work |
50. The maximum flux produced in the core of a transformer is
| A) | inversely proportional to primary voltage |
| B) | inversely proportional to supply frequency |
| C) | inversely proportional to secondary voltage |
| D) | directly proportional to supply frequency |
51. When load is removed, the motor that will run at the highest speed is the ______ motor
| A) | shunt |
| B) | differentially compounded |
| C) | series |
| D) | commulatively compounded |
52. The rotor of a turbo alternator is made cylindrical in order to reduce
| A) | wind age loss |
| B) | eddy current loss |
| C) | copper loss |
| D) | hysteresis loss |
53. The voltage regulation of an alternator with a power factor of 0.8 lagging is ______ at unity power factor
| A) | greater than |
| B) | D. 100% |
| C) | the same as |
| D) | smaller than |
54. Machine in which torque is produced by the interaction of ac current in the stator and dc currents in the rotor turning synchronism
| A) | synchronous motor |
| B) | induction motor |
| C) | squirrel cage motor |
| D) | stepper motor |
55. the load on an alternator is increased, the terminal voltage increases if the load power factor is
| A) | lagging |
| B) | leading |
| C) | unity |
| D) | zero |
56. The most commonly used method of speed control of a dc motor is by varying
| A) | voltage applied to the motor |
| B) | armature circuit resistance |
| C) | felids strength |
| D) | effective number of conductors in series |
57. The greatest eddy current loss occurs in the ______ of a dc machine
| A) | field poles |
| B) | armature |
| C) | yoke |
| D) | commutating process |
58. A dc motor is still used in industrial applications because it
| A) | provides fine speed control |
| B) | is cheap |
| C) | has no replacement |
| D) | is simple in construction |
59. The air gap in an alternator is ______ in an induction machine
| A) | much longer than |
| B) | about the same as |
| C) | much shorter than |
| D) | one-half than |
60. DC series motors are used in those applications where ______ required
| A) | variable speed |
| B) | constant speed |
| C) | low no load speed |
| D) | high starting torque |
61. Which of the following is not a secondary cell?
| A) | Silver-oxide |
| B) | Silver-zinc |
| C) | Lead-acid |
| D) | Nickel-iron |
62. A storage battery in which the electrodes are grids of lead containing lead oxides that changes in composition during charging and discharging and the electrolyte is dilute sulfuric acid
| A) | Leclanche battery |
| B) | Faure storage battery |
| C) | Nickel cadmium battery |
| D) | Lead and battery |
63. When the speed of a dc motor increases, its armature current
| A) | increases |
| B) | remains the same |
| C) | becomes infinite |
| D) | decreases |
64. The core type transformer is generally suitable for
| A) | low voltage and high output |
| B) | low voltage and low output |
| C) | high voltage and high output |
| D) | high voltage and small output |
65. Majority of alternators in use have
| A) | revolving field type construction |
| B) | stationary field type construction |
| C) | revolving ac armature winding |
| D) | stationary ac armature winding |
66. For the same rating _____ motor has the highest staring torque
| A) | series |
| B) | differentially compounded |
| C) | shunt |
| D) | commutatively compound |
67. The ac armature winding of an alternator is
| A) | pi connected |
| B) | star delta connected |
| C) | generally delta connected |
| D) | always star connected |
68. Cumulatively compounded motors are used in applications where ______ is required
| A) | sudden heavy loads for a short duration |
| B) | constant speed |
| C) | poor speed regulation |
| D) | variable speed |
69. When the secondary of a transformer is short-circuited, the primary inductance
| A) | is increased |
| B) | remains the same |
| C) | is decreased |
| D) | becomes zero |
70. Armature reaction in a dc motor is increased
| A) | when the armature current decreases |
| B) | when the field current increases |
| C) | by interpole |
| D) | When the armature current increases |
71. Which of the following is not a primary cell?
| A) | Mercuric oxide |
| B) | Edison call |
| C) | Carbon-zinc |
| D) | Zinc-chloride |
72. The rating of an alternator is expressed in
| A) | KVAR |
| B) | kVA |
| C) | kW |
| D) | HP |
73. What is the approximate efficiency of large transformer?
| A) | 95% |
| B) | 65% |
| C) | 80% |
| D) | 50% |
74. The core type transformer provides
| A) | much longer magnetic pattern |
| B) | lesser average length per turn |
| C) | longer magnetic path |
| D) | shorter magnetic path |
75. Volt is a unit of
| A) | magneto motive force |
| B) | energy |
| C) | electromotive force |
| D) | force |
76. DC machines which are subjected to abrupt changes of load are provided with
| A) | interpole windings |
| B) | copper brushes |
| C) | equalizers |
| D) | compensating winding |
77. In a very large dc motor with severe heavy duty, armature reaction effects are corrected by
| A) | fixing the brush position |
| B) | shifting the brush position |
| C) | using compensatory windings in addition to interpoles |
| D) | using interpole only |
78. The shaft torque in a dc motor is less than total armature torque because of ______ in the motor
| A) | iron and friction losses |
| B) | hysteresis loss |
| C) | field losses |
| D) | copper losses |
79. A transformer will work on
| A) | dc only |
| B) | pulsating dc |
| C) | ac only |
| D) | ac as well as dc |
80. The voltage of the bus bar to which several alternators are paralleled may be raised by simultaneously _______ of all alternators
| A) | decreasing field excitation |
| B) | increasing input to prime movers |
| C) | decreasing input to prime movers |
| D) | increasing field excitation |
81. the primary leakage flux links
| A) | secondary winding only |
| B) | primary winding only |
| C) | neither primary nor secondary windings |
| D) | both primary and secondary windings |
82. An 8 pole duplex lap winding will have ______ parallel paths
| A) | 8 |
| B) | 32 |
| C) | 16 |
| D) | 4 |
83. If the excitation of an alternator operating in parallel with other alternators is decreased, its
| A) | power factor becomes more leading |
| B) | power factor becomes unity |
| C) | output kW will change |
| D) | power factor becomes more lagging |
84. The armature winding of a dc Machine is ______ winding
| A) | a closed circuit |
| B) | partly open circuit and partly closed circuit |
| C) | an open circuit |
| D) | lap |
85. A graphical relation between the generated emf and the field current of a machine
| A) | voltage generation curve |
| B) | voltage current curve |
| C) | magnetization curve |
| D) | current generation curve |
86. In a lap winding, the number of the brushes required is equal to
| A) | number of coils |
| B) | number of poles |
| C) | commutator pitch |
| D) | number of pairs of poles |
87. In an auto transformer, the primary and secondary are _______ coupled
| A) | only electrically |
| B) | only magnetically |
| C) | directly |
| D) | magnetically as well as electrically |
88. considered as the main types of battery
| A) | Voltaic cell and lithium cell |
| B) | Lithium cell and alkaline |
| C) | Leclanche cell and carbon zinc |
| D) | Carbon-zinc dry cell and lead sulphuric wet cell |
89. The common dry cell, which is a primary cell having a carbon positive electrode and a zinc negative electrode in an electrolyte of sal ammoniac and a depolarizer
| A) | Lithium cell |
| B) | Lead acid cell |
| C) | Faure storage cell |
| D) | Leclanche cell |
90. An example of rechargeable dc source is an/a
| A) | optoisolator |
| B) | photovoltaic cell |
| C) | lithium battery |
| D) | lead acid battery |
91. The armature winding of a dc machine is placed on the rotor to
| A) | reduce losses |
| B) | save iron |
| C) | facilitate commutation |
| D) | reduce armature reaction |
92. Which is the most suitable for punch presses?
| A) | differentially compounded motor |
| B) | commutatively compounded motor |
| C) | series motor |
| D) | shunt motor |
93. low speed alternators are driven by
| A) | hydraulic turbines |
| B) | steam engines |
| C) | diesel engines |
| D) | steam turbines |
94. Damper windings are used in alternators to
| A) | reduce eddy current loss |
| B) | reduce wind age losses |
| C) | prevent hunting |
| D) | achieve synchronism |
95. The effect of leakage flux in a transformer is to
| A) | increase copper losses |
| B) | decrease copper losses |
| C) | reduce eddy current losses |
| D) | cause voltage drop in the windings |
96. If the excitation of an alternator operating in parallel with other alternators is increased above the normal value excitation of excitation its
| A) | output current decreases |
| B) | power factor becomes more leading |
| C) | output kw decreases |
| D) | power factor becomes more lagging |
97. A dc series motor is most suitable for
| A) | lathes |
| B) | cranes |
| C) | pump |
| D) | punch presses |
98. In a practical transformer, copper losses account for how many percent of the total losses?
| A) | 75% |
| B) | 95% |
| C) | 85% |
| D) | 25% |
99. A triplex wave winding will have ______ parallel paths
| A) | 8 |
| B) | 4 |
| C) | 6 |
| D) | 2 |
100. What is the output of a lead acid cell?
| A) | 1.5V |
| B) | 1.35V |
| C) | 2.1V |
| D) | 1.25V |
101. The winding of the transformer with greater number of turns will be
| A) | high voltage winding |
| B) | either high or low voltage winding |
| C) | high power |
| D) | low voltage winding |
102. Excessive sparking at the brushes may caused due to
| A) | dirt on the commutator |
| B) | misalignment of machine |
| C) | loose coupling |
| D) | worn bearings |
103. The demand for a large increase in torque of a dc shunt motor is met by a
| A) | large increased in speed |
| B) | small increased in current |
| C) | large decreased in speed |
| D) | large increased in current |
104. In the short circuit test in a transformer, _______ winding is generally short circuited
| A) | low voltage |
| B) | either low or high voltage |
| C) | high voltage |
| D) | neither low nor high voltage |
105. The voltage per turn of the primary of a transformer is _______ the voltage per turn of the secondary
| A) | more than |
| B) | the same as |
| C) | less than |
| D) | twice |
106. The number of cycles generated in a 6 pole alternator in one revolution is
| A) | 2 |
| B) | 5 |
| C) | 3 |
| D) | 6 |
107. The iron losses in a dc motor depend upon
| A) | both flux and speed |
| B) | flux only |
| C) | speed only |
| D) | temperature |
108. To produce an output of 7.5v, how many carbon zinc cells are connected in series?
| A) | 4 |
| B) | 6 |
| C) | 5 |
| D) | 3 |
109. Which of the following is the main function of a dc motor?
| A) | to change mechanical energy to electrical energy |
| B) | to generate power |
| C) | to change electrical energy to mechanical energy |
| D) | to change chemical energy to mechanical energy |
110. Hot bearings of a dc motor may be caused by
| A) | incorrect voltage |
| B) | poor ventilation |
| C) | lack of dirty lubricant |
| D) | loose coupling |
111. A machine with field excitation by both shunt and series windings
| A) | complex machine |
| B) | universal machine |
| C) | shunt/ series machine |
| D) | compound machine |
112. For a given dc generator, the generated voltage depends upon
| A) | both speed and flux |
| B) | armature rotation |
| C) | speed only |
| D) | flux only |
113. For the same rating, the size of low speed alternator is ______ that of high speed alternator
| A) | about the same as |
| B) | more than |
| C) | twice |
| D) | less than |
114. Three cells connected in series from a
| A) | voltage divider |
| B) | voltage multiplier |
| C) | hybrid |
| D) | battery |
115. The friction and wind age losses in a dc motor depends upon
| A) | flux |
| B) | field and armature resistance |
| C) | speed |
| D) | armature current |
116. The frequency of emf generated in an 8 pole alternator at 900 rpm is
| A) | 120hz |
| B) | 60hz |
| C) | 50hz |
| D) | 240hz |
117. The voltage output of a cell depends on
| A) | electrochemical series |
| B) | electromotive series |
| C) | its elements |
| D) | its electrodes |
118. What refers to a method in which the charger and the battery are always connected to each other for supplying current to the load
| A) | Continuous charging |
| B) | Infinite charging |
| C) | On line charging |
| D) | Float charging |
119. Excessive motor vibration is caused by
| A) | too much brush tension |
| B) | bent shaft |
| C) | open armature coil |
| D) | worn bearings |
120. In a dc machine, the number of commutator segments is equal to
| A) | number of conductors |
| B) | twice the number of coils |
| C) | twice the number of poles |
| D) | number of coils |
121. Combination of ac motor, dc generator, and exciter to provide adjustable voltage dc power to a dc motor.
| A) | Universal motor |
| B) | Ward-Leonard system |
| C) | Compound motor |
| D) | Half wave SCR adjustable voltage supply |
122. The torque developed by a dc motor is directly proportional to
| A) | flux per pole x applied voltage |
| B) | flux per pole x armature current |
| C) | armature resistance x armature current |
| D) | armature resistance x applied voltage |
123. The armature of a dc machine is made of
| A) | silicon steel |
| B) | cast steel |
| C) | soft iron |
| D) | wrought iron |
124. In a chemical cell current is the movement of
| A) | positive ions only |
| B) | negative ions only |
| C) | positive and negative ions |
| D) | positive charges |
125. The speed of a dc motor is
| A) | inversely proportional to armature current |
| B) | inversely proportional to flux per pole |
| C) | inversely proportional to applied voltage |
| D) | directly proportional to flux per pole |
126. A motor takes a large current at starting because
| A) | back emf is high |
| B) | shunt field is producing weak field |
| C) | back emf is low |
| D) | the armature resistance is high |
127. The amount of copper in the primary is ______ that of the secondary
| A) | about the same as |
| B) | twice |
| C) | smaller than |
| D) | greater than |
128. Which is a variable speed motor?
| A) | differentially compounded |
| B) | series |
| C) | commutatively compounded |
| D) | shunt |
129. High speed alternators are driven by
| A) | hydraulic turbines |
| B) | diesel engine |
| C) | steam turbines |
| D) | diesel engine |
130. The greatest percentage of power loss in a dc motor is due to
| A) | friction loss |
| B) | wind age loss |
| C) | core loss |
| D) | copper loss |
131. The common 9v flat battery for transistor radio has ______ cells connected ins series
| A) | 12 |
| B) | 9 |
| C) | 3 |
| D) | 6 |
132. A storage battery in which the plates consist if lead antimony supporting grids covered with a lead oxide paste immersed in weak sulfuric acid
| A) | Leclanche cell |
| B) | primary battery |
| C) | secondary battery |
| D) | Faure storage battery |
133. The stator of n alternator is wound for ______ on the rotor
| A) | twice the number of poles |
| B) | the same number of poles as |
| C) | less number of poles than |
| D) | a more number of poles than |
134. Small Dc machines generally have ______ poles
| A) | 6 |
| B) | 4 |
| C) | 8 |
| D) | 2 |
135. As the load increases a, ______ motor will speed uo
| A) | differentially compounded |
| B) | shunt |
| C) | series |
| D) | commutatively compounded |
136. What cell is used to detect infrared radiation, either its generated voltage or its change of résistance may be used as a measure of the intensity of the radiation?
| A) | Faure storage cell |
| B) | Leclanche cell |
| C) | lead sulfide cell |
| D) | infrared cell |
137. The efficiency of the turbo-alternator ______ with increase in speed
| A) | becomes 100% |
| B) | decreases |
| C) | increases |
| D) | remains the same |
138. The deciding factor in the selection of a dc motor for a particular application is its characteristics
| A) | speed armature current |
| B) | speed torque |
| C) | speed |
| D) | torque armature current |
139. This synchronous reactance of an alternator is generally ______ armature resistance
| A) | 10 times smaller than |
| B) | 10 – 100 times greater than |
| C) | 5 times smaller than |
| D) | 5 times greater than |
140. For 20% increase in current, the motor that will give the greatest increase in torque is ______ motor
| A) | shunt |
| B) | series |
| C) | commulatively compounded |
| D) | differentially compounded |
141. The field winding of an armature is _____ excited
| A) | dc |
| B) | battery |
| C) | ac |
| D) | both ac and dc |
142. To increase the voltage output, cells are connected in
| A) | parallel |
| B) | series-parallel |
| C) | series |
| D) | parallel-series |
143. The current in armature conductors of a dc machine is
| A) | pure dc plus pulsating dc |
| B) | pure dc |
| C) | pulsating dc |
| D) | ac |
144. In a dc motor, the brushes are shifted from the mechanical neutral plane in a direction opposite to the rotation to
| A) | produce flat characteristics |
| B) | reduced sparking |
| C) | decreased speed |
| D) | increase speed |
145. The flux in the core o a single phase transformer is
| A) | partly alternating and partly rotating |
| B) | constant |
| C) | purely alternating one |
| D) | purely rotating one |
146. The amount of back emf of shunt motor will increase when
| A) | the field is weakened |
| B) | the load is decreased |
| C) | the load is increased |
| D) | the field is strengthen |
147. A galvanic cell resulting from difference in potential between adjacent on the surface of a metal immersed in an electrolyte
| A) | local cell |
| B) | lithium cell |
| C) | NiCd cell |
| D) | lead acid cell |
148. The running speed of a dc series motor is basically determined by
| A) | field excitation |
| B) | armature resistance |
| C) | applied voltage |
| D) | load |
149. The distribution of load between two alternators operating in parallel can be changed by changing
| A) | phase sequence |
| B) | driving torques of prime movers |
| C) | current direction |
| D) | field excitation of alternators |
150. Two things which are same for primary and secondary of transformer are
| A) | ampere turns and voltage per turn |
| B) | number of turns and power |
| C) | current and inducted voltage |
| D) | resistance and leakage reactance |
151. Leclanche cell is the other name of
| A) | carbon zinc cell |
| B) | lead acid cell |
| C) | zinc chloride |
| D) | mercuric cell |
152. The back emf or counter emf in a dc motor
| A) | opposes the applied voltage |
| B) | opposes the armature current |
| C) | aids the supplied voltage |
| D) | aids the armature current |
153. If a power transformer is operated at very high frequencies then
| A) | core losses will be excessive |
| B) | core loss is negligible |
| C) | primary reactance is too much increased |
| D) | primary will draw large power |
154. A transformer is an efficient device because it
| A) | uses electric coupling |
| B) | is a static device |
| C) | uses capacitive coupling |
| D) | uses inductive coupling |
155. The yoke of a dc machine carries ______ poke flux
| A) | one fourth of |
| B) | one third of |
| C) | two times of |
| D) | one half of |
156. The open circuit test on a transformer gives
| A) | friction losses |
| B) | copper losses |
| C) | total losses |
| D) | iron losses |
157. Nickel-iron cells is a secondary cell with a nominal open- circuit voltage output of 1.2 and is otherwise known as
| A) | Galvanic cell |
| B) | Voltaic cell |
| C) | Leclanche cell |
| D) | Edison cell |
158. The disadvantage of a short pitched coil is that
| A) | voltage round coil is increases |
| B) | waveform becomes non-sinusoidal |
| C) | voltage round the coil is reduced |
| D) | harmonics are introduced |
159. A method of converting chemical energy into electric energy by dissolving two different conducting materials in an electrolyte
| A) | Battery |
| B) | Cell |
| C) | Charging |
| D) | Voltaic cell |
160. Which of the following is the main function of a battery?
| A) | To provide a source of variable dc voltage of variable polarity |
| B) | To provide a source of steady DC voltage to fixed polarity |
| C) | To provide a source of variable dc voltage of fixed polarity |
| D) | To provide a source of steady dc voltage of variable polarity |
161. Why are the field poles and the armature of a dc machine laminated?
| A) | to reduce armature reaction |
| B) | to decrease the speed |
| C) | to reduce eddy current |
| D) | to reduce the weight of the machine |
162. A series motor will over speed when
| A) | load is removed |
| B) | the load is increased |
| C) | the field id opened |
| D) | the armature circuit is open |
163. In a vacuum cleaner, _____ motor is generally used
| A) | series |
| B) | commutatively compounded |
| C) | shunt |
| D) | differentially compounded |
164. DC shunt motors are used in those applications where ______ is required
| A) | practically constant speed |
| B) | variable speed |
| C) | high starting torque |
| D) | high no load speed |
165. Transformers having ratings less than 5kva are generally
| A) | self cooled |
| B) | oil cooled |
| C) | water cooled |
| D) | natural air cooled |
166. If a transformer core has air gaps then
| A) | hysteresis loss is decreased |
| B) | magnetizing current is greatly increased |
| C) | reluctance of magnetic path is decreased |
| D) | eddy current is increased |
167. The speed of a _______ motor is practically constant
| A) | commutatively compounded |
| B) | series |
| C) | shunt |
| D) | differentially compounded |
168. The commutator pitch for a simplex lap winding is equal to
| A) | poles pairs |
| B) | 1 |
| C) | number of poles of the machines |
| D) | 2 |
169. Back emf in a dc motor is maximum at
| A) | half full load |
| B) | full load |
| C) | no load |
| D) | three fourth full load |
170. The voltage regulation of an alternator is larger than of a dc generator because of
| A) | large leakage reactance |
| B) | complex effects of armature reaction |
| C) | large armature resistance |
| D) | small armature resistance |
171. In an alternator, the effect of armature reaction is minimum at power factor of
| A) | 0.866 leading |
| B) | 0.866 lagging |
| C) | 0.5 lagging |
| D) | Unity |
172. High voltage dc machines use what winding?
| A) | open circuit |
| B) | Lap |
| C) | either lap or wave |
| D) | wave |
173. The coupling field between electrical and the mechanical systems of a dc machine is
| A) | electromagnetic field |
| B) | electric field |
| C) | magnetic field |
| D) | both electric and magnetic fields |
174. The yoke of a dc machine is made of
| A) | silicon steel |
| B) | aluminium |
| C) | cast steel |
| D) | soft iron |
175. The main drawback of a dc shunt generator is that
| A) | terminal voltage drops considerably with load |
| B) | it is expensive |
| C) | generated voltage is small |
| D) | shunt field circuit has high resistance |
176. Which DC machines are the most common?
| A) | 8 pole |
| B) | 2 pole |
| C) | 6 pole |
| D) | 4 pole |
177. Which of the following is a dry storage cell?
| A) | Edison cell |
| B) | Nickel cadmium cell |
| C) | Mercury cell |
| D) | Leclanche cell |
178. The number of parallel paths in a simplex lap winding is equal to
| A) | 1 |
| B) | number of poles |
| C) | 2 |
| D) | number of pair poles |
179. In case if a 4 pole machine, 1 mechanical degree corresponds to ______ electrical degree
| A) | 4 |
| B) | 6 |
| C) | 2 |
| D) | 8 |
180. The synchronous reactance of an alternator ______ as the iron is saturated
| A) | becomes doubled |
| B) | remains the same |
| C) | increases |
| D) | decreases |
181. A small 9V battery might be used to provide power to
| A) | a radio transmitter |
| B) | an electric stove |
| C) | an electronic calculator |
| D) | a personal computer |
182. When the load on a transformer is increased, the eddy current loss
| A) | remains the same |
| B) | is increased |
| C) | is decreased |
| D) | becomes zero |
183. A series motor designed to operate on dc or ac
| A) | Compound motor |
| B) | Series motor |
| C) | Shunt motor |
| D) | Universal motor |
184. By laminating the core of a transformer, _______ decreases
| A) | copper loss |
| B) | eddy current loss |
| C) | hysteresis loss |
| D) | leakage reactance |
185. AC machine in which the torque is produced by the interaction of currents in the stator and currents induced in the motor by transformer action
| A) | induction motor |
| B) | synchronous motor |
| C) | stepper motor |
| D) | squirrel cage motor |
186. Connecting batteries of equal voltage in parallel
| A) | increases the internal resistance |
| B) | multiplies the voltage available |
| C) | multiplies the current available |
| D) | reduces the power available |
187. Which of the most suitable motor for elevator
| A) | Commutatively compounded |
| B) | Differentially compounded |
| C) | Series |
| D) | Shunt |
188. Overheating of a dc motor is often due to
| A) | insufficient end play |
| B) | overloads |
| C) | loose parts |
| D) | rough commutator |
189. The field winding of a dc shunt machine usually carries _____ of the rated current of the machine
| A) | 15% to 20% |
| B) | less than 0.5% |
| C) | 2% to 5% |
| D) | more than 20% |
190. After a shunt motor is up to speed the speed may ne increased considerably by
| A) | reducing the load |
| B) | decreasing field circuit resistance |
| C) | increasing field circuit resistance |
| D) | increasing the armature circuit resistance |
191. Which motor has the best speed regulation?
| A) | Series |
| B) | Shunt |
| C) | Differentially compounded |
| D) | Commutatively compounded |
192. The frequency of the system with which several alternators are parallel can be increased by simultaneously ______ of all generators
| A) | decreasing the speed of prime movers |
| B) | increasing the speed of prime movers |
| C) | decreasing the field excitation |
| D) | increasing the field excitation |
193. a constant voltage source has
| A) | High internal resistance |
| B) | low internal resistance |
| C) | minimum efficiency |
| D) | minimum current capacity |
194. The synchronous reactance of an alternator is due to
| A) | leakage flux |
| B) | armature reaction |
| C) | dc field excitation |
| D) | hysteresis loss |
195. Difference between the speed of a rotating magnetic field and the associated rotor
| A) | slip |
| B) | salient pole |
| C) | pull out torque |
| D) | split |
196. Why are carbon brushes preferable compared to copper brushes
| A) | they reduce sparking |
| B) | they have lower resistance |
| C) | they have longer life |
| D) | they are cheaper |
197. A transformer is so designed that primary and secondary windings have
| A) | loose magnetic coupling |
| B) | tight magnetic coupling |
| C) | good electric coupling |
| D) | critical magnetic coupling |
198. When the primary of a transformer is connected to a dc supply
| A) | core losses are increased |
| B) | a primary draw small current |
| C) | primary may burned out |
| D) | primary leakage reactance is increased |
199. The temperature rise of a transformer is directly proportional to
| A) | leakage reactance |
| B) | apparent power |
| C) | reactive power |
| D) | true power |
200. One of the following is a false statement
| A) | primary cell is not rechargeable |
| B) | storage cell has a reversible chemical reaction |
| C) | lead acid cell is rechargeable |
| D) | carbon zinc cell has unlimited shelf life |
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