QUESTION BANK : ELECTRICAL FUNDAMENTALS
Electron Theory
1. Pressure is used to produce voltage, this is
1. piezo electric effect 2. thermal electric effect 3. static electric 4. all
2. Materials have more than half of valence electrons (Eismin, Pg – 2)
1. conductors 2. insulators 3. semi-conductors
3. Element can be divided by (Eismin,Pg – 2)
1. hammering 2. nuclear disintegration
3. heating 4. all
4. If we increase the dis of two charged bodies from 2 millimeters to 5 meters force between them 1. 6.25 x 106 times less
2. 6.25 x 106 times more
3. coulomb law will not act
4. same
5. Substances composed of only one type of atom are called (FA-9A/267)
1. Molecule 2. elements 3. Compound 4. none
6. Hydrogen, oxygen, copper are the (FA-9A/267)
1. compounds 2. elements 3. only gases 4. all
7. Electrical conductivity of a metal is due to – (Grob-19/20)
1. free electrons 2. free protons 3. holes 4. ions
8. In practice earth is choosen as a place of zero electric potential because it :- (SOURCE-INTERNET) 1. Is non conducting
2. Is easily available
3. Keeps loosing or gaining electric charges every day
4. Has almost constant zero potential
9. Pure metals generally have - BLT
1. high conductivity and positive temperature coefficient
2. high conductivity and large temperature coefficient 3. low conductivity and zero temperature coefficient 4. low conductivity and high temperature coefficient.
Static Electricity and Conduction
10. Unit of conductance is
1. Mho
2. Kappa
-13.
Ohm
4.
all
11. Static electricity can be generated by: (9A,
P-269)
1. friction 2. contact 3. induction 4. all the above
12. One Coulomb charge contains (Grob/24/25)
1. 6.25 x 1019 electrons 2. 6.25 x 1018 electrons 3. 6.25 x 1017 electrons 4. 6.25 x 1021 electrons
1. electromotive 2. electrostatic 3. magneto motive 4. centripetal
14. If three coulombs of electricity flow through a conductor in three seconds the current is (Grob/31)
1. one ampere 2. one half ampere 3. six ampere 4. one third ampere 15. Ampere /second could be the unit of – (BLT)
1. e.m.f. 2. charge 3. power 4. energy
16. Field of force existing around a charged body is: (9A, P-269)
1. electrostatic field 2. electro magnetic field 3. atomic field 4. none of the above 17. First law of electro statics state that -
1. Like charges repel each other 2. Like charges attract each other 3. Unlike charges attract each other
4. Both 1 and 3 are correct
18. Second law of electrostatic deal with - (B.L Thereja – 190) 1. Charge
2. Force
3. Distance between two charge body
4 all of the above
DC Sources of
Electricity-19. Red lead paste is done in (Eismin, Pg – 36)
1. anode 2. cathode 3. both 4. only on anode
20.Expander which is used in Lead acid cell is (Eismin, Pg – 36)
1. Graphite 2. Ground carbon 3. Lampblack 4. All are correct
21. 4 cells of 2.0,15 amp – hr, 2 are in series and 2 are in parallel, Now this arrangement is connected in series, output battery would be of
1. 6 v 30 A A-H 2. 4 v 15 A-H 3. 6 v 15 A-H 4. no battery can be formed
22. Sealed type battery is also known as (Eismin, Pg-30)
1. Re-combinant gas type 2. Re-calibrated gas type 3. Re-continued gas type 4. all
23. Oxygen gas is exerted at (Eismin , Pg – 47)
1. anode 2. cathode 3. both (a) and (b) 4. no oxygen 24. NiOOH remains at positive plate of Ni-cd (Eismin, Pg – 49)
1. charged condition 2. during discharged condition 3. no Ni oxyhydroxide forms 4. all are correct
25. all are correct
14. The output voltage of a lead-acid cell is about: (BLT Electronics, P-84.
1. 1.5 2. 2.2 3. 1.25 4. 6
26. During removal of battery from the a/c ____ terminal is disconnected at last in order to avoid ______ short
Eismin/53.
1. negative, accidental 2. positive, accidental
27. When cell is loaded, the terminal voltage (Grob/347)
1. is less then emf of cell by ‘I r’ drop 2. is equal to cell’s emf 3. is greater than emf by ‘I r’ drop 4. all of the above are correct 28. Sulphation in cell means (9A/309)
1. to charge the cell at slow rate 2. to discharge it at slow rate
3. sulphate layer of active material becomes hard and useless
4. boiling of electrolyte
29. Factors affecting the capacity of cell are (9A/311.
1. rate of discharge or recharge 2. no of plates area of plates 3. density of electrolyte and active material mass 4. all of the above
30. Ni / Cad cell is advantageous over Pb-acid cell from _____ point of view (9A/313. 1. low maintenance cost and long service life 2. short recharge time and good reliability 3. excellent reliability and good starting ability 4. all of the above
31. In case of discharge of lead acid battery (Grob/354.
1. formation of PbSO4 on both plates occurs 2. specific gravity of electrolyte increases 3. cell emf. Increases
4. colour of positive plates becomes chocolate deep brown.
32. The negative terminal of a battery means it has ---- (Grob, 3A6)
1. excess of electrons. 2. excess of protons 3. deficiency of electrons 4. all of the above 33. ____ is one of the factor of thermal run away of Nickel/Cadmium cell(Eismin/47)
1. damaged layer of cellophane material 2. exothermic reactions at electrodes plates 3. 30% of dilute KOH by volume 4. both 1 & 2
34. The current delivering capacity of a cell depends on: (9A) 1. condition of the electrolyte 2. specific gravity of electrolyte
3. physical size of electrode 4. all the above
35. Which of the following is a dry but rechargeable cell: Electronics, P-84.
1. nickel-cadmium cell 2. mercury cell
3. lead-acid cell 4. solar cell
36. Rating of a battery is usually expressed in: (BLT Electronics, P-84. 1. watt-hour 2. joule 3. ampere-hour 4. amperes
37 Which method is used to rapidly charge the battery: (Eismin-P-42. 1. Constant current and varying voltage method
2. Varying voltage and varying current method
3. Constant voltage and varying current method
4. none
38. Vicious cycle occurs in: (Eismin-P-47)
1. Generator 2. Battery 3. Motor 4. Transformer
39 Sulphation in lead acid battery occurs due to: (BLT1991-P-361.
1. Trickle charging 2. Heavy discharging 3. Incomplete charging 4. Fast charging
40 Vicious cycle is another name of: (Eismin-P-47)
1. Heavy discharge cycle 2. Thermal runaway
41. Porous separators are used in a lead acid battery to: (9A,P-308)
1. keep +ve & -ve plates from touching & shorting each other
2. to allow electrolyte to circulate freely around plates 3. safeguard +ve plate from distortion
4. all the above
42. Construction of vertical ribs on separators permits: (9A,P-308) 1. free circulation of electrolyte around plates
2. provides a path for sediment to settle to the bottom of cell
3. both (a) and (b)
4. none of the above
43. Storage battery can be charged with: (9A,P-313.
1. constant voltage 2. constant current 3. constant frequency 4. both (1) and (2) 44. In case Ni-cad electrolyte spills on body parts, should be rinsed with: (9A,P-314.
1. vinegar 2. lemon juice 3. boric acid solution 4. all the above
45. Ni-Cd is preferred to lead acid battery as it has: (Ref. FAA 9A, Pg. 313. 1. Short recharge time 2. Excellent reliability
3. Good starting capability 4. All
46. In lead acid battery (discharged state) negative plate used is: (Ref. FAA 9A, Pg. 313.
1. Pb02 2. Pb SO4 3. Ni (OH) 2 4. Cd (OH) 2
47. In case of Ni/Cd battery, during discharge _____ remains unchanged (Eismin/47) 1. voltage of cell 2. specific gravity
3. amount of active material at cathodes 4. amount of active material at positive plate
48. During the installation of battery in a/c, ___ terminal is connected first and in order to ___ (Eismin, 53. 1. positive, complete the circuit 2. negative, complete the circuit
3. positive, avoid the accidental short 4. negative, avoid the accidental short
49. The capacity of a lead acid cell depends on (9A/310) 1. temperature 2. quantity of active material 3. rate of discharge 4. all of the above
50 Nickel-cadmium batteries which are stored for a long period of time will show a low liquid level because (9A/314, Eismin -50)
1. Electrolyte evaporates through the vents 2. of current package form individual cells
3. Electrolyte becomes absorbed into the plates
4. None of these
51. What may result if water is added to nickel cadmium battery when it is not fully charged ? (9A/314, Eismin – 40) 1. Excessive electrolyte deletion
2. Excessive spillage is likely to occur during the charging cycle
3. No adverse effects since water may be added any time 4. None of these
52. In a constant current charging system, a battery requires attention at the end of charge to avoid (9A/312, Eismin – 42.
1. Sulphation of battery 2. Spilling of electrolyte 3. Evaporation of electrolyte 4. Danger of overheating
53. Active elements in a lead acid battery - (Eismin /35) 1. nickel hydrate and iron oxide 2. lead peroxide and spongy lead
3. manganese dioxide and carbon 4. spongy lead
54. Electrolyte used in lead acid battery is (Eismin /35)
1. dilute sulphuric acid 2. caustic potash 3. nitric acid 4. none 55. When the temperature is increased, specific gravity of electrolyte (Eismin /41.
1. increases 2. decreases 3. remains same 4. none
56. The capacity of a battery is expressed in (Eismin /44.
1. ampere hour 2. ampere volt 3. percentage 4. volts
57. While testing the specific gravity of the electrolyte of a nickel cadmium battery, it shows a reading of 1.300,
that means (9A /31A)
1. the battery is fully charged 2. the battery is moderately charged 3. the battery has lesser charge 4. the charging state can't be predicted
58. Hydrogen will be released at __ plates and oxygen will be released at ____ plates of a Ni-Cd battery (Eismin/49)
1. negative, positive
2. negative at charging & positive at discharging 3. positive, negative
4. positive at discharging) & negative at charging)
59. When a battery is connected to a charger, which way should the connection be made: (Dale Crane, P-23.
1. positive of the charger to the positive of the battery
2. positive of the charger to the negative of the battery 3. it really does not make any difference
4. none of the above
60. What characteristics of a lead acid battery determines its ampere hour capacity: (Dale Crane, P-23. 1. the numbers of cells in the battery 2. the area of the plates
3. the density of electrolyte 4. the internal resistance of the battery
61. How can you tell when a battery on constant current charge is fully charged: (Dale Crane, P-23. 1. the specific gravity doesn’t show any increase in three consecutive readings taken one hour apart
2. all of the cell are gassing freely
3. both of the above conditions
4. the battery voltage stops rising
62. The state of charge of Ni-Cd battery can be found out by :- (CAIP-2- P-11.7) 1. Open circuit voltage 2. Amount of gassing
3. Measured discharge test 4. Specific gravity
63. Ni-cd battery when connected for charging the gassing indicates: (Pallet-P-23. 1. Battery is receiving proper charge and should continue charging
2. End of charge and beginning of overcharging
3. Beginning of charge and should be charged at the rate prescribed 4. None of the these
64. Two primary cells of 12 V and capacity 60 AH connected in parallel: (Grob-P-360) 1. V= 24V. cap 60 AH 2. V= 12V. cap 60 AH 3. V= 12V. cap 120 AH
1. Baking soda 2. Water dilute Solution of boric acid
3. Plenty of water 4. Soda bi carbonate
66. Negative plate of a ni-cd battery is made of: (Eismin-P-49)
1. Metallic cd 2. Cd hydroxide 3. Ni hydroxide 4. Nickel
67. MTCS regarding mixing of the electrolyte for lead acid battery: (Dale Crane, P-51.
1. the electrolyte that is furnished with a dry charged battery must be mixed with enough distilled water to adjust its specific gravity to 1.835
2. be sure to pour the acid into water never vice versa
3. be sure to pour the water into acid never vice versa
4. pure concentrated sulphuric acid is used as an electrolyte it does not need to be mixed
68. What is the specific gravity of fully charged lead acid battery (Dale Crane, P-23.
1. 1.260 to 1.285 at 800F 2. 1.260 to 1.28 at 1000F
3. 1.835 at 800F 4. 1.150 at 800F
69. In a nickel cadmium battery when is the electrolyte level is highest: (Dale Crane, P-8)
1. immediately after the battery has completed its charge
2. after the battery has been fully charged and allowed to rest for an hour or two 3. the electrolyte level does not change in a ni-cad battery
70. What is the function of the electrolyte in a nickel cadmium battery (Dale Crane, P-23. 1. serves as an active element in the chemical action generating the current
2. serves as a conductor only, and does not take part in the chemical action
3. serves only to keep the cell cool
4. serves as an indicator of the charge of the cell
71. How can you tell when a constant voltage charge of a nickel-cadmium battery is complete: (Dale Crane, P-23. 1. the voltage stop rising
2. the current decreases and stabilized
3. the specific gravity of electrolyte rise to 1.300 4. the cell voltage rises to 1.82 volts per cell
72. What type of battery charger is recommended for the final charge of nickel cadmium battery: (Dale Crane, P-24.
1. constant current charger
2. constant voltage charger
3. a/c gen. charging system in the airplane
4. charger which puts a low voltage alternating current across the battery
73. What may be used to neutralize spilled electrolyte from a nickel cadmium battery: (Dale Crane, P-24. 1. baking soda 2. ammonia 3. triehlorothene 4. vinegar
74. Fact relating to secondary cell is that: (Eismin P-31. 1. active material does not go into solution
2. it can be recharged and discharged many times before complete deterioration 3. active material undergoes chemical change during charging and discharging
4. all of the above are correct
75. One more negative plate in Pb-acid cell than positive plates is used in order to: (BLT Vol , P-353.
1. prevent positive plate from warping or buckling
2. increase the cell potential 3. increase the cell capacity
4. decreases the cells internal resistance
1. voltage of cell 2. specific gravity
3. amount of active material at cathodes 4. amount of active material at positive plate 77. In the a/c, storage battery is charged by: (Eismin P-47) 1. constant DC current 2. constant DC voltage
3. constant AC voltage 4. constant AC current
78. The specific gravity of electrolyte is measured by hydrometer. The correction of specific gravity is required at: (Eismin, P-41.
1. every time
2. when temperature is above or below 800F 3. when the temperature is above or below 600F
4. when the temperature exceeds 1400F
79. The e.m.f. of a battery is: (Eismin, P-43.
1. less than terminal voltage 2. equals terminal voltage
3. greater than the terminal voltage
4. less or more depends on direction of current flow
80. In different countries, the same rate of battery was charged, which gets more charge: (Eismin, P-41. 1. 00F, 1hr 2. 800F, 1hr 3. 600F, 1hr 4. 700F, 1 hr
81. A fully charged lead acid battery will not freeze until extremely low temperatures are reached because: (Eismin, P-39)
1. the acid is in the plates, thereby increasing the specific gravity of the solution
2. most of the acid is in the solution
3. increased internal resistance generates sufficient heat to prevent freezing 4. none of the above
82. What determines the amount of current which will flow through a battery will be able to charged by a constant
voltage source: (Eismin, P-62.
1. the total plate area of the battery
2. the state of charge of the battery
3. the ampere hour capacity of the battery 4. any of the above
83. In nickel cadmium battery, rise in cell temperature: (Eismin, P-47) 1. causes an increase in internal resistance
2. causes a decrease in internal resistance
3. increases cell voltage 4. none
84. In a constant current charging system a battery requires attention at the end of charge to avoid:(Eismin, P-47) 1. sulphation of battery
2. spilling of electrolyte 3. evaporation of electrolyte
4. danger of over charging
85. Electrolyte solution in ni-cad battery is: (Eismin, P-47) 1. 70% KOH & 30% of distilled water by weight
2. 30% KOH & 70% of distilled water by weight
3. 70% KOH & 30% of distilled water by volume 4. 30% KOH & 70% of distilled water by volume
86. The separators used for ni-cad battery is: (Eismin, P-47) 1. cedar wool
2. woven nylon fabric with a cellophone layer
3. micro porous plastic with cellophone layer 4. glass wool mixed with cellophone
87. Nickel-cadmium battery: (Eismin, P-52.
1. stored in only charged condition
2. can be stored in discharged condition for longtime
3. reduces capacity if stored in Hot condition 4. none
88. What is the neutralizing agent to be applied on skin when acid falls on it? (9A) 1. Potassium Hydroxide 2. Sodium Bicarbonate 3. Boric powder
89. Which of the following is correct for the Ni/ Cd battery (Eismin/46) 1. current delivering capacity less
2. it can not be discharged to zero voltage level 3. for same capacity of pb acid, its weight is high
4. its initial cost is relatively high
90. Horizontal ribs in Pb-acid cells (9A/308)
1. provide the cavity for fallen material 2. provide the cavity for electrolyte 3. enhance the rate of reaction 4. enhance the delivering rate of current 91 High rate of discharge in relation to battery means - (Eismin/50) 1. charging the battery at a very high rate
2. discharging the battery by employing a heavy load
3. discharging the battery by shorting the terminals 4. all are correct
92. What may result if water is added to nickel cadmium battery when it is not fully charged ? 9A/314, Eismin-40) 1. S.G of electrolyte decreases
2. Excessive spillage is likely to occur during the charging cycle
3. No adverse effects since water may be added any time 4. None of these
93 Battery is a source that - (Eismin/30)
1. generates emf by chemical action
2. converts mechanical energy into electrical energy 3. converts heat energy into electrical energy 4. None
94. Electrolyte used in NI-CAD battery is (Eismin/35)
1. 30% sulphuric acid + 70% water 2. caustic potash
3. nitric acid 4. none
95. During discharge of a lead acid battery, voltage of cell (9A/310)
1. decreases 2. increases 3. remains constant 4. none
96. While testing the specific gravity of the electrolyte of a nickel cadmium battery, it shows a reading of 1.300,
that means (9A /31A)
1. the battery is fully charged
2. the charging state can't be predicted
3. the battery is moderately charged 4. the battery has lesser charge
97. The purpose of providing bottom grooves underneath the plates in a lead acid cell container is to (Eismin/37) 1. allow for convection of the electrolyte for cooling of the plates
2. ensure that the electrolyte's quantity and plate area is adequate
3. prevent sediment build up from contacting the plates and causing a short circuit
4. prevent escape of electrolyte but allow
98. The separators used in lead acid battery have vertical ribs on the side (Eismin/37) 1. facing the positive plate
2. facing both the positive & negative plate
3. facing the negative plate
4. half part facing positive plate & half part facing negative plate
DC Circuits
99. Ohm’s law is applicable to (Eismin/13-14.
1. ac circuits only 2. dc circuits only 3. both, ac & dc circuits 4. none of these
100. Kirchhoff’s laws are applicable to ________ (Eismin 26-27) 1. Sinusoidal voltage only 2. d.c. voltage only
3. Voltage of any wave shape 4. none of the above
101. Kirchhoff’s voltage law is concerned with ______ (Eismin/26-27) 1. IR drops 2. battery emf. 3. Junction voltage 4. both 1 & 2.
102. In a Wheatstone bridge, the current through the galvanometer at balanced condition is _______. (Grob/177)
1. 1.08 A 2. 0.0A 3. 1.414 A 4. 1.732 A
103. For a fixed supply voltage, the current flowing through a conductor will increase when its: (Ref. FAA 9A, Pg. 283.
1. Area of cross-section is reduced 2. Length is reduced
3. Length is increased 4. Length is increased & cross sectional area is reduced
104. Specific resistance of a conductor depends: FAA 9A
1. Dimensions of the conductor 2. Composition of conductor material
3. Resistance of the conductor 4. All of the above
105. Which of the following materials possesses the least specific resistance (Ref. FAA 9A, Pg. 273.
1. Aluminum 2. Copper 3. Silver 4. Iron
106. In a series circuit: (Ref. FAA 9A, Pg. 206) 1. Current flowing through each resistor is same
2. Resistors are additive
3. Applied voltage is equal to sum of voltage drops across individual resistors
4. All of the above
107. Wheatstone bridge is useful for measuring ____. (Grob/172. 1. Very high resistance
2. Very low resistance
3. Medium range resistance 1Ω to 100 kΩ
4. None of the above
108. Kirchhoff’s laws are applicable to (Grob 258-269)
109. Kirchhoff's current law is applicable to (Grob/258) 1. closed loops in a network 2. electronic circuits
3. junction in a electric network 4. electric circuits
110. For doubling the current in a circuit of a constant resistance, the applied voltage must be: (BLT , P-9) 1. kept squared 2. doubled 3. halved 4. quadrupled
111. The polarity sign of an IR drop is primarily dependent upon (Grob/259) 1. amount of current flowing through it 2. value of R
3. direction of current flow 4. battery connection
112. In a circuit the voltage is doubled and the resistance is cut in half at the same time the current will be (9A/273 & Ohms laws)
1. doubled 2. a quarter 3. a half 4. four times as high
113. In a parallel circuit, all component must (Grob, 132.
1. have the same potential difference across them 2. have same value
3. carry equal current 4. all
114. Four 1.5V cells are connected in parallel. The output voltage is (9A, 276)
1. 1.0V 2. 1.5V 3. 6.0V 4. None
115. Which of the following statement is true both for a series and a parallel dc circuit? (Grob /164.
1. powers are additive 2. voltages are additive
3. currents are additive 4. elements have individual currents
Resistance /
Resistor-116. A good electric conductor is one that (BLT)
1. has low conductance 2. is always made of copper wire
3. produces a minimum voltage drop 4. has few free electrons
117. cylindrical wire, 1 m in length, has a resistance of 100 ohm. What would be the resistance of a wire made from the same material if both the length & cross-sectional area are doubled? (9A/273.
1. 200 ohms 2. 400 ohms 3. 100 ohms 4. 50 ohms 118. Factors affecting the resistance value is (9A/273.
1. cross sectional area 2. Length 3. Temperature 4. All
119. Ideal Constant voltage source has ____ internal resistance while practical constant current source has ___ internal resistance. (Grob, 375)
1. zero, very high 2. very low, very high 3. very low, infinity 4. zero, infinity
120. A linear resistor is defined as a resistor: (BLT Electronics, P-10) 1. whose value is independent of applied voltage
2. whose V-I characteristics is a straight line
3. whose current varies inversely with the applied voltage
4. both ‘1’ and ‘2’
121. If current through a resistor is halved, wattage developed by it would be: (BLT Electronics, P-74. 1. halved 2. quadrupled 3. cut to one-fourth 4. doubled
1. current rating 2. Ohmic value 3. voltage rating 4. tolerance
123. In a resistance, coded as per end-to-centre system of marking, if the third band is silver in colour, the first two
digits must be - (9A/280)
1. multiplied by 10% 2. multiplied by 1% 3. divided by 10% 4. divided by 1 % 124. Which of the following will cause the resistance of a conductor to decrease ? (9A/273. 1. increase the length or decrease the cross-sectional area
2. decrease the length or increase the cross sectional area
3. decrease the length or the cross sectional area 4. increase the length or the cross sectional area
125. Resistance of a wire is 4 ohms and is stretched to twice its length. The resistance now is – (Grob/50,51,52.
1. 4 ohms 2. 8 ohms 3. 12 ohms 4. 16 ohms
126. Carbon composition resistors are most popular because they (9A/352. 1. cost the least 2. are smaller in size
3. can withstand over loads 4. do not produce electric noise 127. Current and voltage in an a.c. resistive circuit are (9A/352.
1. 900 out of phase 2. in phase
3. 900 out of phase current leading voltage 4. 1800 out of phase.
128. The % tolerance for gold is (Grob/53,54.
1. ± 5% 2. ± 2% 3. ± 10% 4. ± 20%
129. In end-to- centre colour coding of resistance, if the colours are brown, black, red the value of resistance is (9A/352.
1. 100Ω 2. 1000 kΩ 3. 10Ω 4. 1 kΩ
130. A unique feature of wire wound resistor is its (Grob /57) 1. low power rating 2. very high stability
3. low cost 4. smaller size
131. The condition for ohm's law is related to (Eismin/13.
1. the temperature should remain constant
2. ratio V/I should be constant 3. the temperature should vary
4. current should be proportional to voltage
132. If a 12 volt circuit furnishes 3 amperes to a parallel circuit consisting of three equal resistors, what is the value of each individual resistor ? (Self made questions, Ohm laws)
1. 12 ohms 2. 4 ohms 3. 1.33 ohms 4. cannot be determined 133. Precision value resistance is composed of:- (GROB)
1. Copper 2. Gold 3. Carbon 4. Manganin
134. Carbon composition resisters are most popular because they …: (BLT Vol-I, P-49) 1. cost least
2. are smaller in size 3. can withstand over loads
4. both (a) and (b)
135. if there is no forth color band on the resistor, the tolerance is to be understood as: (9A, P-280)
1. 10% 2. 20% 3. 5 % 4. no tolerance
136. MTCS Rheostat has: (9A,P-296)
1. three terminals and controls current 1. two terminals and controls voltage 3. three terminals and controls voltage 4. two terminals and controls current
137. MTCS A potentiometer has: (9A,P-296)
1. two terminals and controls voltage 2. three terminals and controls current 3. two terminals and controls current 4. three terminals and controls voltage
138 The Current Voltage equation will be [FAA 9A, P-290]
1. IR1 + IR2 + IR3 = E1 - E2 +E3
2. I(R1 + R2 + R3 ) = E2 - E1 +E3
3. I(R1 + R2 + R3 ) = E3 - E1 –E2
4. IR1 + IR2 + IR3 = E1 + E2 –E3
Power
139. The ratio of resistances of a 100 Watt, 220 V lamp to that of a 100 Watt, 110 V lamp will be, at the
respective voltages (Ohm’s law)
1. 4:1 2. 2:1 3. 1:2 4. 1:4
140. A voltage drop is 100 volt across a 100 ohms resistance delivers (9A/284. 1.10,000 watts 2.1000 watts 3.100 watts 4.10 ampere
141. A 200 W, 230 V lamp is connected across 115 V supply. The lamp will draw power (Ohm’s law) 1. slightly more than 50 watts 2. slightly less than 50 watts
3. exactly 100 watts 4. exactly 50 watts
142. When adding a rheostat to a light circuit to control the light intensity, it should be connected (9A/296) 1. in parallel with the light 2. across the source of energy
3. in series with the light 4. in series-parallel with the light switch
Capacitance / Capacitor
143. The equivalent capacitance value, when three capacitor having same value, are connected in series, is (Eismin/10A)
1. 75 micro farad 2. 25 micro farad
3. one third of each value 4. three times the value of the capacitor
144. The charge of electricity that can be placed on capacitor is proportional to - (9A/350) 1. applied voltage and frequency 2. capacitance and frequency
3. applied voltage and capacitance 4. capacitive reactance 145. The working voltage of a capacitor in an a.c circuit should be (9A/351. 1. equal to the highest applied voltage
2. at least 20% greater than the highest applied voltage
3. at least 50% greater than the highest applied voltage
4. none of these
146. Capacitors are used to (Eismin/105)
1. block a.c. and pass d.c. 2. block dc and pass ac
3. pass a.c. and d.c. 4. block a.c. and d.c. 147. The dielectric strength is measured in terms of (9A/351.
1. breakdown voltage per unit thickness 2. breakdown voltage
R3
E1
R1
E2
R2
E3
I
3. current 4. watt
148. In one time constant, capacitor takes the charge up to ___ % of its full charge (Eismin/105)
1. 63.2 2. 36.7 3. 20.6 4. 80.2
149. Net power consumed by pure inductor or capacitor is _______ (BLT)
1. 2 watt 2. zero 3. 6 watt 4. none of these.
150. A capacitor has energy which is given by (9A)
1. ½ CV2 2. I2R 3. V2/R 4. none of the above
151. Coulomb per volt is the unit of (Grob/493,495,496)
1. inductance 2. inductive reactance 3. capacitance 4.capacitive reactance 152. Which of these items does not enter into determination of the capacity of a capacitor: (BLT , P-5. 1. thickness of the dielectric
2. material of which the plates are made
3. material of which the dielectric is made 4. area of the plates
153. The capacitive reactance decreases as the value of the capacitance increases because a large capacity capacitor
will (9A/352.
1. take less charge than low capacity capacitor
2. take greater charge than low capacity capacitor
3. require lower voltage than low capacity capacitor 4. require higher voltage than low capacity capacitor
154. When relatively high capacitance is required in a small capacitor we use (GROB-P- 503. 1. Ceramic capacitor 2. Paper capacitor
3. Electrolytic capacitor 4. Mica capacitor
155. When the capacitor is charged fully the value of the current in the circuit is: (Grob-P-338)
1. Zero 2. Maximum 3. Minimum 4. Moderate
156. The energy stored in a capacitor depends on: (GROB) 1. directly proportional To the area plate
2. inversely proportional to the distance between the plates 3. depends on dielectric
4. all of the above
157. The dielectric used in variable capacitor is: 9A
1. mica 2. paper 3. air 4. oil
158. The working voltage of capacitor depends on (9A/351. 1. frequency of voltage 2. thickness of dielectric
3. type of dielectric 4. all of the above
159. There is a greater possibility of voltage breakdown and leakage current in an electrolytic capacitor
because – (9A/349)
1. the electrolyte used is in a liquid or a paste form 2. the electrolyte is having a low dielectric strength
3. dielectric is a thin film of oxide
4. undesirable low frequency
160. Capacitors are said to: (Eismin- 106)
2. block DC and pass AC
3. pass AC and DC both 4. block AC and DC both
161. How many time constant needed by a capacitor to be charged upto 99.8%: (Eismin, P-105)
1. 06 2. 04 3. 07 4. 05
Magnetism-162. Whenever a magnet is quickly brought towards an open circuited stationary coil (Grob/425) 1. a current is induced in it 2. work has to be done
3. e.m.f. is induced in it 4. power is spent 163. Magnetism of a magnetic can be destroyed by (Grob/393. 1. heating 2. inductive action by other field 3. hammering 4. all of the above
164. Permanent magnets are normally made of – (Grob/388)
1. aluminium 2. wrought iron 3. cast iron 4. alnico alloys
165. In a magnetic material, hysteresis loss takes place primarily due to – (Grob/406)
1. flux density lagging behind magnetizing force
2. molecular friction 3. its high retentivity
4. rapid reversals of its magnetization
166. Soft magnetic materials have (Grob/403.
1. high permeability & low coercive force 2. low permeability & high coercive force 3. high residual magnetism 4. low resistivity
167. The property of a material which opposes the production of magnetic flux in it is known as (Grob/409) 1. mmf 2. reluctance 3. permeance 4. permittivity
168. The retentivity of magnetic material means (BLT/318)
1. residual magnetism 2. ability to remove the residual magnetism
3. ability to keep residual magnetism 4. ability to get magnetism
169. The soft iron piece is used as electromagnet because it has __ retentivity and ____ permeability (Jeppesen)
1. low, high 2. low, low 3. high, low 4. high, high
Inductance / Inductor
170. Inductance of a coil is determined by the (Jeppesen 3-51. 1. type of core 2. number of turns
3. shape and size of the coil 4. all of the above
171. Inductive reactance is measured in (Jeppesen 3-53.
1. Henry’s 2. Gilbert 3. Ohms 4. Farads
172. XL increases with increase in both (Jeppesen 3-53.
1. f & c 2. f & L 3. R & P 4. all of the above
173. Direction of the induced emf in a generator is determined by generator (Jeppesen 4-2.
3. both hand rule 4. none of these
174. A coil has an inductance of 1H if current is changing at the rate of 2 Ampere/sec induces:
(BLT Electronics, P-74. 1. one volt in it 2. two volts in another coil 3. two volts in it 4. half a volt in it
175. According to lenz’s law, the emf induced in a coil always ……. the cause: (9A-344. 1. assist
2. opposes
3. equate 4. none
176. When a coil carrying current produces magnetic field the field is(Eismin-P-9 & Grob-P-422.
1. Concentrated at the centre of coil 2. Spreads equally in the coil 3. Concentrated at the surface of length 4. None of the above
177. Higher the self induction of a coil – (Grob/577) 1. lower the emf. Induced in it
2. longer is the delay in establishing steady current through it
3. greater the flux produced by it 4. lesser the weber turns
178. The field at any point on the axis of a current carrying coil will be (BLT/264.
1. perpendicular to the axis 2. parallel to the axis 3. at an angle of 45 degree with the axis 4. zero
179. The force required to wipe out the residual magnetism is called (Grob/408) 1. retentivity 2. magnetizing force 3. coerceive force 4. permeability
180. For a given shape of a coil, the amount of inductance depends on – (BLT) 1. no. of turns 2. core
3. separation between the turns 4. all of these
181. If a magnetic material is used as the core of inductor, the property of material – (Grob/579) 1. decreases the inductive reactance 2. increases the permeability of coil
3. increases the inductance of the coil 4. decreases the inductance of the coil 182. Four inductor of 2µH is connected in series is the equivalent inductance (Grob/603. 1. 2µ h 2. 1/2 µH 3. 8µH 4. None
183. A coil with a certain number of turns has a specified time constant. If the number of turns is doubled,
its time constant would (Eismin/107)
1. remain unaffected 2. becomes doubled 3. becomes one fourth 4. get halved
DC Motor / Generator Theory
184. The dynamically induced emf. in a conductor does not depend on (self made)
1. its conductivity 2. flux density 3. the active length 4. its velocity 185. The induced emf when a conductor moves along the magnetic axis with very high speed is
(Grob/425/488/489) 1. maximum depending on different factors
2. zero because cutting flux is maximum
3. zero because rate of cutting of flux is negligible
4. some value
1. lies in a magnetic field
2. cuts magnetic flux
3. moves parallel to the direction of the magnetic field 4. lies perpendicular to the magnetic flux
187. In elementary d.c. generator, if no of coil is increased (Pallette/2. 1. induced emf. will increase
2. no. of ripple frequency will increase, resulting in steady dc
3. ripple will decrease 4. both 2. and 3.
188. Which of the following facts related to elementary d.c. generator is incorrect? (9A/297) 1. during the rotation, for instant, when coil's plane remains along MNA induced emf is minimum
2. in above case, when coil's plane is along magnetic neutral axis (MNA), induced emf is maximum
3. direction of current flow in coil direction of polarity of induced emf is given by Fleming left hand rule 189. In a self excited dc-generator, electromagnet instead of permanent magnet is used for necessary field
(BLT) 1. to change the field strength as per requirement
2. because with time strength of a magnet decreases 3. because its size is less
4. all of the above
190. In generator, induced emf depends on (BLT/302.
1. no. of turns 2. field strength 3. speed of armature 4. all of the above
191. In dc motors (9A/447/448)
1. net emf = applied voltage - counter emf 2. net emf = counter emf - applied emf 3. net emf = counter emf 4. net emf = applied voltage
192. Degree of compounding means the effect of ___ on ___ (BLT)
1. series field, terminal voltage 2. terminal voltage, series field 3. generated voltage, terminal voltage 4. shunt field, series field
193. If the terminal voltage is equal to no load voltage, generator is called 9A/396)
1.flat compound 2. cumulatively compound 3. differentially compound 4. either 2 or 3
194. In compound wound generators _____ field coil is of ____ conductor with ____ turns. (9A/396)
1. series, thick, a few 2. series, thin, many 3. series, thin, a few 4. series, thick, many
195. The effect of armature reaction may result in (9A/397) 1. pitted commutator surface 2. reduction in output voltage
3. enough wear on brushes 4. all of the above
196. The ____ motor is not started without mechanical load (9A/445/446)
1. d.c. series 2. shaded pole 3. induction 4. capacitor start
197. The part of a d.c. motor which changes the current flow from one wire to another is (9A/392.
1. yoke 2. brushes 3. armature 4. commutator
198. The field poles and armature in a d.c. generator are laminated in order to reduce its –(9A/391. 1. weight 2. speed 3. eddy current loss 4. hystresis loss
199. In d.c. generators, armature reaction is produced actually by – (9A/397) 1. its field current 2. armature conductors
3. field pole winding 4. load current in armature
200. If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shunt
field – (9A/39A)
1. to earth 2. to an a.c. source 3. to a d.c. source 4. either 2 or 3
201. A large series motor is never started without some mechanical load on it because (BLT) 1. draw too much current 2. develop excessive speed and damage itself
3. produce vicious sparking at brushes 4. open fuse or circuit breaker
202. Which generator is used when voltage is of prime importance ? (BLT)
1. series wound 2. shunt wound
3. compound wound 4. both 2 and 3
203. If a short circuit occurs between the positive armature lead and the field lead of a shunt generator which has the voltage regulator located in the positive side of the field circuit the -
1. generator voltage will drop to zero
2. generator will only produce residual voltage
3. reverse current cut out relay will open and remain open until the fault is corrected
4. generator voltage will increase
204. Generator inter poles: (Pallette/4.
1. Improve generator output 2. Prolong the life of the brushes & commutator 3. Reduces radio interference 4. All of the above
205. Iron loss is the combination of : (BLT/1168)
1. Copper and eddy current loss 2. Hysterisis and Eddy current loss
3. Copper & Hysterisis loss 4. Copper & Mechanical loss
206. A dc series motor is started on no load its speed is : (9A/445,446) 1. zero 2. normal 3. infinite 4. none
207. Which of the following motors gives a high starting torque. (BLT)
1. series motor 2. shunt motor 3. compound motor 4. none
208. Why is the air gap between the yoke and armature of an electric motor kept smaller – (BLT)
1. to achieve a stronger magnetic field 2. to avoid overheating of machine
3. both 1. & 2. 4. none
209. Eddy current can be reduced by (BLT/1168)
1. reducing the thickness of the conductor
2. replacing the solid core with several insulated thin metal plates
3. applying high frequency a.c.
4. simply using a mica layer between coil & core
210. Which one of the following generator is not used in a/c power generation system? (BLT) 1. shunt wound generator 2. series wound generator
3. compound wound generator
211. ‘When a current carrying conductor is placed in a magnetic field, it tends to rotate’ this principle is used in (BLT)
1. generator 2. motor 3. hotwire instrument 4. rectifier
212. When heavy starting torque is required, we use (BLT) 1. compound wound 2. shunt wound motor
3. series wound motor 4. d.c. motor
213. In a DC generator ripple can be reduced by adding (Jeppesen 4-4.
1. more loop 2. less loop 3. more resistance 4. none of these
214. The brushes connected with commutator is placed (9A/397) 1. 90º away from its neutral position 2. 180º away from its neutral position
3. in neutral position 4. 270º away from its neutral position
215. For a d.c. motor which of the following is wrong (BLT) 1. copper losses in field and armature winding 2. hysteresis losses in armature core
3. hysteresis losses in electromagnet 4. eddy current losses in magnetic core
216. The armature reaction, in d.c. generators is produced actually by – (9A/397) 1. its field current 2. armature conductors
3. field pole winding 4. load current in armature
217. The back emf. of a d.c motor – (BLT)
1. often exceeds the applied voltage 2. aids the applied voltage
3. helps in energy conversion 4. regulates its armature voltage
218. When a series motor is run without load, the speed may increase for above the normal speed, causing armature
to fly apart because (9A/394.
1. at starting there is no counter emf
2. counter emf is higher than the applied emf
3. counter emf remain sufficiently below the applied emf
4. applied emf remains sufficiently below the counter emf
219. Under varying conditions of speed and load the only practical method of maintaining a constant voltage output from an aircraft generator is to vary (9A/398)
1. the strength of the magnetic field
2. the number of conductors in the armature 3. the speed at which the armature rotates
4. the brush pressure on the commutator segments
220. In a generator, what eliminates any possible sparking to the brush guides caused by the movement of the
brushes within the holder – (FAA-9A)
1. brush spring tension
2. the brush pigtail
3. undercutting the mica on the commutator 4. lubricating the brush sides
221. To what depth is the mica insulation between the commutator bars of a d.c. generator, undercut is (BLT)
1. equal to the width of the mica
2. one half the width of the mica 3. equal to twice the width of the mica 4. none
222. The output of an elementary generator is represented by (Jeppesen 4-4)
1. sine curve 2. cos curve 3. parallel curve 4. none of these
223. The frame of a generator is (Jeppesen 4-5)
1. high permeable 2. low permeable 3. Nill permeable 4. all of the above
224. Commutator is made of (Jeppesen 4-6)
1. hard drawn copper segments 2. soft drawn copper segment 3. hard drawn anilco steel 4. all of the above
225. The raised portion of each commutator segment is called (Jeppesen 4-7) 1. lowerer 2. riser 3. cut portion 4. only 1 & 3
226. The adverse effect of armature reaction is minimized by : (Eismin, P-194. 1. shifting the brushes along the MNA
2. placing the inter poles
3. placing the compensating winding
4. all are correct
227. The effect of magnetic filed produced by current carrying armature conductors: (Eismin, P-194. 1. reduction of effective filed strength
2. distortion of field flux
3. sparking on the commentator and brushes
4. all are correct
228. Long shunt compound wound generator have: (BLT-Vol-II-P-988) 1. Series field across both armature and shunt field
2. Shunt field across both armature and series field
3. Shunt filed across armature only 4. Shunt field in series with inter poles
229. At no load a series D.C generator has e.m.f equal to : (General)
1. Maximum of rated voltage 2. Minimum of rated voltage
3. Maximum of rated voltage + IR drop 4. No induced e.m.f 230. Self exited generator has: (BLT-Vol-II-P-982.
1. Permanent magnet 2. Separate 4.C source
3. Electromagnetic coil which is magnetized by machines current itself
4. All
231. The main function of inter poles is to minimize______________ between the brushes and the commutator when the 4.c machine is loaded: . (BLT-Vol-II-P-962.
1. Friction 2. Current 3. Sparking 4. Wear and tear
232. The sole purpose of commutator in a d.c generator is: (BLT-VOL-II-P935) 1. To increase out put voltage 2. Reduce sparking at the brushes
3. Provide smoother out put 4. Convert the induced a.c into d.c
233. Brush wear increase at: (Pallet-P-10)
1. Low altitude 2. Higher altitude
3. In cloudy whether 4. In summer
234. How can the direction of rotation of a d.c. motor be changed ? (9A/448) 1. interchange the wires which connect the motor to the external power source
2. reverse the electrical connection to either the field or armature winding
3. rotate the brush assembly by 90 degree 4. remove the starting winding
235. Which shunt wound motor is suitable for (BLT)
1. operating landing gear 2. operating flaps & slats
236. Which one is not related for determining the amount of voltage produced in generator (BLT) 1. the number of magnetic lines of flux
2. the number of conductors cutting the flux
3. the size of the conductor cutting the flux
4. the speed at which the conductor cuts the flux
237. How does armature reaction cause brush arcing - (9A/397)
1. it moves the neutral plane away from the brush location
2. it decreases the spring pressure holding the brush into the commutator 3. it increases the output voltage of the generator
4. it decreases the current in the armature
238. If load on a DC shunt motor is increased, its speed is decreased primarily due to : (Jeppssen P-131. 1. increase in its flux 2. decrease in back emf
3. increase in armature current 4. increase in brush drop
239. The commutation process in a d.c generator basically involves (9A/397) 1. Passage of current from moving armature to a stationary
2. Reversal of current in an armature coil as it crosses MNA
3. both 1 & 2 4. none
240. In motor right hand rule the direction of the torque is denoted by (FAA 9A) 1. index finger 2. middle finger
3. thumb 4. none of these
241. In Generator left hand rule the direction of lines of magnetic flux is denoted by (Jeppesen)
1. fore finger 2. first finger 3. index finger 4. all of the above
242. When the flow of electrons in two wires is opposite, the resulting magnetic fields forces the wires (Jeppesen 4-29)
1. closer 2. apart 3. both 1 & 2 4. none of these 243. The armature of a typical DC motor and DC generator is
1. dissimilar 2. similar 3. not identical 4. both 1 & 3
244. To vary the speed of a shunt motor, a device used is (Jeppesen 4-31. 1. transistor 2. diode 3. rheostat 4. capacitor
245. When field current of a motor is increased the motor speed will (Jeppesen 4-31. 1. increase 2. decrease 3. remain same 4. none of these
246. The motor in which two field windings wound in opposite directions on the same pole to reverse the direction
of rotation is known as (Jeppesen 4-32.
1. shunt motor 2. series motor
3. same field motor 4. split field motor
247. When the current in field winding of series motor is increased then the current in armature winding will (Jeppesen 4-33.
1. decrease 2. increase
3. remain same 4. none of these
248.. What is the relationship between the desired voltage regulator setting and the ambient temperature in which the airplane is operated: (Dale Crane, P-23.
1. the colder the ambient temp, the lower the voltage should be set
3. ambient temp. has no bearing in the desired voltage of the charging system 4. the regulated voltage should be same regardless of the temperature
249. The brushes connected with commutator is placed (9A/397) 1. 90º away from its neutral position
2. 180º away from its neutral position 3. 270º away from its neutral position
4. in neutral position
250. The speed of a dc motor can be controlled by varying (9A/449) 1. field strength 2.Armature circuit resistance
3. Applied voltage 4. All of the above
251. The purpose of a growler test is to determine the presence of (Jeppesen) 1. an improper capacitor 2. a shorted armature
3. a broken field frame 4. a broken voltage regulator connection
252. Which one of the following parts is not essential for d.c. generator (9A/390/391. 1. armature 2. slip ring 3. split ring 4. commutator
253. In a type of DC generator, when load is increased, voltage increases and when the load is decreased, voltage also decreases, the generator can be (9A/394.
1. Shunt generator 2. Differential compound generator 3. Compound generator 4. Series generator
254. In a long shunt compound wound generator, the shunt field is connected in parallel with (9A/395) 1. Armature
2. Series field
3. Parallel combination of armature and series field
4. Series combination of armature and series field
255. The __________ dc generator has the poorest voltage regulation (BLT) 1. Over-compound 2. compound 3. Shunt 4. Series
256. Which of the following generator provides approximately constant voltage from no-load to full load (9A/396) 1. Series 2. Shunt 3. flat compound 4. Over compound
257. The armature torque of a dc motor is a function of its (9A/438) 1. pole flux 2. Armature current 3. Speed 4. Both 1 and 2
258. The speed of a dc motor can be controlled by varying (9A/449) 1. its flux 2.Armature circuit resistance
3. Applied voltage 4. All of the above
259. The level of compounding in a cumulatively-compound d.c. Generator is usually adjusted by (BLT)
1. alternating series field current 2. changing shunt field current 3. connecting it long-shunt 4. connecting it short - shunt
260. An electric motor is used for (9A/438)
1. Generating power 2. Changing mechanical energy to electrical
3. changing electrical energy to mechanical 4. increasing the energy put into it
261. The commutator segments are insulated from one other by (9A/397)
1. thin sheet of mica 2. using riser 3. hard drawn copper 4. pig tail
1. by field diverter above normal value 2. by field diverter below normal value 3. either 1. and 2. 4. none of the above
263. Series dc motors are used in a/c (9A/446)
1. as engine starter 2. for raising or lowering landing gear 3. for cow flaps 4. all of the above
264. In a d .c generator , the cause of rapid brush arcing may be (BLT) 1. imperfect contact 2. severe sparking
3. rough commutator surface 4. any of the above
265. The induced emf is max. if the conductor cuts the magnetic field at (9A/342.
1. 00 2. 450 3. 900 4. none
266. Series DC motor: LT-Vol-II-P-1015)
1. Field winding made of few turns of heavy wire 2. Poor voltage regulation
3. Both 1 & 2
4. None of the above
267. If a magnet is dropped through a current carrying coil it falls with: (Grob-P-581. 1. Uniform acceleration equal to g
2. Non uniform acceleration less than g
3. Uniform acceleration less than g 4. Uniform acceleration more than g
268. The basic requirement of d.c generator armature winding is that it must be: (BLT-VOL-II-P935) 1. A lap winding 2. A closed one
3. A wave winding 4. Either 2 and 3
269. The series field of a short shunt d.c generator is excited by _________current: (BLT-VOL-II-P936)
1. Shunt 2. Load 3. Armature 4. External
270. The …….. reverses the direction of current in generator or motor. [ISMIN, P-191] 1. Commutator 2. Bursh 3. Slip ring 4. commutator segment
271. Which motor is operated by both AC or DC voltage ? [EISMIN, P-183] 1. Repulsion 2. Universal 3. Split phase 4. capacitor
272. Compound motor is: (Ref. FAA 9A, Pg.447)
1. Shunt 2. Series 3. Combination of both 4. None
273. Starting torque in case of the shaded –pole motor is: (Ref. FAA 9A, Pg.455) 1. Very Weak 2. Power factor is low 3. Both 4. None
AC Theory
274. Power in any electrical circuit is
1. additive 2. substracted 3. multiplied 4. divided 275. Power is calculated in terms of and depends on (Eismin, Pg – 14)
1. R,I,V 2. Only V & I 3. Only R & V 4. Only I & R 276. Wheatstone bridge in balanced condition
2. all resistance will be constant 3. two resistance will be out of circuit 4. none of above
277. The direction of an a.c current (Grob, AAA, AA5) 1. keeps changing 2. can not be found 3. keeps reversing 4. is fixed 278. The effective voltage of a a.c. sine wave 200 peak-to-peak, is approximately (9A/343.
1. 70.7 volt 2. 141.4 volt 3. 63.7 volt 4. 127.4 volt 279. The r.m.s value of a sine wave is equal to (9A/343. 1. 0.637 X max. value 2. 0.707 X max. value
3. 0.506 X max. value 4. 1.414 X max. value
280. When current passes through a conductor, the resultant effect is (BLT) 1. a magnetic field is produced 2. magnetic as well as heating effect
3. only heating effect 4. only chemical effect
281. In aircraft, frequency of a.c. supply is (FAA-9A)
1. 800 Hz 2. 400 Hz 3. 200 Hz 4. 100 Hz
282. The time period of a sine wave of frequency 50 Hz. is ______ seconds. (Grob/452.
1. 0.02 2. 0.03 3. 0.04 4. 0.05
283. A sinusoidal ac voltage which undergoes 100 reversals of polarity per second has a frequency of ___ Hz. (Grob/455)
1. 50 2. 100 3. 150 4. 25
284. The rms value of a sinusoidal current is _____ times its maximum value. (Grob/452. 1. √3 2. √2 3. 1/√2 4. 1/√3
285. The average value of a symmetrical sinusoidal alternating current over whole cycle is (Grob/452.
1. Always positive 2. Zero 3. +5A 4. +2A
286. Time period of a 400 Hz. a.c. signal is – (Grob/452. 1. 20 milliseconds 2. 2.5 milliseconds
3. 25 milliseconds 4. 400 milliseconds
287. The greatest value attended during one half of the cycle is called the: (9A,P-343.
1. peak value 2. average value 3. RMS value 4. effect value 288. No. of alternations in a 50 Hz. a.c signal is (Grob/452.
1. 50 2. 100 3. 150 4. 200
289. The frequency of ac voltage has significant effect on - (BLT) 1. transformer 2. the speed of the synchronous motor
3. the resistor 4. both 1 and 2
290. Period of a quantity is defined as (Grob/457)
1. number of cycles pr second
2. time required to rise from zero to peak and back to zero
3. time taken to complete one cycle
4. maximum value of voltage or current is either positive or negative direction
291. Relation of actual power, reactive power and apparent power should be (Eismin/90)
1. App. Power2 = real power2 + reactive power2 2. App. Power = real power + reactive power
3. App. Power = real power – reactive power 4. App. Power = real power X reactive power
292. Power factor is the ratio of ____ to _____ (Eismin/90) 1. actual power, apparent power 2. resistance, impedance
3. both 1 and 2 are correct 4. reactive power, apparent power
293. What is meant by "current and voltage are in phase" (9A/343. 1. voltage and current are of the same magnitude
2. voltage and current have the same frequency 3. the voltage leads the current in time
4. voltage and current reach their max. and zero value at the same time
294. The chief disadvantage of a low power factor is that (BLT) 1. more power is consumed by the load
2. current required for a given load power is higher
3. active power developed by a generator exceeds its rated output capacity
4. heat generated is more than the desired amount
295. The power factor of a purely resistive circuit is - (Eismin/90)
1. zero 2. lagging 3. leading 4. unity
296. The max. & min. valued of power factor is – (Jeppesen)
1. 1 and 0 2. +1 and –1 3. +1 and -5 4.+ 5 and –5
297. Many of the larger transport a/c have been equipped with AC electrical system. The reason is (Eismin/210) 1. Easier to install 2. Less maintenance required
3. More efficient 4. All of the above
298. In Y-connected 3-phase a.c. supply (Pallette/35)
1. line current =1.73 x phase current 2. line voltage = phase voltage
3. line current = phase current 4. phase voltage =1.73 x line voltage
299. The r.m.s value of sinusoidal a.c current is equal to its value at an angle of (Pallette/35) 1. 90 degree 2. 45 degree 3. 30 degree 4. 90 degree
300. The input to an a.c circuit having power factor of 0.8 lagging is 20 kV1. The power drawn by the circuit is (BLT)
1. 12 kW 2. 20 kW 3. 16 Kw 4. 8 kW
301. If a capacitor is connected to an a.c. source the current _____ the source voltage by ____ (FAA 9A) 1. lags 900 2. lags 450 3. leads 900 4. none
302. Power is given by ______ in 3 phase alternator (BLT)
1. √3 VL IL COS θ 2. √3 VP IP cos θ
3. √3 VL IP COSθ 4. √3 VL IP cos θ
303. In AC circuit the product of voltage and current is known as: (BLT) 1. apparent power 2. real power 3. resistance power 4. power
304. It is the symbol of (Eismin-211.
1. Y connection 2. star connection
3. delta connection 4. both 1 & 2 are correct
305. Power Factor is defined as (Ref. FAA 9A, Pg. 358)
1. True power 2. true power 3.apparent power 4.reactive power
Apparent power real power reactive power true power
306. Calculate capacitive reactance of 400hz circuit having a capacitance of 50 microfarads: (Dale Crane, P-52.
1. 8 ohms 2. 0.008 ohms c 125 ohms 4. 12.5 ohms
Resistive (R), Capacitive (C) and Inductive (L) Circuits
-
307. Which statement is true regarding resonance in an a.c. circuit: (Dale Crane, P-52. 1. at resonance Z=Xc 2. at resonance Z=XL
3. at resonance Z=R 4. at resonance Z=Lc
308. For R-L-C series resonant circuit, the circuit current is (Grob/761/762/763. 1. maximum 2. equal to V/R 3. in phase with V 4. all of the above
309. For R-L-C series resonant circuit (9A/761 )
1. power factor is unity 2. impedance is minimum 3. net reactance is zero 4. all of the above
310. In series R-L-C circuit, voltage drop across capacitor and inductor have a phase difference of _____ degree (9A/761.
1. 1800 2. 900 3. 1200 4. 600
311. In series resonant circuit (9A/357)
1. XL = XC 2. XL > XC 3. XL < XC 4. XL x XC =1
312. The resonant frequency of a series R-L-C circuit depends, (9A/357)
1. R 2. L 3. C 4. both L & C
313. At resonance, for the series tank circuit, ___ is maximum (9A/357) 1. impedance 2. current 3. both 1 & 2 4. neither 1 nor 2
314. A parallel a.c. circuit in resonance will - (9A/357) 1. act like a resistor of low value
2. have a high impedance
3. have current in each section equal to the line current
4. have a high voltage developed across each inductive and capacitive section
315. At lower frequency than its resonance, in a series RLC circuit - (Grob/761-62-63.
1. power factor is leading 2. power factor is lagging 3. power factor is unity 4. power factor is negative
Transformers-316. what remains constant in transformers:
1. current 2. voltage 3. frequency 4. power 5. both 3 and 4
317. Power loss due to ohmic heating in a transformer is called: (9A/361. 1. magnetic loss 2. hysteresis loss
3. copper loss 4. eddy current loss
318. The transmission of power over long distances is done at :- (BLT)
1. high voltage 2. high current 3. high impedance 4. high frequency
319. Transformers are rated in kVA instead of kW because (BLT/1151. 1. Load power factor is often not know
2. kVA is fixed whereas kW depends on load-power factor
3. Total transformer loss depends on volt-ampere
4. It has become customary
320. Primary is subjected to 220 V & secondary is stepped down supposed to give an output of 11 V & primary current is 5 A & secondary current is 90 A, the stepped down transformer is –
1. 30 % 2. 40 % 3. 70 % 4. 90 % efficiency
321. The voltage transformation ratio is (BLT/1123.
1. E 1 / E 2 2. N 1 / N 2 3. E 2 / E 1 4. none
322. The no load current of a transformer in terms of full load current is usually – (BLT/1129/1130)
1. 1 to 3 % 2. 3 to 15 % 3. 9 to 12 % 4. 12 to 20 %
323. The iron loss has: (BLT1985-P-597)
1. Copper and eddy current loss 2. Hysteresis and eddy current loss
3. Copper and hysteresis loss 4. Copper and flux leakage loss
324. The principle of statically induced e.m.f is utilized in (BLT Pg-1029)
1. Transformer 2. Motor 3. Generator 4. both 2 & 3
325. Voltage across the secondary winding of a transformer is due to :- (9A/585)
1. self-induction 2. mutual induction
3. electrostatic induction 4. none of these
326. The main purpose of using core in a transformer is to :- (BLT/1116-17) 1. decrease iron losses
2. prevent eddy current loss 3. eliminate magnetic hysteresis
4. decrease reluctance of the common magnetic circuit
327. When load on secondary of the transformer is increased, the current in primary side will – (BLT/1129) 1. not be effected
2. increase
3. decrease
4. be the sum of no load current and excessive current drawn due to secondary winding
328. Electric power is transferred from one coil to the other coil in a transformer – (BLT/1116) 1. electrically 2. electro-magnetically 3. magnetically 4. physically
329. A transformer operates (BLT)
1. always at unity power factor 2. has its own power factor
3. at a power factor below a particular value
4. at power factor depending on the power factor of load
330. Which of the following is a correct statement about eddy current (BLT) 1. Eddy current improves the efficiency of a motor
2. eddy current heat up the metal part
3. eddy current used for arc welding 4. none
331. Which transformer must be constructed to measure the current of the circuit : (BLT/444. 1. power transformer 2. auto transformer
3. current transformer 4. air core transformer
332. In a transformer the sinusoidal emf – (BLT/1123. 1. lags the flux inducing it by 180 degree 2. lags the flux inducing it by 90 degree 3. leads the flux inducing it by 180 degree 4. leads the flux inducing it by 90 degree
333. If in a transformer the secondary turns are doubled and at the same time the primary voltage is reduced by half, then the secondary voltage will - (BLT/1123.
1. be halved 2. be four times as high
3. not change 4. be reduced to a quarter
334. Which of the statement given below is correct for the auto transformer (BLT/1187) 1. it has to separate windings connected in series externally
2. it has only one winding
3. it can only step down the voltage
4. it is most suitable for power transformation
335 By definition a step down transformer is one in which – (G rob/587)
1. secondary current is more than primary current
2. secondary turns are less than primary turns 3. secondary winding consists of thinner copper wire 4. secondary power is less than primary power
336. In a step up transformer, the power output is same as primary input power neglecting the losses, but (Grob/587)
1. current is increased in secondary
2. current increases & voltage decreases in secondary
3. current decreases & voltage increases in secondary
4. current & voltage both increase in secondary
337. The measure of how well the flux of the primary is coupled into the secondary is called- (Grob/583. 1. mutual inductance 2. self-inductance
3. coefficient of coupling 4. coefficient of excitation
338. In practical transformer, the coefficient of coupling is (Grob/583.
1. less than 1 2. more than 1 3. equal to 1 4. equal to nearly 100
339. Permeabilities of copper and aluminium (Jeppesen 3-10)
1. higher than iron 2. equal to iron
3. lower than iron 4. none of these
340. Lines of magnetic flux always search the (Jeppesen 3-10)
3. vertical path 4. horizontal path
341. Reluctance is the opposition in the circuit to the flow of (Jeppesen 3-12.
1. lines of magnetic flux 2. lines of electric flux
3. air 4. all of the above
342. A transformer transfers electric power from one circuit to another without changing its (BLT/117) 1. voltage 2. current 3. frequency 4. all of the above
343. A transformer in which the core surrounds a considerable portion of the winding is known as (BLT/1117) 1. core type transformer 2. shell type transformer
3. both 1 & 2 4. none of these
344. In a transformer the core is laminated and insulated to reduce the (BLT/1117)
1. eddy current loss 2. hysteresis loss 3. copper loss 4. all of the above
345. In a transformer if N2 > N1 i.e. K> 1 then the transformer is called (BLT/1123.
1. step down 2. step in 3. step up 4. none of these
346. In auto transformer, primary and secondary windings are (BLT/1186) 1. isolated by each other 2. not isolated from each other
3. 1 & 2 both 4. none of these
347. Ferrite cores commonly used at high frequencies to: (BLT Electronics, P-74. 1. increase core losses 2. decrease core losses
3. decrease inductance 4. increase resistance
348. The maximum efficiency of transformer occurs when: (BLT Vol-II, P-1082. 1. iron loss is zero 2. iron loss is less than copper loss
3. iron loss = copper loss 4. iron loss > copper loss
349. In auto transformer: (BLT Vol-II, P-1090)
1. power is transferred inductively and conductively 2. there is saving of copper
3. both ‘1’ and ‘2’
4. none
350. Current transformer is: (Eismin-P-168)
1. Step up 2. Step down 3. Transformation ratio is unity
351. Mark the correct statement: (Eismin-P-108) 1. Transformer works on mutual induction principle
2. It has eddy current and cu looses while in operation 3. Transformer cores are laminated
4. All are correct
352. Laminated core of transformers provides: (BLT-Vol-II-P-1117)
1. Low reluctance path to magnetic field
2. High reluctance path to magnetic field 3. Low reluctance path to a.c. field 4. High reluctance path to a.c. field
