ELECTRICAL ENGINEERING OBJECTIVE
QUESTIONS AND ANSWERS
Here we are providing electrical engineering mostly asked MCQ PDF,It is great collection of ITI and Diploma based mostly asked questions.It have following topics questions and answers-
1.Basic Electrical
2.Battery
3.Measurement
4.Electrical Machine
5.Cable
6.Electrostatics
7.Electromagnetic
8.Electrical Materials
9.Others
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Candidate who are preparing for electrical engineering PSUs jobs should be download it,It will be surely clear your doubts on basically basic electrical
ELECTRICAL ENGINEERING MOST IMPORTANT MCQ
1. The ratio of voltage and electric current in a closed circuit
a. remains constant b. varies c. increases d. falls Ans-c
2. The curve representing ohm's law is
a. sine function b. Linear c. a parabola d. a hyperbola Ans-b
3. The resistance of a conductor having length l area of cross section a and resistivity ρ is given as:
a. ρa/l b. ρl/a c. ρla d. l/ρ Ans-b
4. The resistance of wire varies inversely as
a. area of cross section b. length c. resistivity d. temperature Ans-a
5. Which of the following quantities are same in all parts of a series circuit?
a. voltage b. power c. current d. resistance Ans-c
6. Which of the following statements is false in case of a series circuit?
a. the voltage drop across each resister is same b. the current flowing through each resistor is the same c. applied voltage is equal to the sum of voltage drops across individual resistors are additive d.none Ans-b
7. A resistance of 30 ohm is connected across 240v supply. If a resistance R ohm is connected in parallel with 30ohm resistor across the same supply, the current drawn becomes triple of original one The unknown resistor R is
a. 15ohm b. 10ohm c. 5ohm d.30ohm Ans-a
8. Three resistors, each of R ohms, are connected to form a triangle. The resistance between any two terminals will be:
a. 2/3 R b. 3/2R c. R d. 3R Ans-a
9. Which of the following is not correct?
a. P=V/R^2 b. P=VI c. I=√ (P/R) d. V=√PR Ans
10. A 100W bulb is connected in series with a room heater. If now 100W bulb is replaced by a 40w bulb, the heater output will :
a. increase b. decrease c. remain the same Ans-b
11. The voltage applied across an electric iron is halved. The power consumption of the iron will be: a. one-half b. one-fourth c. 1/√2times d. three-fourth Ans-b
12. Resistance of 200w,250v lamp will be
a. 625ohm b. 1250ohm c.312.5ohm d.31.25ohm Ans-c
13. Two heaters rated at 1000w, 250v each are connected in series across a 250v, 50Hz ac supply. The total power drawn from the supply will be:
a. 1000w b. 500w c. 250w d.2000w Ans-b
14. A 200w, 100v lamp is to be operated on 250v supply. The additional resistance required to be connected in series will be:
a. 125ohm b. 50ohm c. 75ohm d.25ohm Ans-c
15. Kirchoff's laws are valid for
a. linear ckt only b. passive time invariant ckt c. non-linear ckt only d. both linear & non-linear ckt Ans-d
16. KCL is applicable only to
a. electric circuits b. electronic circuits c. junctions in a network d. closed loop in a network Ans-c 17. KVL is concerned with
a. IR drop b. battery emf c. junction node d. both a and b Ans-c
18. A wye arrangement of resistances has each resistance of 3ohm, the equivalent delta arrangement will have each resistance of values.
a. 9ohm b. 6ohm c. 3ohm d. 1ohm Ans-a
19. A battery is connected to a resistance causing a current of 0.5A in the circuit. The current drops to 0.4 when an additional resistance of 5? is connected in series . The current will drop to 0.2A when the resistance is further increased by
a. 10 ohm b. 15ohm c. 25ohm d.5 ohm Ans-c
20. Cells are connected in series in order to increase the
a. current capacity b. life of the cells c. voltage rating d. terminal voltage Ans-c
21. Cells are connected in parallel in order to increase
a. life of the cells b. efficiency c. current capacity d. voltage rating Ans-c
22. When two cells are connected in parallel , it should ensure that have
a. identical internal resistances b. equal emfs c. same ampere hour capacity Ans-b
23.The capacity of a battery is expressed in
a. amperes b. amperes-hour c. watts d. watt-hour Ans-b
24. A series resonant circuit implies
a. zero pf and maximum current b. unity pf and maximum current c. unity pf and minimum current d. zero pf and minimum current Ans-c
25. which one is classified as integrating instrument?
a. D'arsonval galvanometer b. ampere-hour meter c. ohm-meter d. ammeter Ans-b
26. Which of the following types of instrument is an integrating instrument? a. power factor meter b. energy meter c. watt meter d. frequency meter Ans-b
27. Voltmeter should be of very high resistance so that
a. its range is high b. Its accuracy is high c. it may draw current minimum possible d. its sensitivity is high Ans-c
28. If a voltmeter is connected like a ammeter in series with a load
a. the measurement reading will be too high b. Almost no current will flow in the circuit c. the meter will burn out d. an inadmissably high current will flow Ans-b
29. A multirange instrument (ammeter or voltmeter) has
a. Multiple shunt or series resistances inside the meter b. variable coil turns c. multi -coil arrangement d. any of the above Ans-a
30. The S.I. unit of power is
a. henry b. coulomb c. watt d. watt-hour Ans-c
31. Electric pressure is also called
a. resistance b. power c. voltage d. energy Ans-c
32 The substances whfch have a large number of free electrons and offer a low resistance are called
a. insulators b. inductors c. semi-conductors d. conductors Ans-d
33. Out of the following which is not a poor conductor ?
a. Cast iron b. Copper c. Carbon d. Tungsten Ans-b
34. Out of the following which is an insulating material ?
a. Copper b. Gold c. Silver d. Paper Ans-d
35. The property of a conductor due to which it passes current is called
a. resistance b. reluctance c. conductance d. inductance Ans-cc
36 . Conductance is reciprocal of
(a) resistance (b) inductance (c) reluctance (d) capacitance Ans-a
37. The resistance of a conductor varies inversely as
(a) length (b) area of cross-section (c) temperature (d) resistivity Ans-b
38. With rise in temperature the resistance of pure metals
(a) Increases (b) decreases (c) first increases and then decreases (d) remains constant Ans-a
39. With rise in temperature the resistance of semi-conductors
(a) decreases (b) increases (c) first increases and then decreases (d) remains constant Ans-a
40. The resistance of a copper wire 200 m long is 21 Q. If its thickness (diameter) is 0.44 mm, its specific resistance is around
(a) 1.2 x 10~8 Q-m (b) 1.4 x 10~8 Q-m (c) 1.6 x 10""8 Q-m (d) 1.8 x 10"8 Q-m Ans-c
41. Three resistances of 10 ohms, 15 ohms and 30 ohms are connected in parallel. The total resistance of the combination is
(a) 5 ohms (b) 10 ohms (c) 15 ohms (d) 55 ohms Ans-a
42. An instrument which detects electric current is known as
(a) voltmeter (b) rheostat (c) wattmeter (d) galvanometer Ans-d
43. In a circuit a 33 Q resistor carries a current of 2 A. The voltage across the resistor is
(a) 33 V (b) 66 v (c) 80 V (d) 132 V Ans-b
44. A light bulb draws 300 mA when the voltage across it is 240 V. The resistance of the light bulb is (a) 400 ohm (b) 600 ohm (c) 800 ohm (d) 1000 ohm Ans-c
45. The resistance of a parallel circuit consisting of two branches is 12 ohms. If the resistance of one branch is 18 ohms, what is the resistance of the other ?
(a) 18 ohm (b) 36 ohm (c) 48 ohm (d) 64 ohm Ans-b
46. Four wires of same material, the same cross-sectional area and the same length when connected in parallel give a resistance of 0.25 ohm. If the same four wires are connected is series the effective resistance will be
(a) 1 ohm (b) 2 ohm (c) 3 ohm (d) 4 ohm Ans-d
47. A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is
(a) 6.4 A, 6.9 A (b) 6.4 A, 9.6 A (c) 4.6 A, 6.9 A (d) 4.6 A, 9.6 A Ans-b
48. Current velocity through a copper conductor is
(a) the same as propagation velocity of electric energy (b) independent of current strength (c) of the order of a few micro second (d) nearly 3 x 108 m/s Ans-c
49. Which of the following material has nearly zero temperature co-efficient of resistance?
(a) Manganin (b) Porcelain (c) Carbon (d) Copper Ans-a
50. You have to replace 1500 ohm resistor in radio. You have no 1500 ohm resistor but have several 1000 ohm ones which you would connect
(a) two in parallel (b) two in parallel and one in series (c) three in parallel (d) three in series Ans-b 51. Two resistors are said to be connected in series when
(a) same current passes in turn through both (b) both carry the same value of current (c) total current equals the sum of branch currents (d) sum of IR drops equals the applied e.m.f. Ans-a
52. Which of the following statement is true both for a series and a parallel D.C. circuit?
(a) Elements have individual currents (b) Currents are additive (c) Voltages are additive (d) Power are additive Ans-d
53. Which of the following materials has a negative temperature co-efficient of resistance?
(a) Copper (b) Aluminum (c) Carbon (d) Brass Ans-c
54. Ohm's law is not applicable to
(a) vacuum tubes (b) carbon resistors (c) high voltage circuits (d) circuits with low current densities Ans-a
55. Which is the best conductor of electricity ?
(a) Iron (b) Silver (c) Copper (d) Carbon Ans-b
56. For which of the following 'ampere second' could be the unit ?
(a) Reluctance (b) Charge (c) Power (d) Energy Ans-b
57. All of the following are equivalent to watt except
(a) amperes square ohm (b) joules/sec. (c) amperes x volts (d) amperes/volt Ans-d
58. A resistance having rating 10 ohms, 10W is likely to be a
(a) metallic resistor (b) carbon resistor (c) wire wound resistor (d) variable resistor Ans-c
59. Which one of the following does not have negative temperature co-efficient ?
(a) Aluminium (b) Paper (c) Rubber (d) Mica Ans-a
60. Varistors are (a) insulators (b) non-linear resistors (c) carbon resistors (d) resistors with zero temperature coefficient Ans-b
61. Insulating materials have the function of
(a) preventing a short circuit between conducting wires (b) preventing an open circuit between the voltage source and the load (c) conducting very large currents (d) storing very high currents Ans-a
62. The rating of a fuse wire is always expressed in
(a) ampere-hours (b) ampere-volts (c) kWh (d) amperes Ans-d
63. The minimum charge on an ion is
(a) equal to the atomic number of the atom (b) equal to the charge of an electron (c) equal to the charge of the number of electrons in an atom zero Ans-b
64. In a series circuit with unequal resistances
(a) the highest resistance has the most of the current through it (b) the lowest resistance has the highest voltage drop (c) the lowest resistance has the highest current (d) the highest resistance has the highest voltage drop Ans-c
65. The filament of an electric bulb is made of
(a) carbon (b) aluminium (c) tungsten (d) nickel Ans-c
66. A 3 ohm resistor having 2 A current will dissipate the power of
(a) 2 watts (b) 4 watts (c) 6 watts (d) 12 watts Ans-d
67. Which of the following statement is true?
(a) A galvanometer with low resistance in parallel is a voltmeter (b) A galvanometer with high resistance in parallel is a voltmeter (c) A galvanometer with low resistance in series is an ammeter (d) A galvanometer with high resistance in series is an voltmeter Ans
68. The resistance of a few metres of wire conductor in closed electrical circuit is
(a) practically zero(b) low(c) high (d) very high Ans-a
69. If a parallel circuit is opened in the main line, the current
(a) increases in the branch of the lowest resistance (b) increases in each branch (c) is zero in all branches (d) is zero in the highest resistive branch Ans-c
70. If a wire conductor of 0.2 ohm resistance is doubled in length, its resistance becomes
(a) 0.4 ohm (b) 0.6 ohm (c) 0.8 ohm (d) 1.0 ohm Ans-a
71. Three 60 W bulbs are in parallel across the 60 V power line. If one bulb burns open
(a) there will be heavy current in the main line (b) rest of the two bulbs will not light (c) all three bulbs will light (d) the other two bulbs will light Ans-b
72. The four bulbs of 40 W each are connected in series with a battery across them, which of the following statement is true ?
(a) The current through each bulb in same (b) The voltage across each bulb is not same (c) The power dissipation in each bulb is not same (d) None of the above Ans-a
73. Two resistances Rl and R2 are connected in series across the voltage source where R2>R1. The largest drop will be across (a) R2 (b) R1 (c) either Rl or R2 (d) none of them Ans-a
74. What will be energy used by the battery if the battery has to drive 6.28 x 1018 electrons with potential difference of 20 V across the terminal ?
(a) 5 joules (b) 10 joules (c) 15 joules (d) 20 joules Ans-d
75. A closed switch has a resistance of
(a) zero (b) about 50 ohms (c) about 500 ohms (d) infinity Ans-a
76. The hot resistance of the bulb's filament is higher than its cold resistance because the temperature co-efficient of the filament is
(a) zero (b) negative (c) positive (d) about 2 ohms per degree Ans-c
77. Heat in a conductor is produced on the passage of electric current due to
(a) reactance (b) capacitance (c) impedance (d) resistance Ans-d
78. The insulation on a current carrying conductor is provided
(a) to prevent leakage of current (b) to prevent shock (c) both of above factor (d) none of above factors Ans-c
79. The thickness of insulation provided on the conductor depends on
(a) the magnitude of voltage on the conductor (b) the magnitude of current flowing through it (c) both (a) and (b) (d) none of the above Ans-a
80. Which of the following quantities remain the same in all parts of a series circuit ?
(a) Voltage (b) Current (c) Power (d) Resistance Ans-b
81. A 40 W bulb is connected in series with a room heater. If now 40 W bulb is replaced by 100 W bulb, the heater output will (a) decrease (b) increase (c) remain same (d) heater will burn out Ans-b
82. In an electric kettle water boils in 10 minutes. It is required to boil the boiler in 15 minutes, using same supply mains
(a) length of heating element should be decreased (b) length of heating element should be increased (c) length of heating element has no effect on heating if water (d) none of the above Ans-a
83. An electric filament bulb can be worked from
(a) D.C. supply only (b) A.C. supply only (c) Battery supply only (d) All above Ans-d
84. Resistance of a tungsten as applied voltage increases
(a) decreases (b) increases (c) remains same (d) none of the above Ans-b
85. Electric current passing through the circuit produces
(a) magnetic effect (b) luminous effect (c) thermal effect (d) chemical effect (e) all above effects Ans-c
86. Resistance of a material always decreases if
(a) temperature of material is decreased (6) temperature of material is increased (c) number of free electrons available become more (d) none of the above is correct Ans: c
87. If the efficiency of a machine is to be high, what should be low ?
(a) Input power (b) Losses (c) True component of power (d) kWh consumed (e) Ratio of output to input Ans: b
88. When electric current passes through a metallic conductor, its temperature rises. This is due to
(a) collisions between conduction electrons and atoms (b) the release of conduction electrons from parent atoms (c) mutual collisions between metal atoms (d) mutual collisions between conducting electrons Ans: a
89. Two bulbs of 500 W and 200 W rated at 250 V will have resistance ratio as
(a) 4 : 25 (b) 25 : 4 (c) 2 : 5 (d) 5 : 2 Ans: c
90. A glass rod when rubbed with silk cloth is charged because
(a) it takes in proton (b) its atoms are removed (c) it gives away electrons (d) it gives away positive charge Ans: c
91. Whether circuit may be AC. or D.C. one, following is most effective in reducing the magnitude of the current.
(a) Reactor (b) Capacitor (c) Inductor (d) Resistor Ans: d
92. It becomes more difficult to remove
(a) any electron from the (6) first electron from the orbit (c) second electron from the orbit (d) third electron from the orbit Ans: d
93. When one leg of parallel circuit is opened out the total current will
(a) reduce (b) increase (c) decrease (d) become zero Ans: c
94. In a lamp load when more than one lamp are switched on the total resistance of the load
(a) increases (b) decreases (c) remains same (d) none of the above Ans: b
95. Two lamps 100 W and 40 W are connected in series across 230 V (alternating). Which of the following statement is correct ?
(a) 100 W lamp will brighter (b) 40 W lamp will glow brighter (c) Both lamps will glow equally bright (d) 40 W lamp will fuse Ans: b
96. Resistance of 220 V, 100 W lamp will be (a) 4.84 Q (b) 48.4 Q (c) 484 ft (d) 4840 Q Ans: c
97. In the case of direct current
(a) magnitude and direction of current remains constant (b) magnitude and direction of current changes with time (c) magnitude of current changes with time (d) magnitude of current remains constant Ans: a
98. When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is
(a) A.C. (b) D.C. (c) any of above two (d) none of the above Ans: b
99. Resistance of carbon filament lamp as the applied voltage increases.
(a) increases (b) decreases (c) remains same (d) none of the above Ans: b
100. Bulbs in street lighting are all connected in
(a) parallel (b) series (c) series-parallel (d) end-to-end Ans: a
101. For testing appliances, the wattage of test lamp should be
(a) very low (b) low (c) high (d) any value Ans: c
102. Switching of a lamp in house produces noise in the radio. This is because switching operation produces
(a) arcs across separating contacts (b) mechanical noise of high intensity (c) both mechanical noise and arc between contacts (d) none of the above Ans: a
103. Sparking occurs when a load is switched off because the circuit has high .(a) resistance (b) inductance (c) capacitance (d) impedance Ans: b.
104. Copper wire of certain length and resistance is drawn out to three times its length without change in volume, the new resistance of wire becomes
(a) 1/9 times (b) 3 times (c) 9 times (d) unchanged Ans: c
105. When resistance element of a heater fuses and then we reconnect it after removing a portion of it, the power of the heater will
(a) decrease (b) increase (c) remain constant (d) none of the above Ans: b
106. A field of force can exist only between
(a) two molecules (b) two ions (c) two atoms (d) two metal particles Ans: b
107. A substance whose molecules consist of dissimilar atoms is called
(a) semi-conductor (b) super-conducto (c) compound (d) insulator Ans: c
108. International ohm is defined in terms of the resistance of
(a) a column of mercury (b) a cube of carbon (c) a cube of copper (d) the unit length of wire Ans: a
109. Three identical resistors are first connected in parallel and then in series. The resultant resistance of the first combination to the second will be
(a) 9 times (b) 1/9 times (c) 1/3 times (d) 3 times Ans: b
110. Which method can be used for absolute measurement of resistances ?
(a) Lorentz method (b) Releigh method (c) Ohm's law method (d) Wheatstone bridge method Ans: d 111. 3 6 ohm resistors are connected to form a triangle. What is the resistance between any two corners ?
(a) 3/2 Q (b 6 Q (c) 4 Q (d) 8/3 Q Ans: c
112. Ohm's law is not applicable to
(a) semi-conductors (b) D.C. circuits (c) small resistors (d) high currents Ans: a
113. Two copper conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 40 ohms the resistance of other conductor will be
(a) 160 ohms (b) 80 ohms (c) 20 ohms (d) 10 ohms Ans: d
114. A nichrome wire used as a heater coil has the resistance of 2 £2/m. For a heater of 1 kW at 200 V, the length of wire required will be
(a) 80 m (b) 60 m (c) 40 m (d) 20 m Ans: a
115. Temperature co-efficient of resistance is expressed in terms of
(a) ohms/°C (b) mhos/ohm°C (e) ohms/ohm°C (d) mhos/°C Ans: c
116. Which of the following materials has the least resistivity ?
(a) Zinc (b) Lead (c) Mercury (d) Copper Ans: d
117. When current flows through heater coil it glows but supply wiring does not glow because
(a) current through supply line flows at slower speed (b) supply wiring is covered with insulation layer (c) resistance of heater coil is more than the supply wires (d) supply wires are made of superior material Ans: c
118. The condition for the validity under Ohm's law is that
(a) resistance must be uniform (b) current should be proportional to the size of the resistance (c) resistance must be wire wound type (d) temperature at positive end should be more than the temperature at negative end Ans: a
119. Which of the following statement is correct ?
(a) A semi-conductor is a material whose conductivity is same as between that of a conductor and an insulator (b) A semi-conductor is a material which has conductivity having average value of conductivity of metal and insulator (c) A semi-conductor is one which conducts only half of the applied voltage (d) A semi-conductor is a material made of alternate layers of conducting material and insulator Ans: a
120. A rheostat differs from potentiometer in the respect that it
(a) has lower wantage rating (b) has higher wattage rating (c) has large number of turns (d) offers large number of tappings Ans: b
121. The weight of an aluminium conductor as compared to a copper conductor of identical cross-section, for the same electrical resistance, is
(a) 50% (b) 60% (c) 100% (d) 150% Ans: a
122. An open resistor, when checked with an ohm-meter reads
(a) zero (b) infinite (c) high but within tolerance (d) low but not zero Ans: b
123. are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.
(a) Varistors (b) Thermistor (c) Semi-conductors (d) Variable resistors Ans: c
124. All good conductors have high
(a) conductance (b) resistance (c) reluctance (d) thermal conductivity Ans: a
125. Voltage dependent resistors are usually made from
(a) charcoal (b) copper (c) nichrome (d) graphite Ans: c
126. Voltage dependent resistors are used
(a) for inductive circuits (6) to supress surges (c) as heating elements (d) as current stabilizers Ans: b
127. The ratio of mass of proton to that of electron is nearly
(a) 1840 (b) 1840 (c) 30 (d) 4 Ans: a
128. The number of electrons in the outer most orbit of carbon atom is
(a) 3 (b) 4 (c) 6 (d) 7 Ans: b
129. With three resistances connected in parallel, if each dissipates 20 W the total power supplied by the voltage source equals
(a) 10 W (b) 20 W (c) 40 W (d) 60 W Ans: d
130. A thermistor has
(a) positive temperature coefficient (b) negative temperature coefficient (c) zero temperature coefficient (d) variable temperature coefficient Ans: c
131. If, R and t are the current, resistance and time respectively, then according to Joule's law heat produced will be proportional to
(a) I2Rt (b) I2Rf (c) I2R2t (d) I2R2t* Ans: a
132. Nichrome wire is an alloy of
(a) lead and zinc (b) chromium and vanadium (c) nickel and chromium (d) copper and silver Ans: c 133. When a voltage of one volt is applied, a circuit allows one microampere current to flow through it.The conductance of the circuit is
(a) 1 n-mho (b) 106 mho (c) 1 milli-mho (d) none of the above Ans: a
134. Which of the following can have negative temperature coefficient ?
(a) Compounds of silver (6) Liquid metals (c) Metallic alloys (d) Electrolytes Ans: d.
135. Conductance : mho ::
(a) resistance : ohm (b) capacitance : henry (c) inductance : farad (d) lumen : steradian Ans: a
136. 1 angstrom is equal to (a) 10-8 mm (6) 10"6 cm (c) 10"10 m (d) 10~14 m Ans: c
137. One newton metre is same as
(a) one watt (b) one joule (c) five joules (d) one joule second Ans: b
138. The force between two charges is 120 N. If the distance between the charges is doubled, the force will be
(a) 60 N (b) 30 N (c) 40 N (d) 15 N Ans: b
139. The electric field intensity at a point situated 4 metres from a point charge is 200 N/C. If the distance is reduced to 2 metres, the field intensity will be
(a) 400 N/C (b) 600 N/C (c) 800 N/C (d) 1200 N/C Ans: c
140. The lines of force due to charged particles are
(a) always straight(b) always curved (c) sometimes curved(d) none of the above Ans: b
141. The electric field at a point situated at a distance d from straight charged conductor is (a) proportional to d (b) inversely proportional to d (c) inversely proportional to d (d) none of the above Ans: b
142. The direction of electric field due +0 positive charge is . (a) away from the charge (b) towards the charge (c) both (a) and (b) (d) none of the above Ans: a
143. A field line and an equipotential surface are (a) always parallel(b) always at 90° (c) inclined at any angle 0(d) none of the above Ans: b
144. The ability of charged bodies to exert force on 6ne another is attributed to the existence of (a) electrons (b) protons (c) neutrons (d) electric field Ans: d
145. If the sheet of a bakelite is inserted between the of an , the capacitance will
(a) decrease (b) increase (c) remains unchanged (d) become zero Ans: b
146. A capacitor stores 0.24 coulombs at 10 volts. Its capacitance is
(a) 0.024 F (b) 0.12 F (c) 0.6 F (d) 0.8 F Ans: a
147. For making a capacitor, it is better to select a dielectric having (a) low permittivity (b) high permittivity (c) permittivity same as that of air (d) permittivity slightly more than that of air Ans: b 148. The units of capacitance are (a) volts/coulomb (b) coulombs/volt (c) ohms (d) henry/Wb Ans: b 149. If three 15 uF capacitors are connected in series, the net capacitance is (a) 5 uF (6) 30 uF (c) 45 uF (d) 50 uF Ans: a
150. If three 10 uF capacitors are connected in parallel, the net cararitance is
(a) 20 uF (b) 30 uE (c) 40 uF (d) 50 uF Ans: b
151. A dielectric material must be (a) resistor (b) insulator (c) good conductor (d) semi conductor Ans: b
152. An electrolytic capacitor can be used for
(a) D.C. only (b) AC. only (c) both D.C. as well as A.C. Ans: a
153. The capacitance of a capacitor is not affected by (a) distance between plates (6) area of plates (c) thickness of plates (d) all of the above Ans: c
154. Which of the following is not a vector ? (a) Linear momentum (b) Angular momentum (c) Electric field (d) Electric potential Ans: b
155. Two plates of a parallel capacitor after being charged from a constant voltage source are separated apart by means of insulated handles, then the
(a) Voltage across the plates (b) voltage across the plates decreases (c) charge on the capacitor decreases (d) charge on the capacitor increases Ans: b
156. If A.C. voltage is applied to capacitive circuit, the alternating current can flow in the circuit because
(a) varying voltage produces the charging and dicharging currents (b) of high peak value (c) charging current can flow (d) discharge current can flow Ans: a
157. Voltage applied across a ceramic dielectric produces an electrolytic field 100 times greater than air. What will be the value of dielectric constant ? (a) 50 (b) 100 (c) 150 (d) 200 Ans: b
158. Which of the following statements is correct ?
(a) Air capacitors have a blackband to indicate the outside foil (6) Electrolytic capacitor must be connected in the correct polarity. (c) Ceramic capacitors must be connected in the correct polarity (d) Mica capacitors are available in capacitance value of 1 to 10 pF Ans: b
159. The dissipation factor of a good dielectric is of the order of
(a) 0.0002 (b) 0.002 (c) 0.02 (d) 0.2 Ans: a
160. "The total electric flux through any closed surface surrounding charges is equal to the amount oflcharge enclosed".The above statement is associated with
(a) Coulomb's square law (b) Gauss's law (c) Maxwell's first law (d) Maxwell's second law Ans: b 161. Three capacitors each of the capacity C are given. The resultant capacity 2/3 C can be obtained by using them
(a) all in series (b) all in parallel (c) two in parallel and third in series with this combination (d) two in series and third in parallel across this combination Ans: c
162. For which of the following parameter variation, the capacitance of the capacitor remains unaffected ?
(a) Distance between plates (b) Area of the plates (c) Nature of dielectric (d) Thickness of the plates Ans: d
163. Which of the following statement is true ?
(a) The current in the discharging capacitor grows linearly (b) The current in the dicharging capacitor grows exponentially (c) The current in the discharging capacitor decays exponentially (d) The current in the discharging capacitor decreases constantly Ans: b
164. Which of the following expression is correct for electric field strength ?
(a) E = D/E (b) E = D2/t (c) E = jtD (d) E= nD2 Ans: a
165. In a capacitor the electric charge is stored in
(a) metal plates (b) dielectric (c) both (a) and (6) (d) none of the above Ans: b
166. Which of the following materials has the highest value of dielectric constant?
(a) Glass (b) Vacuum (c) Ceramics (d) Oil Ans: c
167.Which of the following capacitors will have the least variation ?
(a) Paper capacitor (b) Ceramic capacitor (c) Silver plated mica capacitor (d) None of the above Ans:c
168. Which of the following statements is incorrect ?
(a) The leakage resistance of ceramic capacitors is generally high (b) The stored energy in a capacitor decreases with reduction in value of capacitance (c) The stored energy in a capacitor increases with applied voltage (d) A wire cable has distributed capacitance between the conductors Ans: b
169. Which of the following capacitors has relatively shorter shelf life ?
(a) Mica capacitor (b) Electrolytic capacitor (c) Ceramic capacitor (d) Paper capacitor Ans: b
170. The sparking between two electrical contacts can be reduced by inserting a
(a) capacitor in parallel with contacts (6) capacitor in series with each contact (c) resistance in line (d) none of the above Ans: a
171. In the case of a lossy capacitor, its series equivalent resistance value will be (a) small (b) very small (c) large (d) zero Ans: c
172. The power dissipated in a pure capacitor is
(a) zero (6) proportional to applied voltage (c) proportional to value of capacitance (d) both (b) and (c) above Ans: a
173. In a capacitive circuit (a) a steady value of applied voltage causes discharge (b) an increase in applied voltage makes a capacitor charge (c) decrease in applied voltage makes a capacitor charge (d) none of the above Ans: b
174. When a dielectric slab is introduced in a parallel plate capacitor, the potential difference between plates will
(a) remain uncharged (b) decrease (c) increase (d) become zero Ans: b
175. Capacitance increases with
(a) increase in plate area and decrease in distance between the plates (b) increase in plate area and distance between the plates (c) decrease in plate area and value of applied voltage (d) reduction in plate area and distance between the plates Ans: a
176. A capacitor consists of (a) two insulators separated by a conductor (b) two conductors separated by an insulator (c) two insulators only (d) two conductors only Ans: b
177. A paper capacitor is usually available in the form of
(a) tubes (b) rolled foil (c) disc (d) meshed plates Ans: b
178. Air capacitors are generally available in the range (a) 10 to 400 pF (b) 1 to 20 pF (c) 100 to 900 pF (d) 20 to 100 pF Ans: a
179. The unit of capacitance is (a) henry (b) ohm (c) farad (d) farad/m Ans: c
180. A capacitor charged to 200 V has 2000 (iC of charge. The value of capacitance will be
(a) 10 F (6) 10 uF (c) 100 nF (d) 1000 uF Ans: b
181. A capacitor in a circuit became hot and ultimately exploded due to wrong connections, which type of capacitor it could be ?
(a) Paper capacitor (b) Ceramic capacitor (c) Electrolytic capacitor (d) Any-of the above Ans: c
182. Energy stored in the electric field of a capacitor C when charged from a D.C source of voltage V is equal to joules
(a) CV2 (b) C2V (c) CV2 (d) CV Ans: a
183. The absolute permittivity of free space is given by
(a) 8.854 x 1(T9 F/m) (6) 8.854 x 1(T10 F/m) (c) 8.854 x KT11 F/m (d) 8.854 x 10"12 F/m Ans: b 184. The relative permittivity of free space is given by (a) 1 (b) 10 (c) 100 (d) 1000 Ans: a
185. Electric field intensity is a quantity
(a) scalar (b) vector (c) both (a) and (6) (d) none of the above Ans: b
186. When 4 volts e.m.f. is applied across a 1 farad capacitor, it will store energy of
(a) 2 joules (b) 4 joules (c) 6 joules (d) 8 joules Ans: d
187. The capacitor preferred for high circuits is
(a) air capacitor (b) mica capacitor (c) electrolytic capacitor (d) none of the above Ans: b
188. The capacity of capacitor bank used in power factor correction is expressed in terms of
(a) kW (b) kVA (c) kVAR (d) volts Ans: c
189. While testing a capacitor with ohm-metre, if the capacitor shows charging, but the final resistance reading is appreciably less than normal, it can be concluded that the capacitor is
(a) short-circuited (b) open circuited (c) alright (d) leaky Ans: d
190. If a 6 mF capacitor is charged to 200 V, the charge in coulombs will be
(a) 800 uC (b) 900 uC (c) 1200 uC (d) 1600 uC Ans: c
191. Which capacitor will be physically smaller for the same ratings ?
(a) Ceramic capacitor (b) Paper capacitor (c) Both will be of equal size (d) None of the above Ans: a 192. What is the value of capacitance that must be connected in parallel with 50 pF condenser to make an equivalent capacitance of 150 pF ? (a) 50 pF (b) 100 pF (c) 150 pF (d) 200 pF Ans: b
193. A mica capacitor and a ceramic capacitor both have the same physical dimensions. Which will have more value of capacitance ?
(a) Ceramic capacitor (b) Mica capacitor (c) Both will have identical value of capacitance (d) It depends on applied voltage Ans: a
194. Which of the following material has least value of dielectric constant ?
(a) Ceramics (b) Oil (c) Glass (d) Paper Ans: b
195. Which of the following capacitors will have the least value of breakdown voltage ? (a) Mica (b) Paper (c) Ceramic (d) Electrolytic Ans: d
196. The breakdown voltage for paper capacitors is usually
(a) 20 to 60 volts (b) 200 to 1600 volts (c) 2000 to 3000 volts (d) more than 10000 volts Ans:b
197. Dielectric constant for mica is nearly (a) 200 (b) 100 (c) 3 to 8 (d) 1 to 2 Ans: c
198. The value of dielectric constant for vacuum is taken as (a) zero (b) 1 (c) 4 (d) 10 Ans: b
199. Which of the following capacitors is marked for polarity ?
(a) Air (b) Paper (c) Mica (d) Electrolytic Ans: d
200. Which of the following capacitors can be used for temperature compensation ?
(a) Air capacitor (b) Ceramic capacitor (c) Paper capacitor (d) None of the above Ans: b
201. Which of the following statements is incorrect ?
(a) The thinner the dielectric, the more the capacitance and the lower the voltage breakdown rating for a capacitor . (b) A six dot mica capacitor colour coded white, green, black, red and yellow has the capacitance value of 500 pF (c) Capacitors in series provide less capacitance but a higher voltage breakdown rating for the combination (d) A capacitor can store charge because it has a dielectric between two conductors Ans: b
202. Paper capacitors usually have a tolerance of (a) ± 5% (b) ± 10% (c) ± 15% (d) ± 20% Ans: b 203. For closer tolerances which of the following capacitors is usually preferred ?
(a) Paper capacitor (b) Mica capacitor (c) Ceramic disc capacitor (d) None of the above Ans: b
204. The electrostatic force between two charges of one coulomb each and placed at a distance of 0.5 m will be (a) 36 x 10fa (b) 36 x 107 N (c) 36 x 108 N (d) 36 x 109 N Ans: d
205. The units of volume charge density are
(a) Coulomb/metre (b) Coulomb/metre (c) Coulomb/metre (d) Coulomb/metre Ans: c
206. "The surface integral of the normal component of the electric displacement D over any closed surface equals the charge enclosed by the surface". The above statement is associated with
(a) Gauss's law (b) Kirchhoff s law (c) 's law (d) Lenz's law Ans: a
207. Dielectric strength of mica is
(a) 10 to 20 kV/mm (6) 30 to 50 kV/mm (c) 50 to 200 kV/mm (d) 300 to 500 kV/mm Ans: c
208. The dielectric constant (relative permittivity) of glass is given by
(a) 0.1 to 0.4 (b) 0.5 to 1.0(c) 2.0 to 4.0 (d) 5 to 100 Ans: d
209 capacitors are mainly used for radio frequency tuning.
(a) Paper (b) Air (c) Mica (d) Electrolytic Ans: b
210. capacitors can be used only for D.C. (a) Air (b) Paper (c) Mica (d) Electrolytic Ans: d
211. capacitors are used in transistor circuits. (a) Ceramic (b) Paper (c) Air (d) Electrolytic Ans: a 212. capacitors are used for audio frequency and radio frequency coupling and tuning.
(a) Air (b) Mica (c) Plastic film (d) Ceramic Ans: b
213. The inverse of capacitance is called
(a) reluctance (b) conductance (c) susceptance (d) elastance Ans: d
214. When the dielectric is homogeneous,the potential gradient is
(a) uniform (b) non-uniform (c) zero (d) any of the above Ans: a
215. The potential gradient across the material of low permittivity is than across the material of high permittivity. (a) smaller (b) greater (c) both (a) and (b) (d) none of the above Ans: b
216. field is associated with the capacitor.
(a) Electric (b) Magnetic (c) Both (a) and (b) (d) None of the above Ans: a
217. A capacitor having capacitance of 5 uF is charged to a potential difference of 10,000 V. The energy stored in the capacitor is (a) 50 joules (b) 150 joules (c) 200 joules (d) 250 joules Ans: d
218. A single core cable used on 33000 V has conductor diameter 10 mm and the internal diameter of sheath 25 mm. The maximum electrostatic stress in the cable is
(a) 62 x 105 V/m (b) 72 x 105 V/m (c) 82 x 105 V/m (d) 92 x 105 V/m Ans: b
219. Two infinite parallel plates 10 mm apart have maintained between them a potential difference of 100 V. The acceleration of an electron placed between them is
(a) 0.56 x 1015 m/s2 (b) 1.5 x 1015 m/s2 (c) 1.6 x 1015 m/s2 (d) 1.76 x 1015 m/s2 Ans: d
220. The total deficiency or excess of electrons in a body is known as
(a) current (b) voltage (c) potential gradient (d) charge Ans: d
221. The relative permittivity has the following units (a) F/m (b) m/F (c) Wb/m (d) no units Ans: c 222. The phenomenon of an uncharged body getting charged merely by the nearness of a charged body is known as (a) pholoelectric effect (b) chemical effect (c) magnetic effect (d) induction Ans: d 223. A unit tube of flux is known as tube
(a) Newton (b) Faraday (c) Michale (d) None of the above Ans: b
224. The number of Faraday tubes of flux passing through a surface in an electric field is called
(a) electric flux (6) electric flux density (c) magnetic flux density (d) electric charge density Ans: a 225. The unit of electric intensity is (a) N/C2 (b) Wb/m2 (c) N/C (d) N2/C Ans:c
226. The value of E within the field due to a point charge can be found with the help of
(a) Faraday's laws (b) Kirchhoff s laws (c) Coulomb's laws (d) none of the above Ans: c
227. at a point may be defined as equal to the lines of force passing normally through a unit cross section at that point.
(a) Electric intensity (6) Magnetic flux density (c) Electric flux (d) None of the above Ans: a
228. Electric intensity at any point in an electric field is equal to the at that point.
(a) electric flux (b) magnetic flux density (c) potential gradient (d) none of the above Ans: c
229. Electric displacement is a quantity.
(a) scalar (b) vector (c) both of the above (d) none of the above Ans: b
230. at a point is equal to the negative potential gradient at that point.
(a) Electric intensity (6) Electric flux (c) Magnetic flux (d) Magnetic flux density Ans: a
231. The unit of dielectric strength is given by (a) V/m (b) V2/m (c) m/V (d) m/V2 Ans: a
232. Dielectric strength with increasing thickness
(a) increases (b) decreases (c) remains unaltered (d) none of the above Ans: b
233. The property of a capacitor to store electricity is called its
(a) capacitance (b) charge (c) energy (d) none of the above Ans: a
234. is that property of a capacitor which delays any change of voltage across it.
(a) Inductance (b) Capacitance (c) Potential gradient (d) None of the above Ans: b
235. A capacitance of 100 pF is connected in series with a resistance of 8000 ohm. The time constant of the circuit is (a) 0.2 s (b) 0.4 s (c) 0.6 s (d) 0.8 s Ans: d
236. In a cable capacitor, voltage gradient is maximum at the surface of the
(a) earth (b) conduction (c) sheath (d) insulator Ans: b
237. The time constant of an R-C circuit is defined as the time during which capacitor charging voltage actually rises to _ percent of its value.
(a) 37, initial (b) 63.2, initial (c) 63.2, final (d) 37, final Ans: c
238. The time constant and R-C circuit may also be defined as the time during which the charging current falls to percent of its initial maximum value, (a) 37 (b) 42 (c) 63 (d) 73 Ans: a
239. The capacitance of a capacitor is influenced by
(a) plate area (b) plate separation (c) nature of dielectric (d) none of the above (e) all of the above Ans:e
240. A capacitor consists of two (a) ceramic plates and one mica disc (b) insulators separated by a dielectric (c) silver-coated insulators (d) conductors separated by an insulator Ans: d
241. Permittivity is expressed in
(a) Farad/sq-m (b) Farad/metre (c) Weber/metre (d) Weber/sq-m Ans: b
242. Dielectric strength of a material depends on
(a) moisture content (b) temperature (c) thickness (d) all of the above (e) none of the above Ans: d
243. What will happen to an insulating medium if voltage more than the breakdown voltage is applied on it ?
(a) It will become magnetic (b) It will melt (c) It will get punctured or cracked (d) Its molecular structure will get changed Ans: c
244. Which medium has the least dielectric strength ?
(a) Paraffin wax (b) Quartz (c) Glass (d) Air Ans: d
245. 1 volt/metre is same as
(a) 1 metre/coulomb(6) 1 newton metre(c) 1 newton/metre(d) 1 joule/coulomb Ans: c
246. One volt is the same as
(a) one joule/coulomb (b) one coulomb/joule (c) one coulomb (d) one joule Ans: a
247. The capacitance between two plates increases with
(a) shorter plate area and higher applied voltage (6) shorter plate area and shorter distance between them (c) larger plate area, longer distance between plates and higher,applied voltage (d) larger plate area and shorter distance between plates Ans: d
248. The capacitance C is charged through a resistance R. The time constant of the charging circuit is given by (a) CIR (b) 1/RC (c) RC (d) RIC Ans: c
249. The bridge used for the measurement of the value of the capacitance is
(a) Wien's bridge (b) Wheatstone bridge (c) Schering bridge (d) Hay's bridge Ans: c
250. If an ohmmeter reading immediately goes practically to zero and stays there, capacitor is
(a) charged (b) short-circuited (c) lossy (d) satisfactory Ans: b
251. Out of the following capacitors of identical rating which one will have the smallest dimensions ? (a) Aluminium foil capacitor (b) Mica capacitor (c) Ceramic capacitor (d) Paper capacitor Ans: c
252. An uncharged conductor is placed near a charged conductor, then (a) the uncharged conductor gets charged by conduction (6) the uncharged conductor gets charged by induction and then attracted towards the charging body (c) the uncharged conductor is attracted first and then charged by induction (d) it remains as such Ans: b
253. The presence of an uncharged conductor near a charged one increases the (a) charge of the charged conductor (6) capacity of the charged conductor (c) potential of the charged conductor (d) all of the above Ans:b
254.Paper condenser is (a) always polarised (6) usually of fixed value (c) electrolytic condenser (d) a variable condenser Ans: b
255. Mica capacitors are characterised by all of thte following except
(a) stable operation (b) accurate value (c) low leakage reactance (d) low losses Ans: c
256. A potential of 400 V is applied to a capacitor, the plates of which are 4 mm apart. The strength of electric field is (a) 100 kV/m (b) 10 kV/m (c) 5 kV/m (d) 2 kV/m Ans: a 257. For a good 0.05 uF capacitor ohmmeter reading should
(a) show low resistance momentarily and back off to a very high resistance (6) show high resistance momentarily and then a very low resistance (c) go quickly to 50 ohm approximately and remain there (d) not move at all Ans: a
258. The ohmmeter reading for a short circuited capacitor is
(a) infinity (b) few kilo ohms (c) few megaahms (d) zero Ans: d
259. Which of the following statements is correct ?
(a) Mica capacitors are available in capacitance values of 5 to 20 \iF (b) Air capapitors have a black band to indicate the outside foil (c) Electrolytic capacitors must be connected in correct polarity (d) Ceramic capacitors must be connected in correct polarity Ans: c
260. Which of the following capacitors preferred for high frequency circuits ?
(a) Air capacitor (b) Electrolytic capacitor (c) Mica capacitor (d) none of the above Ans: c
261. An electrolytic capacitor is generally made to provide (a) low capacitance (b) fixed capacitance (c) variable capacitance (d) large value of capacitance Ans: d
262. In order to remove static electricity from machinery
(a) construct insulated cabins (b) insulate the machinery (c) ground the framework (d) humidify the surroundings Ans: c
263. If a third equal and similar charge is placed between two equal and similar charges, then this third charge will (a) move out of the field of influence of the two charges (b) remain in stable equilibrium (c) not be in equilibrium (d) be in unstable equilibrium Ans: b
264. A region around a stationary electric charge has (a) an electric field (b) a magnetic field (c) both (a) and (b) (d) none of the above (c) reduces to zero (d) remain unchanged Ans: a
265. The minimum value of potential gradient in a cable occurs in
(a) insulation (b) conductor (c) outer sheath (d) uniformly all over Ans: a
266. Dielectric strength of medium (a) increases with rise in temperature (b) increases with moisture content (c) is same for all insulating materials (d) none of the above Ans: d
267. Acharge which when placed in vacuum from an equal and similar charge repels with a force of 9 x 10 N, is known as (a) milli-coulomb (b) micro-coulomb (c) pico-coulomb (d) coulomb Ans: b
268. Dielectric strength of a medium is usually expressed in
(a) J/mm (b) C/m2 (c) kV/mm (d) N/mm Ans: c
269. A positive and a negative charge are initially 50 mm apart. When they are moved close together so that they are now only 10 mm apart, the force between them will be (a) 5 times smaller than before (b) 5 times greater than before (c) 10 times greater than before (d) 25 times larger than before Ans: d
270. Which is the most superior dielectric out of the following ?
(a) Air (b) Glass (c) Bakelite (d) Paper Ans: c
271. When a dielectric is placed in an electric field the field strength
(a) decreases (b) increases (c) reduces to zero (d) remain unchanged Ans: a
272. To prevent the generation of static charges on rubber or flat leather
(a) surface is moistened (b) conductive dressing is done (c) oil compound dressing is done (d) talcum powder is sprayed on the surface Ans: b
273. Which of the following capacitor is preferred in case of single phase motor ?
(a) Mica capacitor (b) Paper capacitor (c) Electrolytic capacitor (d) Ceramic capacitor Ans: c
274. A capacitance is a circuit component that opposes the change in circuit (a) current (b) voltage (c) impedance (d) none of the above Ans: a
275. A condenser suitable for D.C. only is
(a) metallic plate variable gang condenser (b) metallic paper capacitor (c) oil impregrated paper condenser (d) poled aluminium electrolytic condenser Ans: d
276. In a capacitor, the electric charge is stored in
(a) metal plates (b) dielectric (c) dielectric as well as metal plates (d) none of the above Ans: b
277. An air gap is usually inserted in magnetic circuits to
(a) increase m.m.f. (b) increase the flux (c) prevent saturation (d) none of the above Ans: c
278. The relative permeability of a ferromagnetic material is (a) less than one (b) more than one (c) more than 10 (d) more than 100 or 1000 Ans: d
279. The unit of magnetic flux is (a) henry (b) weber (c) ampereturn/weber (d) ampere/metre Ans: b 280. Permeability in a magnetic circuit corresponds to in an electric circuit.
(a) resistance (b) resistivity (c) conductivity (d) conductance Ans: c
281. Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it (a) lowers their power efficiency (b) increases their cost of (c) leads to their increased weight (d) produces fringing Ans: a
282. Relative permeability of vacuum is (a) 1 (b) 1 H/m (c) 1/4JI (d) 4n x 10-' H/m Ans: a
283. Permanent magnets are normally made of
(a) alnico alloys (b) aluminium (c) cast iron (d) wrought iron Ans: a
284. Energy stored by a coil is doubled when its current is increased by percent.
(a) 25(b) 50 (c)41.4 (d) 100 Ans: c
285. Those magnetic materials are best suited for making armature and transformer cores which have permeability and hystersis loss. (a) high, high (b) low, high (c) high, low (d) low, low Ans: c
286. The rate of rise of current through an inductive coil is maximum
(a) at 63.2% of its maximum steady value (b) at the start of the current flow (c) after one time constant (d) near the final maximum value of current Ans: b
287. When both the inductance and resistance of a coil are doubled the value of
(a) time constant remains unchanged (b) initial rate of rise of current is doubled (c) final steady current is doubled (d) time constant is halved Ans: a
288. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is Vs (a) 50 (b) 20 (c) 0.05 (d) 500 Ans: b
289. A material for good magnetic memory
(a) low hysteresis loss (b) high permeability (c) low retentivity (d) high retentivity Ans: d
290. Conductivity is analogous to (a) retentivity (b) resistivity (c) permeability (d) inductance Ans: c 291. In a magnetic material hysteresis loss takes place primarily due to
(a) rapid reversals of its magnetization (b) flux density lagging behind magnetising force (c) molecular friction (d) it high retentivity Ans: d
292. Those materials are well suited for making permanent magnets which have retentivity and coercivity. (a) low, high (b) high, high (c) high, low (d) low, low Ans: b
293. If the area of hysteresis loop of a material is , the hysteresis loss in this material will be
(a) zero (b) small (c) large (d) none of the above Ans: c
294. Hard steel is suitable for making permanent magnets because
(a) it has good residual magnetism (b) its hysteresis loop has large area (c) its mechanical strength is high (d) its mechanical strength is low Ans: a
295. Silicon steel is used in electrical machines because it has
(a) low co-ercivity (b) low retentivity (c) low hysteresis loss (d) high co-ercivity Ans: c
296. Conductance is analogous to (a) permeance (b) reluctance (c) flux (d) inductance Ans: a
297. The property of a material which opposes the creation of magnetic flux in it is known as
(a) reluctivity (b) magnetomotive force (c) permeance (d) reluctance Ans: d
298. The unit of retentivity is (a) weber (b) weber/sq. m (c) ampere turn/metre (d) ampere turn Ans: b 299.Reciprocal of reluctance is (a) reluctivity (b) permeance (c) permeability (d) susceptibility Ans:b
300.While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit ?
(a) E.m.f. (b) Current (c) Current density (d) Conductivity Ans: b
301. The unit of reluctance is (a) metre/henry (b) henry/metre (c) henry (d) 1/henry Ans: d
302. A ferrite core has less eddy current loss than an iron core because
(a) ferrites have high resistance (b) ferrites are magnetic (c) ferrites have low permeability (d) ferrites have high hysteresis Ans: d
303. Hysteresis loss least depends on (a) volume of material (b) frequency (c) steinmetz co-efficient of material(d) ambient temperature Ans: d
304. Laminated cores, in electrical machines, are used to reduce
(a) copper loss (b) eddy current loss (c) hysteresis loss (d) all of the above Ans: b
305. "The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity".The above statement is associated with (a) Newton's law (b) Faraday's law of electromagnetic (c) Faraday's law of electrolysis (d) Gauss's law Ans: c
306. The charge required to liberate one gram equivalent of any substance is known as constant
(a) time (b) Faraday's (c) Boltzman Ans: b
307. During the charging of a lead-acid cell (a) its voltage (b) it gives out energy (c) its cathode becomes dark chocolate brown in colour (d) specific gravity of H2SO4 decreases Ans: a
308. The capacity of a lead-acid cell does not depend on its
(a) temperature (b) rate of charge (c) rate of discharge (d) quantity of active material Ans: b
309. During charging the specific gravity of the electrolyte of a lead-acid battery
(a) increases (b) decreases (c) remains the same (d) becomes zero Ans: a
310. The active materials on the positive and negative plates of a fully charged lead-acid battery are (a) lead and lead peroxide (b) lead sulphate and lead (c) lead peroxide and lead (d) none of the above Ans: c
310. When a lead-acid battery is in fully charged condition, the colour of its positive plate is (a) dark grey (b) brown (c) dark brown (d) none of above Ans: c
311. The active materials of a nickel-iron battery are (a) nickel hydroxide (6) powdered iron and its oxide (c) 21% solution of KOH (d) all of the above Ans: d
312. The ratio of ampere-hour efficiency to watt-hour efficiency of a lead-acid cell is (a) just one (b) always greater than one (c) always less than one (d) none of the above. Ans: b
313. The best indication about the state of charge on a lead-acid battery is given by (a) output voltage (b) temperature of electrolyte (c) specific gravity of electrolyte (d) none of the above Ans: c
314. The storage battery generally used in electric power station is
(a) nickel-cadmium battery (b) zinc-carbon battery (c) lead-acid battery (d) none of the above Ans: c
315. The output voltage of a charger is (a) less than the battery voltage (b) higher than the battery voltage (c) the same as the battery voltage (d) none of the above Ans: b
316. Cells are connected in series in order to (a) increase the voltage rating (6) increase the current rating (c) increase the life of the cells (d) none of the above Ans: a
317. Five 2 V cells are connected in parallel.The output voltage is
(a) 1 V (6) 1.5 V (c) 1.75 V (d) 2 V Ans: d
318. The capacity of a battery is expressed in terms of
(a) current rating (b) voltage rating (e) ampere-hour rating (d) none of the above Ans: c
319. Duringthe charging and discharging of a nickel-iron cell
(a) corrosive fumes are produced (b) water is neither formed nor absorbed (c) nickel hydroxide remains unsplit (d) its e.m.f. remains constant Ans: b
320. As compared to constant-current system, the constant-voltage system of charging a lead acid cell has the advantage of
(a) reducing time of charging (b) increasing cell capacity (c) both (a) and (b) (d) avoiding excessive gassing Ans: c
321. A dead storage battery can be revived by
(a) adding (6) adding so-called battery restorer (c) a dose of H2SO4 (d) none of the above Ans: d
322. As compared to a lead-acid cell, the efficiency of a nickel-iron cell is less due to its
(a) compactness (b) lower e.m.f. (c) small quantity of electrolyte used (d) higher internal resistance Ans: d
323. Trickle charging of a storage battery helps to
(a) maintain proper electrolyte level (b) increase its reserve capacity (c) prevent sulphation (d) keep it fresh and fully charged Ans: d
324. Those substances of the cell which take active part in chemical combination and hence produce electricity during charging or discharging are known as materials.
(a) passive (b) active (c) redundant (d) inert Ans: b
325. In a lead-acid cell dilute sulphuric acid (electrolyte) approximately comprises the following
(a) one part H2O, three parts H2SO4 (b) two parts H2O, two parts H2SO4 (c) three parts H2O, one part H2SO4 (d) all H2S04 Ans: c
326. It is noticed that durmg charging (a) there is a rise in voltage (6) energy is absorbed by the cell (c) specific gravity of H2SO4 is increased (d) the anode becomes chocolate brown in colour (PbCfe) and cathode becomes grey metallic lead (Pb) (e) all of the above Ans: e
327. It is noticed that during discharging the following does not happen (a) both anode and cathode become PbS04 (b) specific gravity of H2SO4 decreases (c) voltage of the cell decreases (d) the cell absorbs energy Ans: d
328. The ampere-hour efficiency of a leadacid cell is normally between (a) 20 to 30% (b) 40 to 50% (c) 60 to 70% (d) 90 to 95% Ans: d 329. The watt-hour efficiency of a lead-acid cell varies between (a) 25 to 35% (b) 40 to 60% (c) 70 to 80% (d) 90 to 95% Ans: c
330. The capacity of a lead-acid cell is measured in
(a) amperes (b) ampere-hours (c) watts (d) watt-hours Ans: b
331. The capacity of a lead-acid cell depends on (a) rate of discharge (b) temperature (c) density of electrolyte (d) quantity of active materials (e) all above Ans: e
332. When the lead-acid cell is fully charged, the electrolyte assumes _ appearance
(a) dull (b) reddish (c) bright (d) milky Ans: d
333. The e.m.f. of an Edison cell, when fully charged, is nearly
(a) 1.4 V (b) 1 V (c) 0.9 V (d) 0.8 V Ans: a
334. The internal resistance of an alkali cell is nearly times that of the lead- acid cell. (a) two (b) three (c) four (d) five Ans: d
335. The average charging voltage for alkali cell is about (a) 1 V (b) 1.2 V (c) 1.7 V (d) 2.1 V Ans: c 336. On the average the ampere-hour efficiency of an Edison cell is about (a) 40% (b) 60% (c) 70% (d) 80% Ans: d
337. The active material of the positive plates of silver-zinc batteries is (a) silver oxide (b) lead oxide (c) lead (d) zinc powder Ans: a
338.Lead-acid cell has a life of nearly charges and discharges
(a) 500 (b) 700 (c) 1000 (d) 1250 Ans: d
339. Life of the Edison cell is at least (a) five years (b) seven years (c) eight years (d) ten years Ans:a 340. The internal resistance of a lead-acid cell is that of Edison cell
(a) less than (b) more than (c) equal to (d) none of the above Ans: a
341. Electrolyte used in an Edison cell is (a) NaOH (b) KOH (c) HC1 (d) HN03 Ans: b
342. Electrolyte used in a lead-acid cell is
(a) NaOH (b) onlyH2S04 (c) only water (d) dilute H2SO4 Ans: d
343. Negative plate of an Edison cell is made of (a) copper (b) lead (c) iron (d) silver oxide Ans: c 344. The open circuit voltage of any storage cell depends wholly upon (a) its chemical constituents (b) on the strength of its electrolyte (c) its temperature (d) all above Ans: d
345. The specific gravity of electrolyte is measured by
(a) manometer (6) a mechanical gauge (c) hydrometer (d) psychrometer Ans: c
346. When the specific gravity of the electrolyte of a lead-acid cell is reduced to 1.1 to 1.15 the cell is in (a) charged state (b) discharged state (c) both (a) and (b) (d) active state Ans: b
347. In system the charging current is intermittently controlled at either a maximum or minimum value (a) two rate charge control (b) trickle charge (c) floating charge (d) an equalizing charge Ans: a 348. Over charging (a) produces excessive gassing (b) loosens the active material (e) increases the temperature resulting in buckling of plates (d) all above Ans: d
349. Undercharging (a) reduces specific gravity of the electrolyte (b) increases specific gravity of the electrolyte (c) produces excessive gassing (d) increases the temperature Ans: a
350. Internal short circuits are caused by (a) breakdown of one or more separators (b) excess accumulation of sediment at the bottom of the cell (c) both (a) and (b) (d) none of the above Ans: c 351. The effect of sulphation is that the internal resistance
(a) increases (b) decreases(c) remains same (d) none of the above Ans: a
352. Excessive formation of lead sulphate on the surface of the plates happens because of
(a) allowing a battery to stand in discharged condition for a long time (b) topping up with electrolyte (c) persistent undercharging (d) low level of electrolyte (e) all above Ans: e
353. The substances which combine together to store electrical energy during the charge are called materials (a) active (b) passive (c) inert (d) dielectric Ans: a
354. In a lead-acid cell, lead is called as (a) positive active material (b) negative active material (c) passive material (d) none of the above Ans: b
355. The lead-acid cell should never be discharged beyond
(a) 1.8 V (b) 1.9 V (c) 2 V (d) 2.1 V Ans: a
356. On overcharging a battery
(a) it will bring about chemical change in active materials (b) it will increase the capacity of the battery (c) it will raise the specific gravity of the electrolyte (d) none of the above will occur Ans: d
357. Each cell has a vent cap (a) to allow gases out when the cell is on charge (b) to add water to the cell if needed (c) to check the level of electrolyte (d) to do all above functions Ans: d
358. Following will occur if level of electrolyte falls below plates (a) capacity of the cell is reduced (b) life of the cell is reduced (c) open plates are converted to lead sulphate (d) all above Ans: d
359. In constant voltage charging method, the charging current from discharged to fully charged condition (a) decreases (b) increases (c) remains constant (d) none of the above Ans: a
360. 48 ampere-hour capacity would deliver a current of (a) 48 amperes for 1 hour (b) 24 amperes for 2 hours (c) 8 amperes for 6 hours (d) 6 amperes for 8 hours Ans: d
361. In constant-current charging method, the supply voltage from discharged to fully charged condition (a) decreases (b) increases (c) remains constant (d) none of the above Ans: b
362. Battery charging equipment is generally installed
(a) in well ventilated location (b) in clean and place (c) as near as practical to the battery being charged (d) in location having all above features Ans: d
363. Following will happen if the specific gravity of electrolyte becomes more than 1.23. (a) Loss of capacity (b) Loss of life (c) Corrosion of the grids of the plate (d) All above Ans: d
364.Batteries are charged by
(a) rectifiers (b) engine generator sets (c) motor generator sets(d)any one of the above methods Ans:d
365. Cell short circuit results in (a) low sp. gravity electrolyte (b) abnormal high temperature (c) reduced gassing on charge (d) all above Ans: d
366. Internal resistance of a cell is reduced by
(a) using vent plug to permit gas formed during discharge (b) increasing the plate area (c) putting plates very close together (d) all above methods Ans: d
367. Capacity of dry cells is
(a) more when it is supplying current for intermittent periods (b) more when it is supplying current for continuous periods (c) unaffected by the type of discharge (d) none of the above Ans: a
368. Battery container should be acid resistance, therefore it is made up of
(a) glass (b) plastic (c) wood (d) all above Ans: d
369. Sulphated cells are indicated by (a) the loss of capacity of the cell (6) the decrease of the specific gravity (c) the low voltage of the cell on discharge (d) all above conditions Ans: d
370. In a lead-acid cell, if the specific gravity of sulphuric acid is 1.8, it will require following ratio of acid towater to get mixture of specific gravity of 1.3
(a) 6 parts of acid to 4 parts of water (b) 4 parts of acid to 4 parts of water (c) 4 parts of acid to 6 parts of water (d) 4 parts of acid to 8 parts of water Ans: c
371. Local action in a battery is indicated by
(a) excessive gassing under load conditions (b) excessive drop in the specific gravity of electrolyte even when the cell is on open circuit (c) both (a) and (b) (d) none of the above Ans: d
372. Following will happen if battery charging rate is too high
(a) excessive gassing will occur (b) temperature rise will occur (c) bulging and buckling of plates will occur (d) all above will occur Ans: d
373. Internal resistance of a cell is due to (a) resistance of electrolyte (b) electrode resistance (c) surface contact resistance between electrode and electrolyte (d) all above Ans: d
374. If a battery is wrongly connected on charge following will happen (a) current delivered by the battery will be high (b) current drawing will be nil (c) current drawing will be very small (d) current drawing will be very high Ans: d
375. In order that a hydrometer may float vertically in electrolyte its C.G. should be (a) lowered (b) raised (c) undisturbed (d) displaced sidewaysAns: a
376. If a lead-acid cell is discharged below 1.8 V the following will happen.
(a) Capacity of cell will reduce (b) Sulphation of plates will occur (c) Internal resistance will increase (d) All above will occur Ans: d
377. Life of the batteries is in the following ascending order. (a) Lead-acid cell, Edison cell, Nickel cadmium cell (b) Lead-acid cell, Nickel-cadmium cell, Edison cell (c) Edison cell, Nickel-cadmium cell, lead-acid cell (d) Nickel-cadmium cell, Edison cell, lead-acid cell Ans: a
378. Persons preparing electrolyte should wear (a) goggles or other face shield (b) rubber (c) rubber boots and gloves (d) all above safety devices Ans: d
379. Excessive charging a battery tends to (a) produce gassing (b) increase the internal resistance of the battery (c) to corrode the positive plates into lead peroxide thereby weakening them physically (d) bring about all above changes Ans: d
380. Shelf life of a small dry cell is (a) equal to that of large dry cell (6) less than that of large dry cell (c) more than that of large dry cell (d) none of the above Ans: b
381. The current flow through electrolyte is due to the movement of
(a) ions (b) holes (c) electrons (d) none of the above Ans: a
382. Level of electrolyte in a cell should be the level of plates
(a) below (b) equal to (c) above (d) none of the above Ans: c
383. During discharge, the active material of both the positive and negative plates is changed to
(a) Pb (b) Pb02 (c) PbO (d) PbS04 Ans: d
384. of electrolytelndicates the state of charge of the battery
(a) colour (b) mass (c) viscosity (d) specific gravity Ans: d
385. The following indicate that battery on charge has attained full charge
(a) colour of electrode (b) gassing (c) specific gravity (d) all above Ans: d
386. Dry cell is modification of
(a) Deniell cell (b) Leclanche cell (e) Lead-acid cell (d) Edison cell Ans: b
387. Capacity of a battery.is expressed in
(a) Ah (b) Vh (c) Wh (d) kWh Ans: a
388. In alkaline cell the electrolyte is
(a) dilute sulphuric acid (b) concentrated sulphuric acid (c) NaOH (d) KOH Ans: d
389. Self charge of a Ni-Fe cell is Edison cell.
(a) equal to (b) less than (c) more than (d) much more than Ans: b
390. Ampere hour capacity of an industrial battery is based on hours discharge rate.
(a) 8 (b) 12 (c) 16 (d) 24 Ans: a
391. The body of Edison cell is made of
(a) bakelite (b) rubber (c) nickel plated steel (d) aluminium Ans: c
392. Specific gravity of electrolyte in Edison cell is (a) 0.8 (b) 0.95 (c) 1.1 (d) 1.21 Ans: d
393. All the electrical connections between the battery and vehicle should be by
(a) thin aluminium wires (b) thin copper wires (c) rigid cables (d) flexible cables Ans: d
394. A battery of 6 cells will show a drop of volts from fully charged state to fully discharged state. (a) 1.0 (b) 1.5 (c) 2.4 (d) 2.9 Ans: c
395. During the idle period of the battery, strong electrolyte tends to change the active material of the cell into (a) Pb02 (6) PbSC-4 (c) PbO (d) Pb Ans: b
396. Chargmg of sulphated battery produces heat. (a) no (b) very little (c) less (d) more Ans: d
397. Hydrogen evolved during charging produces explosive mixture when it is more than
(a) 2% (b) 4% (c) 6% (d) 8% Ans: d
398. Weston standard cell at 20°C has voltage of volts. (a) 0.8 (b) 0.9 (c) 1.0187 (d) 1.5 Ans: c
399. Extent of corrosion in the underground metal work depends upon
(a) amount of moisture (b) type of metals (c) type of soil chemicals (d) all above factors Ans: d
400. Mercury cell has which of the following characteristics ?
(a) Flat discharge current-voltage curve (6) High power to weight ratio (c) Comparatively longer shelf life under adverse conditions of high temperature and humidity (d) All of the above Ans: d
401. Charging a sulphated battery at high rate results in
(a) boiling of electrolyte due to gassing (b) warping of plates (c) damage to separators, cell caps covers and battery case due to excessive temperature (d) all above Ans: d
402. Short circuiting of a cell may be caused
(a) buckling of plates (b) faulty separators (c) lead particles forming circuit between positive and negative plates (d) excessive accumulation of sediment (e) any one of above Ans: e
403. In a battery cover is placed over the element and sealed to the top of the battery container. This is done (a) to reduce evaporation of water from electrolyte (b) to exclude dirt and foreign matter from the electrolyte (c) to discharge both of the above functions (d) to discharge none of the above functions Ans: c
404. For a cell to work, which of the following condition(s) become necessary ?
(a) Two electrodes of different meta's should be inserted in the electrolyte, not touching each other (b) Electrolyte must chemically react with one of the electrodes (c) Electrolyte liquid or paste should be conducting (d) All above three conditions are necessary Ans: d
405. Which of the following primary cells has the lowest voltage ?
(a) Lithium (b) Zinc-chloride (c) Mercury (d) Carbon-zinc Ans: c
406. Which of the following primary cells has the highest voltage ? (a) Manganese-alkaline (6) Carbon-zinc (c) Lithium (d) Mercury Ans: c
407. While preparing electrolyte for a lead-acid battery (a) water is poured into acid (b) acid is poured into water (c) anyone of the two can be added to other chemical Ans: b
408. Which of the following battery is used for air-craft ?
(a) Lead-acid battery (b) Nickel-iron battery (c) Dry cell battery (d) Silver oxide battery Ans: b
409. Which of the following cell has a. reversible chemical reaction ?
(a) Lead-acid (b) Mercury oxide (c) Carbon-zinc (d) Silver-oxide Ans: a
410. Which of the following is incorrect ? (a) A storage cell has a reversible chemical reaction (b) A lead-acid cell can be recharged (c) A carbon-zinc cell has unlimited shelf life (d) A primary cell has an irreversible chemical reaction Ans: c
411. Which of the following has lower sp. gravity V
(a) Dilute H2S04 (6) Concentrated H2SO4 (c) Water (d) Any of the above Ans: c
412. Under normal charging rate, the charging current should be
(a) 10% of capacity (b) 20% of capacity (c) 30% of capacity (d) 40% of capacity Ans: a
413. When two batteries are connected in parallel, it should be ensured that (a) they have same e.m.f. (b) they have same make (c) they have same ampere-hour capa-city (d) they have identical internal resistance Ans: a
414. A typical output of a solar cell is (a) 0.1V (b) 0.26 V (c) 1.1 V (d) 2 V Ans: b
415. Petroleum jelly is applied to the electrical connections to the lead-acid battery (a) prevent local heating (b) prevent short-circuiting (c) reduce path resistance (d) prevent corrosion Ans: d
416. When the load resistance equals the generator resistance which of the following will be maximum ? (a) Current (b) Efficiency of the circuit (c) Power in the load resistance (d) Voltage across the load resistance Ans: c
417. The common impurity in the electrolyte of lead-acid battery is
(a) chlorine (b) dust particles (c) lead crystals (d) iron Ans: d
418. In a lead-acid battery the energy is stored in the form of
(a) charged ions (b) chemical energy (c) electrostatic energy (d) electromagnetic energy Ans: b
419. Which among the following constitutes the major load for an ?
(a) (b) Self starter (c) Parking lights (d) Spark plugs Ans: b
420. Which of the following factors adversely affects the capacity of the leadacid battery ?
(a) Temperature of surroundings (b) Specific gravity of electrolyte (c) Rate of discharge (d) All of the above Ans: d
421. Cells are connected in parallel to (a) increase the efficiency (b) increase the current capacity (c) increase the voltage output (d) increase the internal resistance Ans: b
422. A constant-voltage generator has (a) minimum efficiency (b) minimum current capacity (c) low internal resistance (d) high internal resistance Ans: c
423. The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as
(a) self-inductance (b) mutual inductance (c) series aiding inductance (d) capacitance Ans: a
424. As per Farada y's laws of electromagnetic induction, an e.m.f. is induced in a conductor whenever it (a) lies perpendicular to the magnetic flux (b) lies in a magnetic field (e) cuts magnetic flux (d) moves parallel to the direction of the magnetic field Ans: c
425. Which of the following circuit element stores energy in the electromagnetic field ?
(a) Inductance (b) Condenser (c) Variable resistor (d) Resistance Ans: a
426. The inductance of a coil will increase under all the following conditions except (a) when more length for the same number of turns is provided (6) when the number of turns of the coil increase (c) when more area for each turn is provided (d) when permeability of the core Ans: a
427. Higher the self-inductance of a coil, (a) lesser its weber-turns (b) lower the e.m.f. induced (c) greater the flux produced by it (d) longer the delay in establishing steady current through it Ans: d 428. In an iron cored coil the iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will
(a) increase (b) decrease (c) remain the same (d) initially increase and then decrease Ans: b
429. An open coil has (a) zero resistance and inductance (b) infinite resistance and zero inductance (c) infinite resistance and normal inductance (d) zero resistance and high inductance Ans: b
430. Both the number of turns and the core length of an inductive coil are doubled. Its self-inductance will be (a) unaffected (b) doubled (c) halved (d) quadrupled Ans: b
431. If current in a conductor increases then according to Lenz's law self-induced voltage will
(a) aid the increasing current (b) tend to decrease the amount of cur-rent (c) produce current opposite to the in-creasing current (d) aid the applied voltage Ans: c
432. The direction of incViced e.m.f. can be found by (a) Laplace's law (b) Lenz's law (c) Fleming's right hand rule (d) Kirchhoff s voltage law Ans: b
433. Air-core coils are practically free from
(a) hysteresis losses (b) eddy current losses (c) both (a) and (b) (d) none of the above Ans: c
434. The magnitude of the induced e.m.f. in a conductor depends on the
(a) flux density of the magnetic field (b) amount of flux cut (c) amount of flux linkages (d) rate of change of flux-linkages Ans: d
435. Mutually inductance between two magnetically-coupled coils depends on
(a) permeability of the core (b) the number of their turns (c) cross-sectional area of their com-mon core (d) all of the above Ans: d
436. A laminated iron core has reduced eddy-current losses because (a) more wire can be used with less D.C. resistance in coil (b) the laminations are insulated from each other (c) the magnetic flux is concentrated in the air gap of the core (d) the laminations are stacked vertf-cally Ans: b
437. The law that the induced e.m.f. and current always oppose the cause producing them is due to (a) Faraday (b) Lenz (c) Newton (d) Coulomb Ans: b
438. Which of the following is not a unit of inductance ?
(a) Henry (b) Coulomb/volt ampere (c) Volt second per ampere (d) All of the above Ans: b
439. In case of an inductance, current is proportional to (a) voltage across the inductance (b) magnetic field (c) both (a) and (b) (d) neither (a) nor (b) Ans: b
440. Which of the following circuit elements will oppose the change in circuit current ?
(a) Capacitance (b) Inductance (c) Resistance (d) All of the above Ans: b
441. For a purely inductive circuit which of the following is true ?
(a) Apparent power is zero (b) Relative power is.zero (c) Actual power of the circuit is zero (d) Any capacitance even if present in the circuit will not be charged Ans: c
442. Which of the following is unit of inductance ?
(a) Ohm (b) Henry (c) Ampere turns (d) Webers/metre Ans: b
443. An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be (a) 64 A/s (b) 32 A/s (c) 16 A/s (d) 4 A/s Ans: d
444. The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. If the core length is doubled, all other quantities, remaining the same, the in ductance will be
(a) 3 mH (b) 12 mH (c) 24mH (d)48mH Ans: a
445. The self inductances of two coils are 8 mH and 18 mH. If the co-efficients of coupling is 0.5, the mutual inductance of the coils is (a) 4 mH (b) 5 mH (c) 6 mH (d) 12 mH Ans: c
446. Two coils have inductances of 8 mH and 18 mH and a co-efficient of coupling of 0.5. If the two coils are connected in series aiding, the total inductance will be
(a) 32 mH (b) 38 mH (c) 40 mH (d) 48 mH Ans: b
447. A 200 turn coil has an inductance of 12 mH. If the number of turns is increased to 400 turns, all other quantities (area, length etc.) remaining the same, the inductance will be
(a) 6 mH (b) 14 mH (c) 24 mH (d) 48 mH Ans: d
448. Two coils have self-inductances of 10 H and 2 H, the mutual inductance being zero. If the two coils are connected in series, the total inductance will be (a) 6 H (b) 8 H (c) 12 H (d) 24 H Ans: c
449. In case all the flux from the current in coil 1 links with coil 2, the co-efficient of coupling will be (a) 2.0 (b) 1.0 (c) 0.5 (d) zero Ans: b
450. A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is
(a) 50 ohms (b) 500 ohms (c) 1000 ohms (d) 5000 ohms Ans: d
451. A conductor 2 metres long moves at right angles to a magnetic field of flux density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductor will be
(a) 10 V (6) 15 V (c) 25V (d) 50V Ans: c
452. Lenz's law is a consequence of the law of conservation of (a) induced current (b) charge (c) energy (d) induced e.m.f. Ans: c
453. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly (a) 50 N (b) 120 N (c) 240 N (d) 480 N Ans: b
454. Find the force acting on a conductor 3m long carrying a current of 50 amperes at right angles to a magnetic field having a flux density of 0.67 tesla. (a) 100 N (b) 400 N (c) 600 N (d) 1000 N Ans: a 455. The co-efficient of coupling between two air core coils depends on
(a) self-inductance of two coils only (b) mutual inductance between two coils only (c) mutual inductance and self inductance of two coils (d) none of the above Ans: c
456. An average voltage of 10 V is induced in a 250 turns solenoid as a result of a change in flux which occurs in 0.5 second. The total flux change is
(a) 20 Wb (b) 2 Wb (c) 0.2 Wb (d) 0.02 Wb Ans: d
457. A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage ? (a) 0.01 s (b) 0.1 s (c) 0.5 s (d) 5 s Ans: c 458. Which of the fpllowing inductor will have the least eddy current losses ?
(a) Air core (b) Laminated iron core (c) Iron core (d) Powdered iron core Ans: a
459. A coil induces 350 mV when the current changes at the rate of 1 A/s. The value of inductance is (a) 3500 mH (b) 350 mH (c) 250 mH (d) 150 mH Ans: b
460. Two 300 uH coils in series without mutual coupling have a total inductance of
(a) 300 uH (b) 600 uH (c) 150 uH (d) 75 uH Ans: b
461. Current changing from 8 A to 12 A in one second induced 20 volts in a coil. The value of inductance is (a) 5 mH (b) 10 mH (c) 5 H (d) 10 H Ans: c
462. Which circuit element(s) will oppose the change in circuit current ?
(a) Resistance only (b) Inductance only (c) Capacitance only (d) Inductance and capacitance Ans: b
463. A crack in the magnetic path of an inductor will result in
(a) unchanged inductance (b) increased inductance (c) zero inductance (d) reduced inductance Ans: d
464. A coil is wound on iron core which carries current I. The self-induced voltage in the coil is not affected by (a) variation in coil current (b) variation in voltage to the coil (c) change of number of turns of coil (d) the resistance of magnetic path Ans: b
465. A moving magnetic field will produce the same effect as a conductor that is moving.
(a) Yes (b) No Ans:a
466. The polarity of the induced voltage can be determined by using the left-hand generator rule.
(a) Yes (b) No Ans: a
467. Increasing the field or increasing the current will decrease the force on the conductor.
(a) Yes (b) No Ans: b
468. Reversing the field or the current will reverse the force on the conductor. (a) Yes (b) No Ans: a 469 When a conductor moves in the field, so that it makes an angle 8 with the lines of flux, the force F is given as : F = Bl sin2 0. (a) Yes (b) No Ans: b
470. The self-inductance of the coil may be defined as equal to the e.m.f. induced in volts when the current in the circuit changes at the rate of unit weber turns. (a) Yes (b) No Ans: b
471. Laminations of core are generally made of
(a) case iron (b) carbon (c) silicon steel (d) stainless steel Ans: c
472. Which of the following could be lamina-proximately the thickness of lamina-tions of a D.C. machine? (a) 0.005 mm (b) 0.05 mm (c) 0.5 m (d) 5 m Ans: c
473. The armature of D.C. generator is laminated to
(a) reduce the bulk (b) provide the bulk (c) insulate the core (d) reduce eddy current loss Ans: d
474. The resistance of armature winding depends on (a) length of conductor (b) cross-sectional area of the conductor (c) number of conductors (d) all of the above Ans: d
475. The field coils of D.C. generator are usually made of
(a) mica (b) copper (c) cast iron (d) carbon Ans: b
476. The commutator segments are connected to the armature conductors by means of
(a) copper lugs (b) resistance wires (c) insulation pads Ans: a
477. In a commutator (a) copper is harder than mica (b) mica and copper are equally hard (c) mica is harder than copper (d) none of the above Ans: c
478. In D.C. generators the pole shoes are fastened to the pole core by
(a) rivets (b) counter sunk screws (c) brazing (d) welding Ans: b
479. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of
(a) motion of conductor (b) lines of force (c) either of the above (d) none of the above Ans: b
480. Fleming's right-hand rule regarding direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow and resultant force (b) magnetic flux, direction of motion and the direction of e.m.f. induced (c) magnetic field strength, induced voltage and current (d) magnetic flux, direction of force and direction of motion of conductor Ans: b
481. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards (a) direction of induced e.m.f. (b) direction of flux (c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f. (d) direction of motion of conductor, if forefinger points along the lines of flux Ans: d
482. The bearings used to support the rotor shafts are generally (a) ball bearings (b) bush bearings (c) magnetic bearmgs (d) needle bearing Ans: a
483. In D.C. generators, the cause of rapid brush wear may be
(a) severe sparking (b) rough commutator surface (c) imperfect contact (d) any of the above Ans: d
484. In lap winding, the number of brushes is always (a) double the number of poles (b) same as the number of poles (c) half the number of poles (d) two Ans: b
485. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ? (a) Lap winding (b) Wave winding (c) Either of (a) and (b) above (d) Depends on other features of design Ans: b
486. In a four-pole D.C. machine (a) all the four poles are north poles (b) alternate poles are north and south (c) all the four poles are south poles (d) two north poles follow two south poles Ans: b
487. Copper brushes in D.C. machine are used
(a) where low voltage and high currents are involved (b) where high voltage and small cur-rents are involved (c) in both of the above cases (d) in none of the above cases Ans: a
488. A separately excited generator as compared to a self-excited generator
(a) is amenable to better voltage con-trol (b) is more stable (c) has exciting current independent of load current (d) has all above features Ans: d
489. In case of D.C. machines, mechanical losses are primary function of
(a) current (b) voltage (c) speed (d) none of above Ans: c
490. Iron losses in a D.C. machine are independent of variations in
(a) speed (b) load (c) voltage (d) speed and voltage Ans: b
491. In D.C. generators, current to the external circuit from armature is given through
(a) commutator (b) solid connection (c) slip rings (d) none of above Ans: a
492. Brushes of D.C. machines are made of
(a) carbon (b) soft copper (c) hard copper (d) all of above Ans: a
493. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by (a)Blv (b)Blv2 (c)Bl2v (d)Bl2v2 Ans: a
494. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be (a) 4 (b) 8 (c) 16 (d) 32 Ans: b
495. The material for commutator brushes is generally
(a) mica (b) copper (c) cast iron (d) carbon Ans: d
496. The insulating material used between the commutator segments is normally
(a) graphite (b) paper (c) mica (d) insulating varnish Ans: c
497. In D.C. generators, the brushes on commutator remain in contact with conductors which
(a) lie under south pole (b) lie under north pole (c) lie under interpolar region (d) are farthest from the poles Ans: c
498. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be (a) demagnetisation only (b) cross magnetisation as well as magnetisation (c) crossmagnetisation as well as demagnetising (d) cross magnetisation only Ans: c
499. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising (b) demagnetising (c) magnetising (d) none of above Ans: a
500. D.C. generators are connected to the busbars or disconnected from them only under the floating condition (a) to avoid sudden loading of the primemover (b) to avoid mechanicaljerk to the shaft (c) to avoid burning of switch contacts (d) all above Ans: d
501. Eddy currents are induced in the pole shoes of a D.C. machine due to (a) oscillating magnetic field (b) pulsating magnetic flux (c) relative rotation between field and armature (d) all above Ans: c 502. In a D.C. machine, short-circuited field coil will result in (a) odour of barning insulation (b) unbalanced magnetic pull producing vibrations (c) reduction of generated voltage for which excitation has to be increased to maintain the voltage (d) all above Ans: d
503. Equilizer rings are required in case armature is
(a) wave wound (b) lap wound (c) delta wound (d) duplex wound Ans: b
504. Welding generator will have
(a) lap winding (b) wave winding (c) delta winding (d) duplex wave winding Ans: a
505. In case of D.C. machine winding, number of commutator segments is equal to
(a) number of armature coils (b) number of armature coil sides (c) number of armature conductors (d) number of armature turns Ans: a
506. For a D.C. machines laboratory following type of D.C. supply will be suitable
(a) rotary converter (b) mercury are rectifier (c) induction motor D.C. generator set (d) synchronous motor D.C. generator set Ans: c
507. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the magnetic path (b) to spread out the flux to achieve uniform flux density (c) to support the field coil (d) to discharge all the above functions Ans: d
508. In the case of lap winding resultant pitch is
(a) multiplication of front and back pitches (b) division of front pitch by back pitch (c) sum of front and back pitches (d) difference of front and back pitches Ans: d
509. A D.C. welding generator has
(a) lap winding (b) wave moving (c) duplex winding (d) any of the above Ans: a
510. Which of the following statement about D.C. generators is false ?
(a) Compensating winding in a D.C. machine helps in commutation (b) In a D. C. generator interpoles winding is connected in series with the armature winding (c) Back pitch and front pitch are both odd and approximately equal to the pole pitch (d) Equilizing bus bars are used with parallel running of D.C. shunt generators Ans: d
511. The demagnetising component of armature reaction in a D.C. generator
(a) reduces generator e.m.f. (b) increases armature speed (c) reduces interpoles flux density (d) results in sparking trouble Ans: a
512. Magnetic field in a D.C. generator is produced by
(a) electromagnets (b) permanent magnets (c) both (a) and (b) (d) none of the above Ans: a
513. The number of brushes in a commutator depends on
(a) speed of armature (b) type of winding (c) voltage (d) amount of current to be collected Ans: d 514. Compensating windings are used in D.C. generators (a) mainly to reduce the eddy currents by providing local short-circuits (b) to provide path for the circulation of cooling air (c) to neutralise the cross-magnetising effect of the armature reaction (d) none of the above Ans: c
515. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ? (a) Dummy coils (b) Commutator (c) Eye bolt (d) Equilizer rings Ans: b 516. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by (a) using conductor of annealed copper (b) using commutator with large number of segments (c) using carbon brushes of superior quality (d) using equiliser rings Ans: c
517. In D.C. generators, lap winding is used for (a) high voltage, high current (b) low voltage, high current (c) high voltage, low current (d) low voltage, low current Ans: b
518. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
(a) 2 : 3 (b) 3 : 1 (c) 3 : 2 (d) 1 : 3 Ans: b
519. The voltage drop for which of the following types of brush can be expected to be least ?
(a) Graphite brushes (b) Carbon brushes (c) Metal graphite brushes (d) None of the above Ans: c
520. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains , if the speed of the generator is doubled, the e.m.f. generated will be (a) E/2 (b) 2E (c) slightly less than E (d) E Ans: b
521. In a D.C. generator the actual flux distribution depends upon (a) size of air gap (b) shape of the pole shoe (c) clearance between tips of the adjacent pole shoes (d) all of the above Ans:d
522. The armature core of a D.C. generator is usually made of
(a) silicon steel (b) copper (c) non-ferrous material (d) cast-iron Ans: a
523. Satisfactory commutation of D.C. machines requires
(a) brushes should be of proper grade and size (b) brushes should smoothly run in the holders (c) smooth, concentric commutator properly undercut (d) all of the above Ans: d
524. Open circuited armature coil of a D.C. machine is (a) identified by the scarring of the commutator segment to which open circuited coil is connected (b) indicated by a spark completely around the commutator (c) both (a) and (b) (d) none of the above Ans: c
525. In a D.C. machine, fractional pitch winding is used
(a) to increasethe generated voltage (b) to reduce sparking (c) to save the copper because of shorter end connections (d) due to (b) and (c) above Ans:
526. For the parallel operation of two or more D.C. compound generators, we should ensure that
(a) voltage of the incoming generator should be same as that of bus bar (b) polarity of incoming generator should be same as that of bus bar (c) all the series fields should be run in parallel by means of equilizer connection (d) series fields of all generators should be either on positive side or negative side of the armature (e) all conditions mentioned above should be satisfied Ans: d
527. D.C. series generator is used (a) to supply traction load (b) to supply industrial load at constant voltage (c) voltage at the toad end of the feeder (d) for none of the above purpose Ans: c
528. Following D.C. generator will be in a position to build up without any magnetism in the poles (a) series generator (b) shunt generator (c) compound generator (d) self-excited generator Ans: d
529. Interpole flux should be sufficient to (a) neutralise the commutating self induced e.m.f. (b) neutralise the armature reaction flux (c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil (d) perform none of the above functions Ans: c
530. D.C. generator generally preferred for charging automobile batteries is (a) series generator (b) shunt generator (c) long shunt compound generator (d) any of'the above Ans: c
531. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when (a) r.p.m. is more than 300 (b) r.p.m. is less than 300 (c) number of poles is 4 (d) number of poles is 2 Ans: d
532. Permeance is the reciprocal of
(a) flux density (b) reluctance (c) ampere-turns (d) resistance Ans: b
533. In D.C. generators the polarity of the interpoles (a) is the same as that of the main pole ahead
(b) is the same as that of the immediately preceding pole (c) is opposite to that of the main pole ahead (d) is neutral as these poles do not play part in generating e.m.f. Ans: a
534. The e.m.f. generated in a D.C. generator is directly proportional to
(a) flux/pole (b) speed of armature (c) number of poles (d) all of the above Ans: b
535. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when (a) there is no load on|he generator (b) the generator runs on full load (c) the generator runs on overload (d) the generator runs on designed speed Ans: a
536. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except
(a) interpoles (b) dummy coils (c) compensating winding (d) shifting of axis of brushes Ans: b
537. In D.C. generators on no-load, the air gap flux distribution in space is
(a) sinusoidal (b) triangular (c) pulsating (d) flat topped Ans: d
538. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly (a) 150 V (b) 175 V (c) 240 V (d) 290 V Ans: c
539. The purpose of providing dummy coils in a generator is (a) to reduce eddy current losses (b) to enhance flux density (c) to amplify voltage (d) to provide mechanical balance for the rotor Ans: d 540. In a shunt generator the voltage build up is generally restricted by
(a) speed limitation (b) armature heating (c) insulation restrictions (d) saturation of iron Ans:
541. If a D.C. generator fails to build up the probable cause could not be (a) imperfect brush contact (b) field resistance less than the critical resistance (c) no residual magnetism in the generator (d) faulty shunt connections tending to reduce the residual magnetism Ans: b
542. Flashing the field of D.C. generator means (a) neutralising residual magnetism (b) creating residual magnetism by a D.C. source (c) making the magnetic losses of forces parallel (d) increasing flux density by adding extra turns of windings on poles Ans: b
543. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
(a) 640 V (b) 620 V (c) 600 V (d) 580 V Ans: d
544. In a D.C. generator the critical resistance refers to the resistance of
(a) brushes (b) field (c) armature (d) load Ans: b
545. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them (a) just ahead of magnetic neutral axis (b) in magnetic neutral axis (c) just behind the magnetic neutral axis Ans: a
546. Armature coil is short circuited by brushes when it lies (a) along neutral axis (b) along field axis (c) in any of the above positions (d) in none of the above positions Ans: a
547. A cumulatively compounded long shunt generator when operating as a motor would be
(a) cumulatively compounded long shunt (b) differentially compounded long shunt (c) cumulatively compounded short shunt (d) differentially compounded short shunt Ans: b
548. To avoid formation of grooves in the commutator of a D.C. machine
(a) the brushes of opposite polarity should track each other (b) the brushes of same polarity should track each other (c) brush position has no effect on the commutator grooving Ans: a
549. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two com-mutator bars (6) Insulation failure between two turns of a coil (c) Two of more turns of the same coil getting grounded (d) All of the above Ans: d
550. The rapid wear of brushes takes place due to
(a) abrasion from dust (b) excessive spring pressure (c) rough commutator bars (d) high mica insulation between com-mutation bars (e) all of the above factors Ans: e
551. Number of tappings for each equilizer ring is equal to (a) number of pole pairs (b) number of poles (c) number of parallel paths (d) number of commutator segments Ans: a
552. A D.C. generator can be considered as
(a) rectifier (b) primemover (c) rotating amplifier (d) power pump Ans: c
553. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called (a) rotor (b) stator (c) field (d) armature Ans: d
554. In a D.C. machine stray loss is the sum of
(a) total copper loss and mechanical loss (b) armature copper loss and iron loss (c) shunt field copper loss and mechanical loss (d) iron loss and mechanical loss Ans: d
555. Lap winding is composed of
(a) any even number of conductors (b) any odd number of conductors (c) that even number which is exact multiple of poles + 2 (d) that even number which is exact multiple of poles Ans: a
556. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will (a) increase (b) decrease (c) remain unaffected (d) fluctuate heavily Ans: b
557. An exciter for a turbo generator is a
(a) separately excited generator (b) shunt generator
(c) series generator (d) compound generator Ans: b
558. In case of a flat compounded generator (a) voltage generated is less than the rated voltage
b) generated voltage is proportional to the load on the generator (c) voltage remains constant irrespective of the load (d) speed varies in proportion to the load on the generator Ans: c
559. Which of the following generator will have negligible terminal voltage while running on no-load ? (a) Series generator (b) Shunt generator (c) Compound generator
(d) Separately excited generator Ans: a
560. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
(a) Series generator (b) Shunt generator (c) Compound generator (d) None of the above Ans: d
561. In over compounded generator, full load terminal voltage is (a) almost zero (b) less than noload terminal voltage (c) more than noload terminal voltage (d) equal to no-load terminal voltage Ans: c 562. In a level compounded D.C. generator, full load terminal voltage is
(a) negligibly low (b) equal to no-load terminal voltage (c) more than no-load terminal voltage (d) less than no-load terminal voltage Ans: b
563. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except (a) armature reaction (b) armature resistance drop (c) field weakening due to armature reaction and armature (d) commutation Ans: d
564. In a D.C. generator
(a) external resistance = internal char-acteristic - armature reaction (b) internal characteristic = magnetisation characteristic - ohmic drop (c) external characteristic = magnetisation characteristic - ohmic drop - armature reaction (d) magnetisation characteristic = external characteristic Ans: c
565. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave (a) will be zero (b) will be of 5 Hz (c) willbeof5xiVHz (d) will be of v Hz 5 Ans: b
566. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be (a) zero (b) about 2 V (c) about 50 V (d) 220 V Ans: b
567. In a separately excited generator supplying rated load the armature reaction ,
(a) is always present (b) is always absent (c) may be sometimes present (d) none of the above Ans: a
568. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
(a) zero (b) small (c) the same as rated voltage (d) high Ans: a
569. Armature reaction in a generator results in (a) demagnetisation of leading pole tip and magnetisation of trailing pole tip (b) demagnetisation of trailing pole tip and magnetisation of leading pole tip (c) damagnetising the centre of all poles (d) magnetising the centre of all poles Ans: a
570. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
(a) Series field (b) Compensating field (c) Inter pole field (d) Shunt field Ans: d
571. Wave winding is composed of
(a) any even number of conductors (b) any odd number of conductors (c) that even number which is exact multiple of poles + 2 (d) that even number which is exact multiple of poles Ans: c
572. The critical resistance of the D.C. generator is the resistance of
(a) field (b) brushes (c) armature (d) load Ans: a
573. When two D.C. series generators are running in parallel, an equilizer bar is used
(a) to increase the speed and hence generated e.m.f. (b) to increase the series flux (c) so that two similar machines will pass approximately equal currents to the load (d) to reduce the combined effect of ar-mature reaction of both machines Ans: c
574. Which of the following generating machine will offer constant voltage on all loads ?
(a) Self-excited generator (b) Separately excited generator
(c) Level compounded generator .(d) All of the above Ans: c
575. Which of the following generators will be preferred if they are required to be run in parallel
(a) Shunt generators (b) Series generators (c) Compound generators (d) None of the above Ans: a
576. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?
(a) The direction of that generator is reversed (b) The speed of that generator is increased (c) The field of that generator is weakened (d) That generator takes large share of loads Ans: d
577. A D.C. generator works on the principle of (a) Lenz's law (b) Ohm's law
(c) Faraday's law of electromagnetic induction (d) none of the above Ans: c
578. A series generator can self-excite (a) only if the load current is zero (b) only if the load current is not zero (c) irrespective of the value of load current (d) none of the above Ans: b
579. A shunt generator can self-excite
(a) only if the resistance of the field circuit is less than critical value (b) only if the resistance of the field circuit is critical value (c) irrespective of the value of the resis-tance in the field circuit Ans: a
580. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
(a) 150 V (b) less than 150 V (c) greater than 150 V (d) none of the above Ans: c
581. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
(a) will be less than 250 V (b) will always be 250 V
(c) may be greater or less than 250 V (d) none of the above Ans: c
582. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be (a) 270 V (b) 267.5 V (c) 265 V (d) 257.4 V Ans: b 583. The essential condition for parallel operation of two D.C. generators is that they have '
(a) same kW rating (b) the same operation r.p.m.
(c) the same drooping voltage charac-teristics (d) same percentage regulation Ans: c
584. When two D.C. generators are running in parallel an equilizer bar is used
(a) to increase the series flux (b) to increase the generated e.m.f. (c) to reduce the combined effect of ar-mature reaction of both the machines (d) so that the two identical machines will pass approximately equal currents to the load Ans: d
585. With a D.C. generator which of the following regulation is preferred ?
(a) 100% regulation (b) infinite regulation (c) 50% regulation (d) 1% regulation Ans: d
586. Which generator would you prefer for feeding long D.C. transmission lines ?
(a) Series generator (b) Shunt generator
(c) Over compound generator (d) Flat compound generator Ans: c
587. In a D.C. generator the critical resistance can be increased by (a) increasing its field resistance (b) decreasing its field resistance (c) increasing its speed (d) decreasing its speed Ans: c
588. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is (a) 2 (b) 4 (c) 6 (d) 8 Ans: b
589. For both lap and wave windings, there are as many commutator bars as the number of
(a) slots (b) armature conductors (c) winding elements (d) poles Ans: c
590. The series field of a short-shunt D.C. generator is excited by
(a) external current (b) armature current (c) shunt current (d) load current Ans: d
591. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately (a) 40 percent (b) 25 percent (c) 10 percent (d) 5 percent Ans: d
592. Shunt generators are most suited for stable parallel operation because of their
(a) rising voltage characteristics (b) identical voltage characteristics (c) drooping voltage characteristics (d) linear voltage characteristics Ans: c
593. The main factor which leads to unstable parallel operation of flat and over compounded generators is (a) their rising voltage characteristics (b) unequal number of turns in their series field windings (c) unequal speed regulation of their primemovers (d) unequal series field resistances Ans: a 594. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first is to (a) reverse the field connections (b) increase the field resistance
(c) increase the speed of primemover (d) check armature insulation resistance Ans: a
595.No-load speed of which of the following motor will be highest ?
(a) Shunt motor (b) Series motor (c) Cumulative compound motor
(d) Differentiate compound motor Ans: b
596. The direction of rotation of a D.C. series motor can be changed by
(a) interchanging supply terminals (b) interchanging field terminals
(c) either of (a) and (b) above (d) None of the above Ans: b
597. Which of the following application requires high starting torque ?
(a) Lathe machine (b) Centrifugal pump (c) Locomotive (d) blower Ans: c
598. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ? (a) Series motor (b) Shunt motor (c) Differentially compound motor (d) Cumulative compound motor Ans: a 599. Which D.C. motor will be preferred for machine tools ? (a) Series motor (b) Shunt motor (c) Cumulative compound motor (d) Differential compound motor Ans: b
600. Differentially compound D.C. motors can find applications requiring
(a) high starting torque (b) low starting torque (c) variable speed (d) frequent on-off cycles Ans: b 601. Which D.C. motor is preferred for elevators ?
(a) Shunt motor (b) Series motor (c) Differential compound motor
(d) Cumulative compound motor Ans: d
602. According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of (a) current in the conductor aovtaat of conductor (c) resultant force on conductor (d) none of the above Ans: a
603. If the field of a D.C. shunt motor gets opened while motor is running
(a) the speed of motor will be reduced % (b) the armature current will reduce (c) the motor will attain dangerously high speed 1 (d) the motor will continue to nuvat constant speed Ans: c
604. Starters are used with D.C. motors because
(a) these motors have high starting torque (b) these motors are not self-starting (c) back e.m.f. of these motors is initially (d) to restrict armature current as there is no back e.m.f. while starting Ans: d
605. In D.C. shunt motors as load is reduced
(a) the speed will increase abruptly (b) the speed will increase in proportion to reduction in load
(c) the speed will remain almost/constant (d) the speed will reduce Ans: c
606. A D.C. series motor is that which (a) has its field winding consisting of thick wire and less turns (b) has a poor torque (c) can be started easily without load (d) has almost constant speed Ans: a
607. For starting a D.C. motor a starter is required because (a) it the speed of the motor
(b) it limits the starting current to a safe value (c) it starts the motor (d) none of the above Ans: b
608. The type of D.C. motor used for shears and punches is (a) shunt motor (b) series motor (c) differential compoutid D.C. motor (d) cumulative compound D.C. motor Ans: d
609. If a D.C. motor is connected across the A.C. supply it will (a) run at normal speed (b) not run (c) run at lower speed (d) burn due to heat produced in the field winding by eddy currents Ans: d
610. To get the speed of D.C, motor below the normal without wastage of electrical energy is used. (a) Ward Leonard control (b) rheostatic control (c) any of the above method (d) none of the above method Ans: a
611. When two D.C. series motors are connected in parallel, the resultant speed is
(a) more than the normal speed (b) loss than the normal speed (c) normal speed (d) zero Ans: c
612. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
(a) decreasing the field current (b) increasing the field current
(c) decreasing the armature current (d) increasing the armature current Ans: a
613. In a D.C. shunt motor, speed is
(a) independent of armature current (b) directly proportional to the armature current (c) proportional to the square of the current (d) inversely proportional to the armature current Ans: a
614. A direct on line starter is used: for starting motors
(a) iip to 5 H.P. (b) up to 10 H.P. (c) up to 15 H.P. (d) up to 20 H.P. Ans: a
615. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? (a) The motor will stop (b) The motor will continue to run (c) The armature may burn (d) The motor will run noisy Ans: c 616. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
(a) back e.m.f. is equal to armature drop (b) armature drop is negligible (c) flux is proportional to armature current (d) flux is practically constant in D:C. shunt motors Ans: d
617. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be (a) almost negligible (b) rated full-load current (c) less than full-load current
(d) more than full-load current Ans: d
618. These days D.C. motors are widely used in
(a) pumping sets (b) air compressors (c) electric traction (d) machine shops Ans: c
619. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor? (a) Frame (b) Shaft (c) Commutator (d) Stator Ans: c
620. In which of the following applications D.C. series motor is invariably tried?
(a) Starter for a car (b) Drive for a water pump (c) Fan motor (d) Motor in A.C. or D.C. Ans: a
621. In D.C. machines fractional pitch winding is used (a) to improve cooling (b) to reduce copper losses (c) to increase the generated e.m.f. (d) to reduce the sparking Ans: d
622. A three point starter is considered suitable for (a) shunt motors (b) shunt as well as compound motors (c) shunt, compound and series motors (d) all D.C. motors Ans: b
623. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
(a) 100% (b) around 90% (c) anywhere between 75% and 90% (d) less than 50% Ans: d
624. The ratio of starting torque to full-load torque is least in case of
(a) series motors (b) shunt motors (c) compound motors (d) none of the above Ans: b
625. In D.C. motor which of the following can sustain the maximum temperature rise? (a) Slip rings (b) Commutator (c) Field winding (d) Armature winding Ans: c
626. Which of the following /rule can he used to determine the direction of rotation of D.C. motor
(a) Lenz's law (b) Faraday's law (c) Coloumb's law (d) Fleming's left-hand rule Ans: d
627. Which of the following load normally needs starting torque more than the rated torque?
(a) Blowers (b) Conveyors (c) Air compressors (d) Centrifugal pumps Ans: b
628. The starting resistance of a D.C. motor is generally
(a) low (b) around 500 Q (c) 1000 Q (d) infinitely large Ans: a
629. The speed of a D.C. series motor is
(a) proportional to the armature current (b) proportional to the square of the armature current (c) proportional to field current (d) inversely proportional to the armature current Ans: d
630. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to (a) 100% of the previous value (b) 50% of the previous value (c) 25% of the previous value (d) 10% of the previous value (e) none of the above Ans: c
631. The current drawn by the armature of D.C. motor is directly proportional to (a) the torque required (b) the speed of the motor (c) the voltage across the terminals (d) none of the above Ans: a 632. The power mentioned on the name plate of an electric motor indicates (a) the power drawn in kW (b) the power drawn in kVA (c) the gross power (d) the output power available at the shaft Ans: d 633. Which D.C. motor has got maximum self loading property? (a) Series motor (b) Shunt motor (c) Cumulatively compounded 'motor (d) Differentially compounded motor Ans: d
634. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
(a) Series motor (b) Shunt motor (c) Cumulatively compounded motor
(d) Differentially compounded motor Ans: c
635. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
(a) nothing will happen to th£ motor (b) this will make armature to take heavy current, possibly burning it (c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses (d) motor will run at very slow speed Ans: c
636. D.C. series motors are used (a) where load is constant (b) where load changes frequently
(c) where constant operating speed is needed (d) in none of the above situations. Ans: d
637. For the same H.P. rating and full load speed, following motor has poor starting torque
(a) shunt (b) series (c) differentially compounded (d) cumulativelyc'ompounded Ans: c
638. In case of conductively compensated D.C. series motors, the compensating winding is provided (a) as separately wound unit (6) in parallel with armature winding
(c) in series with armature winding (d) in parallel with field winding Ans: c
639. Sparking at the commutator of a D.C. motor may result in (a) damage to commutator segments (b) damage to commutator insulation (c) increased power consumption (d) all of the above Ans: d 640. Which of the following motor is preferred for operation in highly explosive atmosphere ?
(a) Series motor (b) Shunt motor (c) Air motor (d) Battery operated motor Ans: c
641. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
(a) Starting torque (b) Operating speed (c) Full-load current (d) All of the above Ans: c
642. Which one of the following is not the function of pole shoes in a D.C. machine ?
(a) To reduce eddy current loss (b) To support the field coils (c) To spread out flux for better unifor-mity (d) To reduce the reluctance of the mag-netic path Ans: a
643. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is (a) 4.0 (b) 2.0 (c) 1.0 (d) 0.5 Ans: d
644. The condition for maximum power in case of D.C. motor is
(a) back e.m.f. = 2 x supply voltage (b) back e.m.f. =1 /2x supply voltage (c) supply voltage = 1/2 x back e.m.f. (d) supply voltage = back e.m.f. Ans: b
645. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
(a) Low speed operation (b) High speed operation (c) Variable speed operation
(d) Fixed speed operation Ans: c
646. In D.C. machines the residual magnetism is of the order of
(a) 2 to 3 per cent (6) 10 to 15 per cent (c) 20 to 25 per cent (d) 50 to 75 per cent Ans: a
647. Which D.C. motor is generally preferred for cranes and hoists ? (a) Series motor (b) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor Ans: a
648. Three point starter can be used for (a) series motor only (b) shunt motor only (c) compound motor only (d) both shunt and compound motor Ans: d
649. Sparking, is discouraged in a D.C. motor because (a) it increases the input power con-sumption (b) commutator gets damaged (c) both (a) and (b) (d) none of the above Ans: b
650. Speed control by Ward Leonard method gives uniform speed variation (a) in one direction
(b) in both directions (c) below normal speed only (d) above normal speed only. Ans: b
651. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be (a) level compounded (b) under compounded
(c) cumulatively compounded (d) differentially compounded Ans: c
652. Following motor is used where high starting torque and wide speed range control is required.
(a) Single phase capacitor start (b) Induction motor (c) Synchronous motor
(d) D.C. motor (e) None of the above Ans: d
653. In a differentially compounded D.C. motor, if shunt field suddenly opens
(a) the motor will first stop and then run in opposite direction as series motor (b) the motor will work as series motor and run at slow speed in the same direction (c) the motor will work as series motor and run at high speed in the same direction (d) the motor will not work and come to stop Ans: a
654. Which of the following motor has the poorest speed regulation ? (a) Shunt motor (b) Series motor (c) Differential compound motor (d) Cumulative compound motor Ans: b
655. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
(a) D.C. series motor (b) D.C. shunt motor (c) induction motor (d) all of above motors Ans: a
656. As -the load is increased the speed of D.C. shunt motor will
(a) reduce slightly (b) increase slightly (c) increase proportionately (d) remains unchanged Ans: a 657. The armature torque of the D.C. shunt motor is proportional to
(a) field flux only (b) armature current only (c) both (a) and (b) (d) none of the above Ans: b
658. Which of the following method of speed control of D.C. machine will offer minimum efficiency ? (a) Voltage control method (b) Field control method
(c) Armature control method (d) All above methods Ans: c
659. Usually wide and sensitive speed control is desired in case of
(a) centrifugal pumps (b) elevators (c) steel rolling mills (d) colliery winders Ans: d
660. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is (a) 2.36% (6) 4.76% (c) 6.77% (d) 8.84% Ans: b
661. The armature voltage control of D.C. motor provides (a) constant torque drive (b) constant voltage drive (c) constant current drive (d) none of the above Ans: a
662. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit (a) a resistance is connected in series with armature (b) a resistance is connected parallel to the armature (c) armature is temporarily open circuited
(d) a high value resistor is connected across the field winding Ans: a
663. The speed of a D.C. shunt motor can be increased by (a) increasing the resistance in armature circuit (b) increasing the resistance in field circuit (c) reducing the resistance in the field circuit
(d) reducing the resistance in the armature circuit Ans: b
664. If I2 be the armature current, then speed of a D.C. shunt motor is (a) independent of Ia
(b) proportional to la (c) varies as (Ia) (d) varies as la Ans: a
665. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
(a) remain unchanged (b) reduce to one-fourth value (c) increase four folds (d) be doubled Ans: a
666. At the instant of starting when a D.C. motor is put on supply, it behaves like (a) a highly resistive circuit (6) a low resistance circuit (c) a capacitive circuit (d) none of the above Ans: b
667. The speed of a D.C. motor can be varied by varying (a) field current (b) applied voltage
(c) resistance in series with armature (d) any of the above Ans: d
668. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ? (a) Low cost (b) Wide speed range (c) Stability (d) High starting torque. Ans: a
669. For a D.C. shunt motor if the excitation is changed
(a) torque will remain constant (b) torque will change but power will remain constant (c) torque and power both will change (d) torque, power and speed, all will change Ans: b
670. Which motor has the poorest speed control? (a) Differentially compounded motor (b) Cumulatively compounded motor (c) Shunt motor (d) Series motor Ans: d
671. The plugging gives the (a) zero torque braking (b) smallest torque braking
(c) highest torque braking (d) none of the above Ans: c
672. The armature voltage control of D.C. motor provides
(a) constant voltage drive (b) constant current drive
(c) constant torque drive (d) none of the above Ans: c
673. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor (a) of lower H.P. should be selected (6) of higher H.P. should be selected (c) can be used for 50°C ambient temperature also (d) is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor Ans: d
674. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
(a) regenerative (b) plugging (c) dynamic braking (d) none of the above (e) any of the above Ans: b
675. Which of the following motors one will choose to drive the rotary compressor ?
(a) D.C. shunt motor (b) D.C. series motor (c) Universal motor (d) Synchronous motor Ans: d
676. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
(a) increase (b) decrease (c) remain same (d) become zero Ans: a
677. Why are the D.C. motors preferred for traction applications ? (a) Torque and speed are inversely proportional to armature current (b) Torque is proportional to armature current (c) Torque is proportional to square root of armature current (d) The speed is inversely proportional to the torque and the torque is proportional to square of armature current Ans: d
678. Which of the following motors is usually used in house-hold refrigerators ?
(a) D.C. shunt motor (b) D.C. series motor (c) Single phase induction motor (split phase start or induction run motor) (d) Reluctance motor (e) Synchronous motor Ans: c
679. Which of the following motors is most suitable for signalling and many kinds of timers ?
(a) D.C. shunt motor (b) D.C. series motor (c) Induction motor (d) Reluctance motor Ans: d
680. Which motor should not be started on no-load ? (a) Series motor (b) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor. Ans: a
681. Ward-Leonard control is basically a (a) voltage control method (b) field divertor method
(c) field control method (d) armature resistance control method Ans: a
682. For constant torque drive which speed control method is preferred ? (a) Field control (b) Armature voltage control (c) Shunt armature control (d) Mechanical loading system Ans: b
683. In Ward-Leonard control the lower limit of speed is imposed by
(a) residual magnetism of the generator (b) core losses of motor
(c) mechanical losses of motor and generator together (d) all of the above Ans: a
684. The main disadvantage of the Ward-Leonard control method is (a) high initial cost (b) high maintenance cost (c) low efficiency at Hght loads (d) all of the above Ans: d
685. Regenerative method of braking is based on that
(a) back e.m.f. is less than the applied voltage (b) back e.m.f. is equal to the applied voltage (c) back e.m.f. of rotor is more than the applied voltage (d) none of the above Ans: b
686. The hysteresis loss in a D.C. machine least depends on
(a) Frequency of magnetic reversals (b) Maximum value of flux density
(c) Volume and grade of iron (d) Rate of flow of ventilating air Ans: d
687. In a D.C. generator all of the following could be the effects of iron losses except
(a) Loss of efficiency (b) Excessive heating of core (c) Increase in terminal voltage
(d) Rise in temperature of ventilating air Ans: c
688. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
(a) hysteresis loss (b) field copper loss (c) armature copper loss (d) eddy current loss Ans: c
689. Which of the following loss in a D.C. generator varies significantly with the load current ?
(a) Field copper loss (b) Windage loss (c) Armature copper loss (d) None of the above Ans: c
690. Torque developed by a D.C. motor depends upon
(a) magnetic field (b) active length of the conductor (c) current flow through the conductors (d) number of conductors (e) radius of armature (f) all above factors Ans: f
691. D.C. shunt motors are used for driving
(a) trains (b) cranes (c) hoists (d) machine tools Ans: d 692. In a manual shunt motor starter (a) over load is connected in series and no volt relay in parallel with the load (6) over load relay is connected in parallel and no volt relay in series with the load
(c) over load relay and no volt relay are both connected in series with the load (d) over load relay and no volt relay are both connected in parallel with the load Ans: a
693. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ? (a) Providing laminations in armature core (b) Providing laminations in stator
(c) Using non-magnetic material for frame
(d) Using material of low hysteresis co-efficient for armature core material Ans: d
694. Which of the following loss in a D.C. generator is dissipated in the form of heat?
(a) Mechanical loss (b) Core loss (c) Copper loss (d) All of the above Ans: d
695. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ? (a) Hysteresis losses (b) Eddy current losses (c) Copper losses (d) Windage losses Ans: b 696. The total losses in a well designed D.C. generator of 10 kW will be nearly
(a) 100 W (b) 500 W (c) 1000 W (d) 1500 W Ans: b
697. The condition for maximum efficiency for a D.C. generator is
(a) eddy current losses = stray losses (b) hysteresis losses = eddy current losses (c) copper losses = 0 (d) variable losses = constant losses Ans: d 698. D.C. generators are normally designed for maximum efficiency around (a) full-load (b) rated r.p.m. (c) rated voltage (d) all of the above Ans: a
699. In a D.C. generator, the iron losses mainly take place in
(a) yoke (b) commutator (c) armature conductors (d) armature rotor Ans: d
700. D.C. generators are installed near the load centres to reduce
(a) iron losses (b) line losses (c) sparking (d) corona losses Ans: b
701. The purpose of retardation test on D.C. shunt machines is to find out
(a) stray losses (b) eddy current losses (c) field copper losses (d) windage losses Ans: a
702. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ? (a) Swinburne's test (b) Hopkinson's test (c) Field test (d) Brake test Ans: c
703. Hopkinson's test on D.C. machines is conducted at
(a) no-load (b) part load (c) full-load (d) overload Ans: c
704. During rheostat braking of D.C. series motors (a) motor is run as a generator
(b) motor is reversed in direction (c) motor is run at reduced speed Ans: a
705. For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors (b) Series motors (c) Compound motors (d) All of the above Ans: d
706. Which method of braking is generally used in elevators ?
(a) Plugging (b) Regenerative braking (c) Rheostatic braking (d) None of the above Ans: a
707. In variable speed motor (a) a stronger commutating field is needed at low speed than at high speed (b) a weaker commutating field is needed at low speed than at high speed (c) same commutating field is needed at low speed than at high speed (d) none of the above is correct Ans: b 708. When the armature of a D.C. motor rotates, e.m.f. induced is
(a) self-induced e.m.f. (b) mutually induced e.m.f. (c) back e.m.f. (d) none of the above Ans: c
709. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control (a) drum type controller is used (b) three point starter is used
(c) four point starter is used (d) all above can be used Ans: a
710. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a) this will make armature to take heavy current, possibly burning it (6) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
(c) nothing will happen to motor (d) motor will come to stop Ans: a
711. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the
(a) series motor (b) shunt motor (c) compound motor (d) any of the above Ans: a
712. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
(a) series motor (b) shunt motor (c) compound motor (d) any of the above Ans: c
713. Which D.C. motor has got maximum self relieving property ? (a) Series motor (6) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor Ans: a
714. In the D.C. motor the iron losses occur in
(a) the field (b) the armature (c) the brushes (d) the commutator Ans: b
715. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by (a) reducing the field current (b) decreasing the armature current (c) increasing the armature current (d) increasing the excitation current (e) none of the above methods Ans:a
716 One D.C. motor another D.C. motor. The second D.C.motor when excited and driven
(a) runs as a generator (b) does not run as a generator
(c) also runs as a motor comes to stop after sometimeAns:a
717. The insulating material for a
(a) low cost (b) high dielectric strength (c) high mechanical strength (d) all of the above Ans: d
718. Which of the following protects a cable against mechanical injury ?
(a) Bedding (b) Sheath (c) Armouring (d) None of the above Ans: c
719. Which of the following insulation is used in cables ?
(a) Varnished cambric (b) Rubber (c) Paper (d) Any of the above Ans: d
720. Empire tape is (a) varnished cambric (b) vulcanised rubber (c) impregnated paper (d) none of the above Ans: a
721. The thickness of the layer of insulation on the conductor, in cables, depends upon
(a) reactive power (b) power factor (c) voltage (d) current carrying capacity Ans: c
722. The bedding on a cable consists of
(a) hessian (b) (c) any of the above (d) none of the above Ans: c
723. The insulating material for cables should
(a) be acid proof (b) be non-inflammable (c) be non-hygroscopic (d) have all above properties Ans: d
724. In a cable immediately above metallic sheath is provided.
(a) earthing connection (b) bedding (c) armouring (d) none of the above Ans: b
725. The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to
(a) absence of harmonics (b) non-existence of any stability limit (c) smaller dielectric loss
(d) absence of ripples (e) none of the above Ans: c
726. In case of three core flexible cable the colour of the neutral is
(a) blue (b) black (c) brown (d) none of the above Ans: a
727. cables are used for 132 kV lines.
(a) High tension (b) Super tension (c) Extra high tension (d) Extra super voltage Ans: d
728. Conduit pipes are normally used to protect cables.
(a) unsheathed cables (b) armoured (c) PVC sheathed cables (d) all of the above Ans: a
729. The minimum dielectric stress in a cable is at
(a) armour (b) bedding (c) conductor surface (d) lead sheath Ans: d
730. In single core cables armouring is not done to (a) avoid excessive sheath losses (b) make it flexible (c) either of the above (d) none of the above Ans: a
731. Dielectric strength of rubber is around
(a) 5 kV/mm (b) 15 kV/mm (c) 30 kV/mm (d) 200 kV/mm Ans: c
732. Low tension cables are generally used upto
(a) 200 V (b) 500 V (c) 700 V (d) 1000 V Ans: d 733. In a cable, the maximum stress under operating conditions is at (a) insulation layer (b) sheath (c) armour (d) conductor surface Ans: d
733. In a cable, the maximum stress under operating conditions is at
(a) insulation layer (b) sheath (c) armour (d) conductor surface Ans: d
734. High tension cables are generally used upto (a) 11kV (b) 33kV (c) 66 kV (d) 132 kV Ans: a
735. The surge resistance of cable is (a) 5 ohms (b) 20 ohms (c) 50 ohms (d) 100 ohms Ans: c
736. PVC stands for (a) polyvinyl chloride (b) post varnish conductor (c) pressed and varnished cloth (d) positive voltage conductor (e) none of the above Ans: a
737. In the cables, the location of fault is usually found out by comparing
(a) the resistance of the conductor (b) the inductance of conductors
(c) the capacitances of insulated conductors (d) all above parameters Ans: c
738. In capacitance grading of cables we use a dielectric.
(a) composite (b) porous (c) homogeneous (d) hygroscopic Ans: a
739. Pressure cables are generally not used beyond (a) 11 kV (b) 33 kV (c) 66 kV (d) 132 kV Ans: c 740. The material for armouring on cable is usually
(a) steel tape (b) galvanised steel wire (c) any of the above (d) none of the above Ans: c
741. Cables, generally used beyond 66 kV are (a) oil (b) S.L. type (c) belted (d) armoured Ans: a
742. The relative permittivity of rubber is
(a) between 2 and 3 (b) between 5 and 6 (c) between 8 and 10 (d) between 12 and 14 Ans: a
743. Solid type cables are considered unreliable beyond 66 kV because
(a) insulation may melt due to higher temperature (b) skin effect dominates on the conductor
(c) of corona loss between conductor and sheath material
(d) there is a danger of breakdown of insulation due to the presence of voids Ans: d
744. If the length of a cable is doubled, its capacitance
(a) becomes one-fourth (b) becomes one-half (c) becomes double (d) remains unchanged Ans: c
745. In cables the charging current
(a) lags the voltage by 90° (b) leads the voltage by 90° (c) lags the voltage by 180° (d) leads the voltage by 180° Ans: b
746. A certain cable has an insulation of relative permittivity 4. If the insulation is replaced by one of relative permittivity 2, the capacitance of the cable will become
(a) one half (6) double (c) four times (d) none of the above Ans: a
747. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be (a) 5 kV/mm (b) 10 kV/mm (a) 15 kV/mm (d) 30 kV/mm Ans: b
748. In the cables, sheaths are used to (a) prevent th from entering the cable `
(b) provide enough strength (e) provide proper insulation (d) none of the above Ans: a
749. The intersheaths in the cables are used to (a) minimize the stress (b) avoid the requirement of good insulation (c) provide proper stress distribution (d) none of the above Ans: c
750. The electrostatic stress in underground cables is (a) same at the conductor and the sheath (b) minimum at the conductor and maximum at the sheath (c) maximum at the conductor and minimum at the sheath (d) zero at the conductor as well as on the sheath (e) none of the above Ans: c
751. The breakdown of insulation of the cable can be avoided economically by the use of
(a) inter-sheaths (b) insulating materials with different dielectric constants
(c) both (a) and (b) (d) none of the above Ans: c
752. The insulation of the cable decreases with (a) the increase in length of the insulation
(b) the decrease in the length of the insulation (c) either (a) or (b) (d) none of the above Ans: a
753. A cable carrying alternating current has
(a) hysteresis losses only (b) hysteresis and leakage losses only (c) hysteresis, leakage and copper losses only (d) hysteresis, leakage, copper and friction losses Ans: b
754. In a cable the voltage stress is maximum at
(a) sheath (6) insulator (e) surface of the conductor (d) core of the conductor Ans: d
755. Capacitance grading of cable implies
(a) use of dielectrics of different permeabilities (b) grading according to capacitance of cables per km length (c) cables using single dielectric in different concentrations (d) capacitance required to be introduced at different lengths to counter the effect of inductance (e) none of the above Ans: a
756. Underground cables are laid at sufficient depth (a) to minimise temperature stresses (b) to avoid being unearthed easily due to removal of soil (c) to minimise the effect of shocks and vibrations due to gassing vehicles, etc. (d) for all of the above reasons Ans: c
757. The advantage of cables over overhead transmission lines is (a) easy maintenance (b) low cost (c) can be used in congested areas (d) can be used in high voltage circuits Ans: c
758. The thickness of metallic shielding on cables is usually
(a) 0.04 mm (b) 0.2 to 0.4 mm (e) 3 to 5 mm (d) 40 to 60 mm Ans: a
759. Cables for 220 kV lines are invariably (a) mica insulated (b) paper insulated (c) compressed oil or compressed gas insulated (d) rubber insulated (e) none of the above Ans: c
760. Is a cable is to be designed for use on 1000 kV, which insulation would you prefer ?
(a) Polyvinyle chloride (b) Vulcanised rubber (c) Impregnated paper
(d) Compressed SFe gas(e) none of the above Ans: d
761. If a power cable and a communication cable are to run parallel the minimum distance between the two, to avoid interference, should be (a) 2 cm (b) 10 cm (c) 50 cm (d) 400 cm Ans: c
762. Copper as conductor for cables is used as
(a) annealed (b) hardened and tempered (c) hard drawn (d) alloy with chromium Ans: a
763. The insulating material should have
(a) low permittivity (b) high resistivity (c) high dielectric strength (d) all of the above Ans: d
764. The advantage of oil filled cables is (a) more perfect impregnation (b) smaller overall size
(c) no ionisation, oxidation and formation of voids (d) all of the above Ans: d
765. The disadvantage with paper as insulating material is (a) it is hygroscopic (6) it has high capacitance (c) it is an organic material (d) none of the above Ans: a
766. The breakdown voltage of a cable depends on (a) presence of moisture
(b) working temperature (c) time of application of the voltage (d) all of the above Ans: d
767. It is difficult to maintain oil filled cables. (a) Yes (b) No Ans: a
768. In capacitance grading a homogeneous dielectric is used. (a) Yes (b) No Ans: b
769. In congested areas where excavation is expensive and inconvenient 'draw in system' of laying of underground cables is often adopted. (a) Yes (b) No Ans: a
770. Natural rubber is obtained from milky sap of tropical trees. (a) Yes (b) No Ans: a
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