ELECTRICIAN TRADE 1ST semisteritichatrapur.in/question/QB ELECTRICIAN MCQ 1ST SEM… · ·...

Industrial Training Institute, Chatrapur(Govt Of Odisha)

ELECTRICIAN TRADE 1 ST semister

1. The ratio of voltage and electric current in a closed circuit

a. remains constant b. varies c. increases d. falls

The curve representing ohm’s law is

a. sine function b. Linear c. a parabola d. a hyperbola

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

0 The resistance of wire varies inversely as

a. area of cross section b. length c. resistivity d. temperature

0 Which of the following quantities are same in all parts of a series circuit?

a. voltage b. power c. current d. resistance

0 Which of the following statements is false in case of a series circuit?

0 the voltage drop across each resister is same

1 the current flowing through each resistor is the same

c. applied voltage is equal to the sum of voltage drops across individual resistors resistorsare additive

1 A resistance of 30 Ω is connected across 240v supply. If a resistance R Ω is connected in parallel with 30Ω resistor across the same supply, the current drawn becomes triple of original one The unknown resistor R is

a. 15Ω b. 10Ω c. 5Ω d.30Ω

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

9. . Which of the following is not correct?


a. P=V/R^2 b. P=VI c. I=√(P/R) d. V=√PR

10. 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. decreas c. remain the sam

11. The voltage applied across an electric iron is halved. The power consumption of the iron will be:

a. one-halfthree-fourth b. one-fourth c. 1/√2times

12. Resistance of 200w,250v lamp will be

a. 625 Ω b. 1250Ω c.312.5Ω d.31.25Ω

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

14. A 200w, 100v lamp is to be operated on 250v supply. The additional resistance required to be connected in series will be:

a. 125Ω b. 50Ω c. 75Ω d.25Ω

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

16. KCL is applicable only to

a. electric circuits b. electronic circuits

c. junctions in a network d. closed loop in a network

17. KVL is concerned with

a. IR drop b. battery emf c. junction node d. both a and b

18. A wye arrangement of resistances has each resistance of 3Ω, the equivalent delta arrangement will have each resistance of values.

a. 9Ω b. 6Ω c. 3Ω d. 1Ω


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 5Ω is connected in series . The current will drop to0.2A when the resistance is further increased by

a. 10Ω b. 15Ω c. 25Ω d

20. Cells are connected in series in order to increase the

a. current capacity b. life of the cells c. voltage rating

0 terminal voltage

0 Cells are connected in parallel in order to increase

a. life of the cells b. efficiency c. current capacity d. voltage rating

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

23.The capacity of a battery is expressed in

a. amperes b. amperes-hour c. watts d. watt-hour

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

25. which one is classified as integrating instrument?

a. D’arsonval galvanometer b. ampere-hour meter c. ohm-meter d. ammeter 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

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

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

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

30. The S.I. unit of power isa. henry b. coulomb c. watt d. watt-hour31. Electric pressure is also calleda. resistance b. power c. voltage d. energy32 The substances whfch have a large number of free electrons and offer a low resistance are called

a. insulators b. inductors c. semi-conductorsd. conductors

33. Out of the following which is not a poor conductor ?a. Cast iron b. Copper c. Carbon d. Tungsten34. Out of the following which is an insulating material ?

a. Copperb. Gold c. Silver d. Paper

35. The property of a conductor due to which it passes current is calleda. resistance b. reluctance

c. conductance

d. inductance

36 . Conductance is reciprocal of(a) resistance

(b) inductance

(c) reluctance

(d) capacitance

37. The resistance of a conductor varies inversely as

(a) length(b) area of cross-section (c) temperature

(d) resistivity

38. With rise in temperature the resistance of pure metals

(a) Increases(b) decreases

(c) first increases and then decreases (d) remains constant39. With rise in temperature the resistance of semi-conductors(a) decreases (b) increases(c) first increases and then decreases

(d) remains constant


40. The resistance of a copper wire 200 m long is 21 Q. If its thickness (diameter) is0.44 mm, its specificresistance 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-m41. 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

42. An instrument which detects electric current is known as

(a) voltmeter (b) rheostat(c) wattmeter (d) galvanometer

43. In a circuit a 33 Q resistor carries a current of 2 A. The voltage across theresistor is(a) 33 V (b) 66 v

(c) 80V (d) 132 V

44. A light bulb draws 300 mA when the voltage across it is 240 V. The resistance ofthe light bulb is(a) 400 Q (b) 600 Q (c) 800 Q (d) 1000 Q45. 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 Q (b) 36 Q (c) 48 Q(d) 64 Q

46. Four wires of same material, the same cross-sectional area and the same lengthwhen connected in parallel give a resistance of 0.25 Q. If the same four wires are connected is series the effective resistancewill be(a) 1 Q (b) 2 Q (c) 3 Q (d) 4 Q47. A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohmsrespectively. 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 A48. 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 ^.s/m (d) nearly 3 x 108 m/s49. Which of the following material has nearly zero temperature co-efficient of resistance?(a) Manganin (b) Porcelain (c) Carbon (d) Copper50. You have to replace 1500 Q resistor in radio. You have no 1500 Q resistor but have several 1000 Q ones which you would connect

(a) two in parallel(b) two in parallel and one in series

(c) three in parallel

(d) three in

series51. 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.

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

53. Which of the following materials has a negative temperature co-efficient of resistance?

(a) Copper(b) Aluminum (c) Carbon (d) Brass

54. Ohm's law is not applicable to

(a) vacuum tubes(b) carbon resistors

(c) high voltage circuits (d) circuits with low current densities55. Which is the best conductor of


electricity ?(a) Iron (b) Silver (c) Copper (d) Carbon56. For which of the following 'ampere second' could be the unit ?(a) Reluctance (b) Charge (c) Power (d) Energy57. All of the following are equivalent to watt except

(a) (amperes) ohm(b) joules/sec.

(c) amperes x volts (d) amperes/volt

58. A resistance having rating 10 ohms, 10W is likely to be a0 metallic resistor1 carbon resistor2 wire wound resistor3 variable resistor0 Which one of the following does not have negative temperature co-efficient ?(a) Aluminium(b) Paper(c) Rubber(d) Mica1 Varistors are0 insulators0 non-linear

resistors

0 carbon resistors1 resistors with zero temperaturecoefficient 61. Insulating materialshave the function of0 preventing a short circuit between conducting wires1 preventing an open circuit between the voltage source and the

load2 conducting very large currents3 storing very high currents0 The rating of a fuse wire is always expressed in(a) ampere-hours(b) ampere-volts(c) kWh(d) amperes1 The minimum charge on an ion is0 equal to the atomic number of the atom1 equal to the charge of an electron2 equal to the charge of the number of electrons in anatom (#) zero 64. In a series circuit with unequalresistances0 the highest resistance has the most of the current through it1 the lowest resistance has the highest voltage drop2 the lowest resistance has the highest current3 the highest resistance has the highest voltage drop0 The filament of an electric bulb is made of(a) carbon(b) aluminium(c) tungsten(d) nickel1 A 3 Q resistor having 2 A current will dissipate the power of(a) 2 watts(b) 4 watts(c) 6 watts(d) 8 watts2 Which of the following statement is true?0 A galvanometer with low resistance in parallel is a voltmeter1 A galvanometer with high resis¬tance in parallel is a voltmeter2 A galvanometer with low resistance in series is an ammeter3 A galvanometer with high resis¬tance in series is an ammeter0 The resistance of a few metres of wire conductor in closed electrical

circuit is(a) practically zero(b) low(c) high (d) very high1 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 branch0 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 ohm1 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

0 rest of the two bulbs will not light1 all three bulbs will light2 the other two bulbs will light0 The four bulbs of 40 W each are connected in series wifti a battery acrossthem, 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 above1 Two resistances Rl and Ri are connected in series across the voltage sourcewhere R2>Ri. The largest dropwill be across(a) R2(b) Ri(c) either Rl or Rz(d) none of them2 What will be energy used by the battery if the battery has to drive 6.28 x1018 electrons with potential difference of 20 V across the terminal ?(a) 5 joules(b) 10 joules(c) 15 joules(d) 20 joules3 A closed switch has a resistance of0 zero1 about 50 ohms2 about 500 ohms3 infinity76. The hot resistance of the bulb's fila¬ment is higher than its cold resistance because the temperature co-efficient of the filament is0 zero1 negative2 positive3 about 2 ohms per degree0 Heat in a conductor is produced on the passage of electric current due to(a) reactance(b) capacitance(c) impedance(d) resistance1 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

The thickness of insulation provided on the conductor depends on(a) the magnitude of voltage on the con-ductor(b) the magnitude of current flowing through it(c) both (a) and (b)(d) none of the aboveWhich of the following quantities remain the same in all parts of a series circuit ?(a) Voltage

0 Current1 Power2 Resistance81. 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 will0 decrease1 increase2 remain same3 heater will burn out82. In an electric kettle water boils in 10m minutes. It is required to boil the boiler in 15 minutes, using same supply mains0 length of heating element should be decreased1 length of heating element should be increased2 length of heating element has no effect on heating if water3 none of the above83. An electric filament bulb can be worked from0 D.C. supply only1 A.C. supply only2 Battery supply only3 All above84. Resistance of a tungsten as applied voltage increases0 decreases1 increases2 remains same3 none of the above85. Electric current passing through the circuit produces0 magnetic effect1 luminous effect2 thermal effect3 chemical effect4 all above effects86. Resistance of a material always decreases if0 temperature of material is decreasedtemperature of material is increased0 number of free electrons available become more1 none of the above is correctAns: c87. 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 inputAns: b88. When electric current passes through a metallic conductor, its temperature rises. This is due to23 collisions between conduction electrons and atoms24the release of conduction electrons from parent atoms0 mutual collisions between metal atoms1 mutual collisions between conductingelectrons Ans: a89. Two bulbs of 500 W and 200 W rated at 250 V will have resistance ratio as

234 : 252425 : 425 2 : 5265 :2 Ans:c90. A glass rod when rubbed with silk cloth is charged because0 it takes in proton1 its atoms are removed2 it gives away electrons3 it gives away positivecharge Ans: c91. Whether circuit may be AC. or D.C. one, following is most effective in reducingthe magnitude of the current.0 Reactor1 Capacitor2 Inductor3 Resistor Ans: d92. It becomes more difficult to remove0 any electron from the(6) first electron from the orbit0 second electron from the orbit1 third electron from theorbit Ans: d0 When one leg of parallel circuit is opened out the total current will(a) reduce(b) increase(c) decrease(d) becomezero Ans: c1 In a lamp load when more than one lamp are switched on the total resistance of

the load0 increases1 decreases2 remains same3 none of theabove Ans: b95. Two lamps 100 W and 40 W are connected in series across230 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: bResistance of 220 V, 100 W lamp will be(a) 4.84 Q(b) 48.4 Q(c) 484 ft(d) 4840Q Ans: cIn the case of direct current

0 magnitude and direction of current remains constant1 magnitude and direction of current changes with time2 magnitude of current changes with time3 magnitude of current remains con¬stantAns: a98. When electric current passes through a bucket full of water, lot of bubbling is observed. This suggests that the type of supply is23 A.C.24 D.C.25 any of above two26none of theabove Ans: b99. Resistance of carbon filament lamp as the applied voltage increases.23 increases24 decreases25 remains same26none of theabove Ans: b100. Bulbs in street lighting are all connected in0 parallel1 series2 series-parallel3 end-to-end Ans: a101. For testing appliances, the wattage of test lamp should be0 very low1 low2 high3 anyvalue Ans:c102. Switching of a lamp in house produces noise in the radio. This is becauseswitching operationproduces23 arcs across separating contacts24 mechanical noise of high intensity25 both mechanical noise and arc be¬tween contacts26none of the aboveAns: a103. 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 involume, 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 willdecreaseincrease

0 remain constant1 none of theabove Ans: b106. A field of force can exist only between0 two molecules1 two ions2 two atoms3 two metalparticles Ans: b107. A substance whose molecules consist of dissimilar atoms is calledsemi-conductorsuper-conductocompoundinsulatorAns: c0 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 ofwire Ans: a1 Three identical resistors are first connected in parallel andthen in series. The resultant resistance of the first combinationto the second will be(a) 9 times(b) 1/9 times(c) 1/3 times(d) 3timesAns: b2 Which method can be used for absolute measurement of resistances ?(a) Lorentz method(b) Releigh method(c) Ohm's law method(d) Wheatstone bridgemethod Ans: d3 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: c112. Ohm's law is not applicable to

(a) semi-conductors(b) D.C. circuits

(c) small resistors (d) high currentsAns: a113. 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

0 160 ohms1 80 ohms2 20 ohms

0 10ohmsAns: d114. A nichrome wire used as a heater coil has the resistance of 2 £2/m. For aheater of 1 kW at 200 V, the length of wire required will be2380 m2460 m25 40 m2620mAns: a115. Temperature co-efficient of resistance is expressed in terms of0 ohms/°C1 mhos/ohm°C0 ohms/ohm°C(d) mhos/°C Ans: c0 Which of the following materials has the least resistivity ?(a) Zinc(b) Lead(c) Mercury(d)CopperAns:1 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 in¬sulation layer(c) resistance of heater coil is more than the supply wires(d) supply wires are made of superiormaterial Ans: c2 The condition for the validity under Ohm's law is that0 resistance must be uniform1 current should be proportional to the size of the resistance2 resistance must be wire wound type3 temperature at positive end should be more than the temperatureat negative end Ans: a119. Which of the following statement is correct ?A semi-conductor is a material whose conductivity is same as be¬tween that of aconductor and an insulatorA semi-conductor is a material which has conductivity having average value ofconductivity of metal and insulator0 A semi-conductor is one which con¬ducts only half of the applied voltage1 A semi-conductor is a material made of alternate layers of conductingmaterial and insulator Ans: a120. A rheostat differs from potentiometer in the respect that it0 has lower wantage rating1 has higher wattage rating2 has large number of turns3 offers large number oftappings Ans: b

121. The weight of an aluminium conductor as compared to a copper conductor ofidentical cross-

section, for the same electrical resistance, is Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 50% Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 60% Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ2 100% Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ3150%Ans: a122. An open resistor, when checked with an ohm-meter reads0 zero1 infinite2 high but within tolerance3 low but not zeroAns: b123. are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.0 Varistors1 Thermistor2 Semi-conductors3 Variableresistors Ans: c124. All good conductors have high0 conductance1 resistance2 reluctance3 thermalconductivity Ans: a125. Voltage dependent resistors are usually made from0 charcoal12 nichrome3 graphite Ans: c126. Voltage dependent resistors are used0 for inductive circuits(6) to supress surges0 as heating elements1 as currentstabilizers Ans: b127. The ratio of mass of proton to that of electron is nearly

(a) 1840 (b) 1840 (c) 30(d) 4

Ans: a0 The number of electrons in the outer most orbit of carbon atom is(a) 3(b) 4(c) 6(d) 7Ans: b1 With three resistances connected in parallel, if each dissipates 20 W the totalpower supplied by the voltage source equals

Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀԀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 10 W Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀԀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 20 W Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀԀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ2 40 W Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀЀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀԀЀȀ Ā⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ360 WAns: d130. A thermistor has0 positive temperature coefficient1 negative temperature coefficient2 zero temperature coefficient3 variable temperaturecoefficient Ans: c131. If/, R and t are the current, resistance and time respectively, thenaccording to Joule's law heat produced will be proportional to0 I2Rt1 I2Rf2 I2R2t3 I2R2t* Ans: a132. Nichrome wire is an alloy of0 lead and zinc1 chromium and vanadium2 nickel and chromium3 copper andsilver Ans: c133. When a voltage of one volt is applied, a circuit allows one microampere current to flow through it. The conductance of the circuit is23 1 n-mho24 106 mho25 1 milli-mho26 none of theabove Ans: a

0 Which of the following can have negative temperature coefficient ?(a) Compounds of silver(6) Liquid metals(c) Metallic alloys(d)ElectrolytesAns: d

1 Conductance : mho ::0 resistance : ohm1 capacitance : henry2 inductance : farad3 lumen :steradian Ans: a136. 1 angstrom is equal to2310-8 mm(6) 10"6 cm23 10"10 m

(d) 10~14 m Ans: c768One newton metre is same as(a) one watt(b) one joule(c) five joules(d) one joulesecond Ans: b769The force between two charges is 120 N. If the distance between the chargesis doubled, the force will be(a) 60 N(b) 30 N(c) 40 N(d) 15 NAns: b770The electric field intensity at a point situated 4 metres from a point charge is 200N/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/CAns: c0 The lines of force due to charged particles are(a) always straight(b) always curved(c) sometimes curved(d) none of the aboveAns: b1 The electric field at a point situated at a distance d from straightcharged conductor is(a) proportional to d(b) inversely proportional to d(c) inversely proportional to d(d) none of the aboveAns: b2 The direction of electric field due +0 positive charge is .(a) away from the charge (b) towards the charge0 both (a) and (b) (d) none of the aboveAns: a143. A field line and an equipotential surface are0 always parallel(b) always at 90°0 inclined at any angle 0(d) none of the aboveAns: b144. The ability of charged bodies to exert force on 6ne another is attributed to the existence of0 electrons1 protons2 neutrons3 electric fieldAns: d

145. If the sheet of a bakelite is inserted between the of an , the capacitancewill(a) decrease(b) increase(c) remains unchanged(d) become zeroAns: b

146. A capacitor stores 0.24 coulombs at 10 volts. Its capacitance is0 0.024 F1 0.12 F2 0.6 F3 0.8 FAns: a147. For making a capacitor, it is better to select a dielectric having0 low permittivity1 high permittivity2 permittivity same as that of air3 permittivity slightly more than that of airAns: b148. The units of capacitance are0 volts/coulomb1 coulombs/volt2 ohms3 henry/WbAns: b149. If three 15 uF capacitors are connected in series, the net capacitance is0 5 uF(6) 30 uF0 45 uF1 50 uFAns: a150. If three 10 uF capacitors are connected in parallel, the net cararitance is0 20 uF1 30 uE2 40 uF3 50 uFAns: b151. A dielectric material must be0 resistor1 insulator2 good conductor3 semi conductorAns: b

152. An electrolytic capacitor can be used for

D.C. onlyAC. onlyboth D.C. as well as A.C.Ans: a153. The capacitance of a capacitor is not affected by0 distance between plates(6) area of plates0thickness of plates1all of the aboveAns: c154. Which of the following is not a vector ?0 Linear momentum1 Angular momentum2 Electric field3 Electric potentialAns: b155. Two plates of a parallel capacitor after being charged from a constant voltage source are separated apart by means of insulated handles, then theᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ대Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ4 Voltage across the platesᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ대Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ5 voltage across the plates

decreasesᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ대Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ6 charge on the capacitor

decreasesᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ대Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ7 chargeon the capacitor increases Ans: b156. If A.C. voltage is applied to capacitive circuit, the alternating current can flow in the circuitbecause0 varying voltage produces the charg¬ing and dicharging currents5888 of high peak value5889 charging current can flow5890 discharge current can flowAns: a157. Voltage applied across a ceramic dielectric produces an electrolytic field 100 times greaterthan air. What will be the value of dielectric constant ?0 50(6) 1000 1501 200Ans: b158. Which of the following statements is correct ?(a) Air capacitors have a blackband to indicate the outside foil(6) Electrolytic capacitor must be con¬nected in the correct polarity1024 Ceramic capacitors must be con¬nected in the correct polarity1025 Mica capacitors are available in capacitance value of 1 to10 pF Ans: b159. The dissipation factor of a good dielectric is of the order of

0 0.00021 0.002

5888 0.0258890.2Ans: a160. "The total electric flux through any closed surface surrounding charges is equal to theamount oflcharge enclosed".The above statement is associated with0 Coulomb's square law1 Gauss's law2 Maxwell's first law3 Maxwell's second lawAns: b161. Three capacitors each of the capacity C are given. The resultant capacity 2/3 Ccan be obtained by using them0 all in series1 all in parallel2 two in parallel and third in series with this combination3 two in series and third in parallel across this combinationAns: c162. For which of the following parameter variation, the capacitance of the capacitorremains unaffected ?5888 Distance between plates5889 Area of the plates5890 Nature of dielectric5891 Thickness of theplates Ans: d163. Which of the following statement is true ?0 The current in the discharging capacitor grows linearly1 The current in the dicharging capacitor grows exponentially2 The current in the discharging capacitor decays exponentially3 The current in the discharging capacitor decreases constantlyAns: b164. Which of the following expression is correct for electric field strength ?0 E = D/E1 E = D2/t2 E = jtD3 E= nD2Ans: a165. In a capacitor the electric charge is stored inᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ256 metal platesᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ257 dielectricᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ258 both (a) and (6)ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ259none of the aboveAns: b

166. Which of the following materials has the highest value of dielectric constant?0 Glass1 Vacuum

0 Ceramics1 OilAns: c23 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 aboveAns: c24 Which of the following statements is incorrect ?0 The leakage resistance of ceramic capacitors is generally high1 The stored energy in a capacitor decreases with reduction in value of capacitance2 The stored energy in a capacitor increases with applied voltage3 A wire cable has distributed capacitance between the conductorsAns: b0 Which of the following capacitors has relatively shorter shelf life ?(a) Mica capacitor(b) Electrolytic capacitor(c) Ceramic capacitor(d) Paper capacitorAns: b1 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 aboveAns: a2 In the case of a lossy capacitor, its series equivalent resistance value will be(a) small(b) very small(c) large(d) zeroAns: c3 The power dissipated in a pure capacitor is(a) zero(6) proportional to applied voltage23 proportional to value of capacitance24 both (b) and (c) aboveAns: a173. In a capacitive circuit0 a steady value of applied voltage causes discharge1 an increase in applied voltage makes a capacitor charge2 decrease in applied voltage makes a capacitor charge3 none of the aboveAns: b174. When a dielectric slab is introduced in a parallel plate capacitor, the potential difference

between plates will0 remain uncharged1 decrease2 increase3 become zeroAns: b175. Capacitance increases with23 increase in plate area and decrease in distance between the plates24 increase in plate area and distance between the plates25 decrease in plate area and value of applied voltage26 reduction in plate area and distance between the platesAns: a176. A capacitor consists of23 two insulators separated by a con¬ductor24 two conductors separated by an in¬sulator25 two insulators only26 two conductors onlyAns: b177. A paper capacitor is usually available in the form oftubesrolled foildiscmeshed platesAns: b178. Air capacitors are generally available in the range0 10 to 400 pF1 1 to 20 pF2 100 to 900 pF3 20 to 100 pFAns: a

The unit of capacitance is(a) henry(b) ohm(c) farad(d) farad/mAns: cA 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 uFAns: bA capacitor in a circuit became hot and ultimately exploded due to wrong con¬nections,which type of capacitor it could be ?(a) Paper capacitor

0 Ceramic capacitor1 Electrolytic capacitor2 Any-of the aboveAns: c182. Energy stored in the electric field of a capacitor C when charged from a D.C source ofvoltage V is equal to joules0 CV21 C2V2 CV23 CVAns: a183. The absolute permittivity of free space is given by0 8.854 x 1(T9 F/m)(6) 8.854 x 1(T10 F/m)0 8.854 x KT11 F/m1 8.854 x 10"12 F/mAns: b184. The relative permittivity of free space is given by0 11 102 1003 1000Ans: a185. Electric field intensity is a quantity0 scalar1 vector2 both (a) and (6)3 none of the aboveAns: b186. When 4 volts e.m.f. is applied across a 1 farad capacitor, it will store energy of0 2 joules1 4 joules2 6 joules3 8 joulesAns: d187. The capacitor preferred for high circuits is0 air capacitor1 mica capacitor2 electrolytic capacitor3 none of the aboveAns: b188. The capacity of capacitor bank used in power factor correction is expressed in terms of0 kW1 kVA2 kVAR3 volts

Ans: c0 While testing a capacitor with ohm-metre, if the capacitor shows charging, but the finalresistance reading is appreciably less than normal, it can be concluded that the capacitor is(a) short-circuited(b) open circuited(c) alright(d) leakyAns: d1 If a 6 (iF capacitor is charged to 200 V, the charge in coulombs will be0 800 uC1 900 uC2 1200 uC3 1600 uCAns: c191. Which capacitor will be physically smaller for the same ratings ?0 Ceramic capacitor1 Paper capacitor2 Both will be of equal size3 None of the aboveAns: a192. What is the value of capacitance that must be connected in parallel with 50 pF condenser tomake an equivalent capacitance of 150 pF ?0 50 pF1 100 pF2 150 pF3 200 pFAns: b193. A mica capacitor and a ceramic capacitor both have the same physical dimensions. Whichwill have more value of capacitance ?5888 Ceramic capacitor5889 Mica capacitor5890 Both will have identical value of capacitance5891 It depends on appliedvoltage Ans: a194. Which of the following material has least value of dielectric constant ?0 Ceramics1 Oil2 Glass3 PaperAns: b195. Which of the following capacitors will have the least value of breakdown voltage ?0 Mica1 Paper2 Ceramic3 ElectrolyticAns: d

196. The breakdown voltage for paper capacitors is usually1024 20 to 60 volts1025 200 to 1600 volts1026 2000 to 3000 volts1027 more than 10000volts Ans:0 Dielectric constant for mica is nearly(a) 200(b) 100(c) 3 to 8(d) 1 to 2Ans: c1 The value of dielectric constant for vacuum is taken as(a) zero(b) 1(c) 4(d) 10Ans: b

2 Which of the following capacitors is marked for polarity ?(a) Air(b) Paper(c) Mica(d) ElectrolyticAns: d3 Which of the following capacitors can be used for temperature compensation ?(a) Air capacitor(b) Ceramic capacitor(c) Paper capacitor(d) None of the aboveAns: b4 Which of the following statements is incorrect ?5888 The thinner the dielectric, the more the capacitance and the lower the voltagebreakdown rating for a capacitor .5889 A six dot mica capacitor colour coded white, green, black, red and yellow has thecapacitance value of 500 pF5890 Capacitors in series provide less capacitance but a higher voltage breakdown ratingfor the combina¬tion5891 A capacitor can store charge be¬cause it has a dielectric between two conductorsAns: b202. Paper capacitors usually have a tolerance of0 ± 5%1 ± 10%2 ± 15%3 ± 20%Ans: b

0 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 aboveAns: b1 The electrostatic force between two charges of one coulomb each and placed at a distance of0.5 m will be(a) 36 x 10fa(b) 36 x 107 N(c) 36 x 108 N(d) 36 x 109 NAns: d2 The units of volume charge density are0 Coulomb/metre1 Coulomb/metre2 Coulomb/metre3 Coulomb/metreAns: c206. "The surface integral of the normal component of the electric displacement D over anyclosed surface equals the charge enclosed by the surface".The above statement is associated with0 Gauss's law1 Kirchhoff s law0 's law1 Lenz's lawAns: a207. Dielectric strength of mica is0 10 to 20 kV/mm(6) 30 to 50 kV/mm0 50 to 200 kV/mm1 300 to 500 kV/mmAns: c208. The dielectric constant (relative permittivity) of glass is given by0 0.1 to 0.41 0.5 to 1.0(c) 2.0 to 4.0 (d) 5 to 100Ans: d209 capacitors are mainly used for radio frequency tuning.0 Paper1 Air2 Mica3 ElectrolyticAns: b210. capacitors can be used only for D.C.ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 Air

ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 Paper

(e) Mica(d) ElectrolyticAns: d0 capacitors are used in transistor circuits.(a) Ceramic(b) Paper(c) Air(d) ElectrolyticAns: a1 capacitors are used for audio frequency and radio frequency coupling and tuning.(a) Air(b) Mica(c) Plastic film(d) CeramicAns: b2 The inverse of capacitance is called0 reluctance1 conductance2 susceptance3 elastanceAns: d214. When the dielectric is homogeneous,the potential gradient is0 uniform1 non-uniform2 zero3 any of the aboveAns: a215. The potential gradient across the material of low permittivity is than across the material ofhigh permittivity.0 smaller1 greater2 both (a) and (b)3 none of the aboveAns: b216. ________field is associated with the capacitor.0 Electric1 Magnetic2 Both (a) and (b)3 None of the aboveAns: a217. A capacitor having capacitance of 5 uF is charged to a potential difference of 10,000 V. Theenergy stored in the capacitor is0 50 joules1 150 joules2 200 joules

(d) 250 joulesAns: dЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 A single core cable used on 33000 V hasconductor diameter 10 mm and the in¬ternal diameter of sheath 25 mm. The maximumelectrostatic 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/mAns: bЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 Two infinite parallel plates 10 mmapart have maintained between them a potential difference of 100 V. The acceleration ofan 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/s2Ans: dЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ2 The total deficiency or excess of electrons in a body is

known as0 current1 voltage2 potential gradient3 chargeAns: d0 The relative permittivity has the following units(a) F/m(b) m/F(c) Wb/m(d) no unitsAns: c1 The phenomenon of an uncharged body getting charged merely by the nearness of a chargedbody is known as(a) pholoelectric effect(b) chemical effect(c) magnetic effect(d) inductionAns: d2 A unit tube of flux is known as tube0 Newton1 Faraday2 Michale3 None of the aboveAns: b

224. The number of Faraday tubes of flux passing through a surface in an electric field is called0 electric flux(6) electric flux density5888 magnetic flux density5889 electric charge density

Ans: aThe unit of electric instensity is(a) N/C2(b) Wb/m2(c) N/C(d) N2/CAns: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 aboveAns: cat a point may be defined as equal to the lines of force passing normally through a unit crosssection at that point.(a) Electric intensity(6) Magnetic flux density0 Electric flux1 None of the aboveAns: a228. Electric intensity at any point in an electric field is equal to the at that point.0electric flux1magnetic flux density2potential gradient3none of the aboveAns: c229. Electric displacement is a______quantity.0 scalari vectorii both of the aboveiii none of the aboveAns: b230. at a point is equal to the negative potential gradient at that point.0 Electric intensity(6) Electric flux0 Magnetic flux1 Magnetic flux densityAns: a231. The unit of dielectric strength is given by0 V/m1 V2/m2 m/V3 m/V2Ans: a232. Dielectric strength ______ with increasing thicknessЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 increases

0 decreases1 remains unaltered2 none of the aboveAns: b233. The property of a capacitor to store electricity is called its0 capacitance1 charge2 energy3 none of the aboveAns: a234.___ is that property of a capacitor which delays any change of voltage across it.0 Inductance1 Capacitance2 Potential gradient3 None of the aboveAns: b235. A capacitance of 100 fiF is connected in series with a resistance of 8000 £2. The timeconstant of the circuit is0 0.2 s1 0.4 s2 0.6 s3 0.8 sAns: d236. In a cable capacitor, voltage gradient ismaximum at the surface of the0 earth1 conduction2 sheath3 insulatorAns: b237. The time constant of an R-C circuit is defined as the time during which capacitor chargingvoltage actually rises to ______ percent of its______value.0 37, initial1 63.2, initial2 63.2, final3 37, finalAns: c238. The time constant and R-C circuit may also be defined as the time during which the chargingcurrent falls to ______ percent of its initial maximum value,ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ嬀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 37ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ嬀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 42ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ嬀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ2 63

Ѐ Ā⤀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ嬀Ā ᜀĀȀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ĀȀȀ⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ĀȀȀ⤀ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ373Ans: a239. The capacitance of a capacitor is influenced by0 plate area1 plate separation

0 nature of dielectric1 none of the above2 all of the aboveAns:240. A capacitor consists of two0 ceramic plates and one mica disc1 insulators separated by a dielectric2 silver-coated insulators3 conductors separated by an insulatorAns: d241. Permittivity is expressed in0 Farad/sq-m1 Farad/metre2 Weber/metre3 Weber/sq-mAns: b242. Dielectric strength of a material depends on0 moisture content1 temperature2 thickness3 all of the above4 none of the aboveAns: d243. What will happen to an insulating medium if voltage more than the breakdown voltage isapplied on it ?0 It will become magnetic1 It will melt2 It will get punctured or cracked3 Its molecular structure will get changedAns: c244. Which medium has the least dielectric strength ?ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ渀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 Paraffin waxЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ渀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 QuartzЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ渀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀ2 Glass

ЀᜀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ渀Ā ĀȀ⸀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ3AirAns: d245. 1 volt/metre is same as0 1 metre/coulomb(6) 1 newton metre(c) 1 newton/metre(d) 1 joule/coulombAns: c246. One volt is the same as0 one joule/coulomb1 one coulomb/joule2 one coulomb3 one jouleAns: a247. The capacitance between two plates increases with

0 shorter plate area and higher ap¬plied voltage(6) shorter plate area and shorter dis¬tance between them0 larger plate area, longer distance between plates and higher,applied voltage1 larger plate area and shorter distance between platesAns: d0 The capacitance C is charged through a resistance R. The time constant of the chargingcircuit is given by(a) CIR(b) 1/RC(c) RC(d) RICAns: c1 The bridge used for the measurement of the value of the capacitance is0 Wien's bridge1 Wheatstone bridgeᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀ ᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ0 Schering bridgeᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀЀЀ ᜀᜀĀȀȀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀĀᜀ1 Hay's bridge Ans:c250. If an ohmmeter reading immediately goes practically to zero and stays there, capacitor is0 charged1 short-circuited2 lossy3 satisfactoryAns: b251. Out of the following capacitors of identical rating which one will have the smallestdimensions ?0 Aluminium foil capacitor1 Mica capacitor2 Ceramic capacitor3 Paper capacitorAns: c252. An uncharged conductor is placed near a charged conductor, then23 the uncharged conductor gets charged by conduction(6) the uncharged conductor gets charged by induction and then attracted towards the charging body23 the uncharged conductor is attracted first and then charged by induction24 it remains as suchAns: b0 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 aboveAns: b1 Paper condenser is(a) always polarised

(6) usually of fixed value0 electrolytic condenser1 a variable condenserAns: b255. Mica capacitors are characterised by all of thte following except0 stable operation1 accurate value2 low leakage reactance3 low lossesAns: c256. A potential of 400 V is applied to a capacitor, the plates of which are 4 mm apart. Thestrength of electric field is0 100 kV/m1 10 kV/m2 5 kV/m3 2 kV/mAns: a257. For a good 0.05 uF capacitor ohmmeter reading should0 show low resistance momentarily and back off to a very high resis¬tance(6) show high resistance momentarily and then a very low resistance0 go quickly to 50 ohm approximately and remain there1 not move at allAns: aThe ohmmeter reading for a short circuited capacitor is(a) infinity(b) few kilo ohms(c) few megaahms(d) zeroAns: dWhich of the following statements is correct ?0 Mica capacitors are available in capacitance values of 5 to 20 \iF1 Air capapitors have a black band to indicate the outside foil2 Electrolytic capacitors must be connected in correct polarity3 Ceramic capacitors must be con¬nected in correct polarityAns: c260. 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

An electrolytic capacitor is generally made to provide(a) low capacitance(b) fixed capacitance(c) variable capacitance(d) large value of capacitanceAns: dIn order to remove static electricity from machinery(a) construct insulated cabins

insulate the machineryground the frameworkhumidify the surroundingsAns: c263. If a third equal and similar charge is placed between two equal and similar charges, then thisthird charge willmove out of the field of influence of the two chargesremain in stable equilibriumnot be in equilibriumbe in unstable equilibriumAns: b264. A region around a stationary electric charge hasan electric fielda magnetic fieldboth (a) and (b)none of the aboveAns: a265. The minimum value of potential gradient in a cable occurs ininsulationconductorouter sheathuniformly all overAns: a266. Dielectric strength of mediumincreases with rise in temperatureincreases with moisture contentis same for all insulating materialsnone of the aboveAns: dAcharge which when placed in vacuum from an equal and similar charge repels with a force of 9x 10 N, is known as(a) milli-coulomb(b) micro-coulomb(c) pico-coulomb(d) coulombAns: bDielectric strength of a medium is usually expressed in(a) J/mm (b) C/m2 (c) kV/mm (d) N/mmAns: c269. A positive and a negative charge are initially 50 mm apart. When they are moved closetogether so that they are now only 10 mm apart, the force between them will be5 times smaller than before5 times greater than before10 times greater than before25 times larger than beforeAns: d

Which is the most superior dielectric out of the following ?(a) Air(b) Glass(c) Bakelite(d) PaperAns: cWhen a dielectric is placed in an electric field the field strength(a) decreases(b) increases(c) reduces to zero(d) remain unchangedAns: aTo 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 surfaceAns: bWhich of the following capacitor is preferred in case of single phase motor ?(a) Mica capacitor(b) Paper capacitor(c) Electrolytic capacitor(d) Ceramic capacitorAns: cA capacitance is a circuit component that opposes the change in circuitcurrentvoltageimpedancenone of the aboveAns: a275. A condenser suitable for D.C. only ismetallic plate variable gang condensermetallic paper capacitoroil impregrated paper condenserpoled aluminium electrolytic condenserAns: d276. 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 aboveAns: b277. An air gap is usually inserted in magnetic circuits toincrease m.m.f.increase the fluxprevent saturationnone of the aboveAns: c

278. The relative permeability of a ferromagnetic material isless than onemore than onemore than 10more than 100 or 1000Ans: d279. The unit of magnetic flux ishenryweberampereturn/weberampere/metreAns: b280. Permeability in a magnetic circuit corresponds to______ in an electric circuit.resistanceresistivityconductivityconductanceAns: c281. Point out the wrong statement.Magnetic leakage is undesirable in electric machines because itlowers their power efficiencyincreases their cost ofleads to their increased weightproduces fringingAns: a282. Relative permeability of vacuum is11 H/m1/4JI4n x 10-' H/mAns: a283. Permanent magnets are normally made ofalnico alloysaluminiumcast ironwrought ironAns: a

Energy stored by a coil is doubled when its current is increased by percent.(a) 25(b) 50 (c)41.4(d) 100Ans: cThose magnetic materials are best suited for making armature and transformer cores whichhave____permeability and_______hystersis loss.

high, highlow, highhigh, lowlow, lowAns: c286. The rate of rise of current through an inductive coil is maximumat 63.2% of its maximum steady valueat the start of the current flowafter one time constantnear the final maximum value of currentAns: b287. When both the inductance and resistance of a coil are doubled the value oftime constant remains unchangedinitial rate of rise of current is doubledfinal steady current is doubledtime constant is halvedAns: a288. The initial rate of rise of current through a coil of inductance 10 H when suddenly connectedto a D.C. supply of 200 V is_______Vs50200.05500Ans: b289. A material for good magnetic memorylow hysteresis losshigh permeabilitylow retentivityhigh retentivityAns: d290. Conductivity is analogous toretentivityresistivitypermeabilityinductanceAns: c291. 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 retentivityAns: d292. Those materials are well suited for making permanent magnets which have______retentivityand _______coercivity.low, highhigh, highhigh, lowlow, low

Ans: b293. If the area of hysteresis loop of a material is , the hysteresis loss in this material will bezerosmalllargenone of the aboveAns: c294. Hard steel is suitable for making permanent magnets becauseit has good residual magnetismits hysteresis loop has large areaits mechanical strength is highits mechanical strength is lowAns: a295. Silicon steel is used in electrical machines because it haslow co-ercivitylow retentivitylow hysteresis losshigh co-ercivityAns: c296. Conductance is analogous topermeancereluctancefluxinductanceAns: a297. The property of a material which opposes the creation of magnetic flux in it is known asreluctivitymagnetomotive forcepermeancereluctanceAns: d298. The unit of retentivity isweberweber/sq. mampere turn/metreampere turn

Ans: bReciprocal of reluctance is(a) reluctivity(b) permeance(c) permeability(d) susceptibilityAns: bWhile comparing magnetic and electric circuits, the flux of magnetic circuit iscompared with which parameter of electrical circuit ?E.m.f.

CurrentCurrent densityConductivityAns: b301. The unit of reluctance ismetre/henryhenry/metrehenry1/henryAns: d302. A ferrite core has less eddy current loss than an iron core becauseferrites have high resistanceferrites are magneticferrites have low permeabilityferrites have high hysteresisAns: d303. Hysteresis loss least depends on(a) volume of material (b) frequency(c) steinmetz co-efficient of material(d) ambient temperatureAns: dLaminated cores, in electrical machines, are used to reduce(a) copper loss(b) eddy current loss(c) hysteresis loss(d) all of theabove Ans: b"The mass of an ion liberated at an electrode is directly proportional to the quantity ofelectricity".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 lawAns: cThe charge required to liberate one gram equivalent of any substance is known as______ constant(a) time (b) Faraday's(c)Boltzman Ans: bDuring the charging of a lead-acid cellits voltageit gives out energyits cathode becomes dark chocolate brown in colourspecific gravity of H2SO4 decreasesAns: a308. The capacity of a lead-acid cell does not depend on its(a) temperature

rate of chargerate of dischargequantity of active materialAns: b309. During charging the specific gravity of the electrolyte of a lead-acid batteryincreasesdecreasesremains the samebecomes zeroAns: a

The active materials on the positive and negative plates of a fully chargedlead-acid battery arelead and lead peroxidelead sulphate and leadlead peroxide and leadnone of the aboveAns: c310. When a lead-acid battery is in fully charged condition, the colour of itspositive plate isdark greybrowndark brownnone of aboveAns: c311. The active materials of a nickel-iron battery arenickel hydroxidepowdered iron and its oxide(c) 21% solution of KOH (d) all of the aboveAns: dThe ratio of ampere-hour efficiency to watt-hour efficiency of a lead-acid cellis(a) just one(b) always greater than one(c) always less than one(d) none of theabove. Ans: bThe best indication about the state of charge on a lead-acid battery is givenby(a) output voltage(b) temperature of electrolyte(c) specific gravity of electrolyte(d) none of the aboveAns: cThe storage battery generally used in electric power station isnickel-cadmium batteryzinc-carbon battery

lead-acid batterynone of the aboveAns: c315. The output voltage of a charger isless than the battery voltagehigher than the battery voltagethe same as the battery voltagenone of the aboveAns: b316. Cells are connected in series in order toincrease the voltage rating(6) increase the current ratingincrease the life of the cellsnone of the aboveAns: aFive 2 V cells are connected in parallel. Theoutput voltage is(a) 1 V(6) 1.5 V(c) 1.75 V(d) 2 VAns: dThe capacity of a battery is expressed in terms ofcurrent ratingvoltage ratingampere-hour ratingnone of the aboveAns: c319. Duringthe charging and discharging of a nickel-iron cellcorrosive fumes are producedwater is neither formed nor absorbednickel hydroxide remains unsplitits e.m.f. remains constantAns: bAs compared to constant-current system, the constant-voltage system ofcharging 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 gassingAns: cA dead storage battery can be revived by(a) adding(6) adding so-called battery restorera dose of H2SO4none of the above

Ans: dAs compared to a lead-acid cell, the efficiency of a nickel-iron cell is less dueto its(a) compactness(b) lower e.m.f.(c) small quantity of electrolyte used(d) higher internal resistanceAns: dTrickle charging of a storage battery helps tomaintain proper electrolyte levelincrease its reserve capacityprevent sulphationkeep it fresh and fully chargedAns: d324. Those substances of the cell which take active part in chemical combinationand hence produce electricity duringcharging or discharging are known as______materials.(a) passive (b) active (c) redundant (d) inert Ans: b

In a lead-acid cell dilute sulphuric acid (electrolyte) approximatelycomprises 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 H2S04Ans: cIt is noticed that durmg chargingthere is a rise in voltageenergy is absorbed by the cellspecific gravity of H2SO4 is increasedthe anode becomes chocolate brown in colour (PbCfe) and cathode be¬comesgrey metallic lead (Pb)all of the aboveAns: e327. It is noticed that during discharging the following does not happenboth anode and cathode become PbS04specific gravity of H2SO4 decreasesvoltage of the cell decreasesthe cell absorbs energyAns: d328. The ampere-hour efficiency of a leadacid cell is normally between20 to 30%40 to 50%60 to 70%90 to 95%Ans: d

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 to95% Ans: cThe capacity of a lead-acid cell is measured inamperesampere-hourswattswatt-hoursAns: bThe 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 aboveAns: eWhen the lead-acid cell is fully charged, the electrolyte assumes _____appearance(a) dull(b) reddish(c) bright(d) milkyAns: dThe e.m.f. of an Edison cell, when fully charged, is nearly1.4 V1 V0.9 V0.8 VAns: a334. The internal resistance of an alkali cell is nearly _____ times that of the lead-acid cell.twothreefourfiveAns: d335. The average charging voltage for alkali cell is about1 V1.2 V1.7 V2.1 VAns: c336. On the average the ampere-hour efficiency of an Edison cell is about

40%60%70%80%Ans: d337. 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

Lead-acid cell has a life of nearly charges and discharges(a) 500(b) 700(c) 1000(d) 1250Ans: dLife of the Edison cell is at leastfive yearsseven yearseight yearsten yearsAns: a340. The internal resistance of a lead-acid cell is _____ that of Edison cellless thanmore thanequal tonone of the aboveAns: a341. Electrolyte used in an Edison cell isNaOHKOHHC1HN03Ans: b342. Electrolyte used in a lead-acid cell isNaOHonlyH2S04only waterdilute H2SO4Ans: d343. Negative plate of an Edison cell is made ofcopperleadironsilver oxideAns: c344. The open circuit voltage of any storage cell depends wholly upon

its chemical constituentson the strength of its electrolyte(c) its temperature (d) all aboveAns: dThe specific gravity of electrolyte is measured by(a) manometer(6) a mechanical gauge(c) hydrometer(d) psychrometerAns: cWhen the specific gravity of the electrolyte of a lead-acid cell is reduced to 1.1to 1.15 the cell is in(a) charged state(b) discharged state(c) both (a) and (b)(d) active stateAns: bIn ______ system the charging current is intermittently controlled at either amaximum or minimum valuetwo rate charge controltrickle chargefloating chargean equalizing chargeAns: a348. Over chargingproduces excessive gassingloosens the active materialincreases the temperature resulting in buckling of plates(d) all above Ans: d349. Underchargingreduces specific gravity of the electrolyteincreases specific gravity of the electrolyteproduces excessive gassingincreases the temperatureAns: a350. Internal short circuits are caused bybreakdown of one or more separatorsexcess accumulation of sediment at the bottom of the cellboth (a) and (b)none of the aboveAns: c351. The effect of sulphation is that the internal resistance(a) increases (b) decreases(c) remains same (d) none of the aboveAns: a352. Excessive formation of lead sulphate on the surface of the plates happens

because ofallowing a battery to stand in discharged condition for a long timetopping up with electrolytepersistent undercharginglow level of electrolyteall aboveAns: eThe substances which combine together to store electrical energy during thecharge are called ______ materials(a) active(b) passive(c) inert(d) dielectricAns: aIn a lead-acid cell, lead is called aspositive active materialnegative active materialpassive materialnone of the aboveAns: bThe lead-acid cell should never be discharged beyond(a) 1.8 V(b) 1.9 V(c) 2 V(d) 2.1 VAns: aOn overcharging a batteryit will bring about chemical change in active materialsit will increase the capacity of the batteryit will raise the specific gravity of the electrolytenone of the above will occurAns: d357. Each cell has a vent capto allow gases out when the cell is on chargeto add water to the cell if neededto check the level of electrolyteto do all above functionsAns: dFollowing 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 aboveAns: dIn constant voltage charging method, the charging current from discharged tofully charged condition

decreasesincreasesremains constantnone of the aboveAns: a360. 48 ampere-hour capacity would deliver a current of48 amperes for 1 hour24 amperes for 2 hours8 amperes for 6 hours6 amperes for 8 hoursAns: d361. In constant-current charging method, the supply voltage from discharged tofully charged conditiondecreasesincreasesremains constantnone of the aboveAns: b362. Battery charging equipment is generally installedin well ventilated location(b) in clean and placeas near as practical to the battery being chargedin location having all above featuresAns: d363. Following will happen if the specific gravity of electrolyte becomes more than 1.23.Loss of capacityLoss of lifeCorrosion of the grids of the plateAll aboveAns: dBatteries are charged by(a) rectifiers(b) engine generator sets(c) motor generator sets(d) any one of the above methodsAns: d

Cell short circuit results in(a) low sp. gravity electrolyte(b) abnormal high temperature(c) reduced gassing on charge(d) all aboveAns: dInternal resistance of a cell is reduced by(a) using vent plug to permit gas formed during discharge

increasing the plate areaputting plates very close togetherall above methodsAns: d

Capacity of dry cells ismore when it is supplying current for intermittent periodsmore when it is supplying current for continuous periodsunaffected by the type of dischargenone of the aboveAns: aBattery container should be acid resistance, therefore it is made up

of(a) glass(b) plastic(c) wood(d) allaboveAns: dSulphated cells are indicated bythe loss of capacity of the cell(6) the decrease of the specific gravitythe low voltage of the cell on dischargeall above conditionsAns: d370. 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 ofspecific gravity of 1.36 parts of acid to 4 parts of water4 parts of acid to 4 parts of water4 parts of acid to 6 parts of water4 parts of acid to 8 parts ofwater Ans: c371. Local action in a battery is indicated byexcessive gassing under load conditionsexcessive drop in the specific gravity of electrolyte even when thecell is on open circuitboth (a) and (b)none of theabove Ans: d372. Following will happen if battery charging rate is too highexcessive gassing will occurtemperature rise will occurbulging and buckling of plates will occurall above willoccur Ans: d373. Internal resistance of a cell is due toresistance of electrolyteelectrode resistancesurface contact resistance between electrode and electrolyteall aboveAns: d

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 bevery high Ans: dIn order that a hydrometer may float vertically in electrolyte its C.G.

should beloweredraisedundisturbeddisplacedsideways Ans: a376. If a lead-acid cell is discharged below 1.8 V the following willhappen.Capacity of cell will reduceSulphation of plates will occurInternal resistance will increaseAll above willoccur Ans: d377. Life of the batteries is in the following ascending order.Lead-acid cell, Edison cell, Nickel cadmium cellLead-acid cell, Nickel-cadmium cell, Edison cellEdison cell, Nickel-cadmium cell, lead-acid cellNickel-cadmium cell, Edison cell, lead-acid cell Ans: a378. Persons preparing electrolyte should weargoggles or other face shieldrubberrubber boots and glovesall above safetydevices Ans: d379. Excessive charging a battery tends toproduce gassingincrease the internal resistance of the batteryto corrode the positive plates into lead peroxide thereby weakening

them physically(d) bring about all above changes Ans: d380. Shelf life of a small dry cell isequal to that of large dry cell(6) less than that of large dry cellmore than that of large dry cellnone of the aboveAns: b381. The current flow through electrolyte is due to the movement ofionsholeselectronsnone of theabove Ans: a

382. Level of electrolyte in a cell should be _____ the level of platesbelowequal toabovenone of theabove Ans: c383. During discharge, the active material of both the positive andnegative plates is changed toPbPb02PbOPbS04Ans: d384. of electrolytelndicates the state of charge of the batterycolourmassviscosityspecificgravity Ans: d385. The following indicate that battery on charge has attained fullchargecolour of electrodegassingspecific gravityall aboveAns: d386. Dry cell is modification ofDeniell cellLeclanche cellLead-acid cell(d) Edison cell Ans: bCapacity of a battery.is expressed in(a) Ah(b) Vh(c) Wh(d)kWhAns: aIn alkaline cell the electrolyte isdilute sulphuric acidconcentrated sulphuric acidNaOHKOHAns: d389. Self charge of a Ni-Fe cell is _____ Edison cell.equal toless thanmore thanmuch more than

Ans: bAmpere hour capacity of an industrial battery is based on ____ hours

discharge rate.(a) 8(b) 12(c) 16(d)24Ans:aThe body of Edison cell is made ofbakeliterubbernickel plated steelaluminiumAns: cSpecific gravity of electrolyte in Edison cell is(a) 0.8(b) 0.95(c) 1.1(d)1.21Ans: dAll the electrical connections between the battery and vehicle should

be by(a) thin aluminium wires(b) thin copper wires(c) rigid cables(d) flexiblecables Ans: dA battery of 6 cells will show a drop of _____ volts from fully chargedstate to fully discharged state.(a) 1.0(b) 1.5(c) 2.4(d)2.9Ans:cDuring the idle period of the battery, strong electrolyte tends tochange the active material of the cell into(a) Pb02(6) PbSC-4(c) PbO(d)PbAns:bChargmg of sulphated battery produces ____ heat.novery littleless

moreAns: d397. Hydrogen evolved during charging produces explosive mixturewhen it is more than2%4%

6%8%Ans:d398. Weston standard cell at 20°C has voltage of ____ volts.0.80.91.01871.5Ans:c399. Extent of corrosion in the underground metal work depends uponamount of moisturetype of metalstype of soil chemicalsall abovefactors Ans: d400. Mercury cell has which of the following characteristics ?(a) Flat discharge current-voltage curve(6) High power to weight ratioComparatively longer shelf life under adverse conditions of hightemperature and humidityAll of the aboveAns: d401. Charging a sulphated battery at high rate results inboiling of electrolyte due to gassingwarping of platesdamage to separators, cell caps covers and battery case due to

ex¬cessive temperatureall aboveAns: dShort 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 ofabove Ans: eIn a battery cover is placed over the element and sealed to the topof the battery container. This is doneto reduce evaporation of water from electrolyteto exclude dirt and foreign matter from the electrolyteto discharge both of the above functionsto discharge none of the abovefunctions Ans: c404. For a cell to work, which of the following condition(s) becomenecessary ?Two electrodes of different meta's should be inserted in theelectrolyte, not touching each otherElectrolyte must chemically react with one of the electrodesElectrolyte liquid or paste should be conducting

All above three conditions are necessary

Ans: dWhich of the following primary cells has the lowest

voltage ?(a) Lithium(b) Zinc-chloride(c) Mercury(d) Carbon-zinc Ans: cWhich of the following primary cells has the highest

voltage ?(a) Manganese-alkaline(6) Carbon-zinc(c) Lithium(d)MercuryAns: cWhile preparing electrolyte for a lead-acid batterywater is poured into acidacid is poured into wateranyone of the two can be added to otherchemical Ans: b408. Which of the following battery is used for air-craft?Lead-acid batteryNickel-iron batteryDry cell batterySilver oxidebattery Ans: bWhich of the following cell has a. reversible chemical

reaction ?(a) Lead-acid(b) Mercury oxide(c) Carbon-zinc(d) Silver-oxide Ans:aWhich of the following is incorrect ?A storage cell has a reversible chemical reactionA lead-acid cell can be rechargedA carbon-zinc cell has unlimited shelf lifeA primary cell has an irreversible chemicalreaction Ans: c411. Which of the following has lower sp. gravity VDilute H2S04Concentrated H2SO4WaterAny of the aboveAns: c412. Under normal charging rate, the charging currentshould be10% of capacity

20% of capacity30% of capacity40% of capacityAns: a

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 internalresistance Ans: aA typical output of a solar cell is0.1V0.26 V1.1 V2 VAns:b415. Petroleum jelly is applied to the electrical connections to the lead-acid batteryprevent local heatingprevent short-circuitingreduce path resistancepreventcorrosion Ans: d416. When the load resistance equals the generator resistance which ofthe following will be maximum ?CurrentEfficiency of the circuitPower in the load resistanceVoltage across the loadresistance Ans: c417. The common impurity in the electrolyte of lead-acid battery ischlorinedust particleslead crystalsironAns:d418. In a lead-acid battery the energy is stored in the form of(a) charged ions(b) chemical energy(c) electrostatic energy(d) electromagnetic energyAns: b419. Which among the following constitutes the major load for an ?(a)Self starterParking lightsSpark plugsAns: b420. Which of the following factors adversely affects the capacity of theleadacid battery ?Temperature of surroundingsSpecific gravity of electrolyteRate of discharge

All of the above

Ans: dCells are connected in parallel to(a) increase the efficiency(b) increase the current capacity(c) increase the voltage output(d) increase the internalresistance Ans: bA constant-voltage generator has(a) minimum efficiency(b) minimum current capacity(c) low internal resistance(d) high internal resistanceAns: c423. The property of coil by which a counter e.m.f. is induced in itwhen the current through the coil changes is known asself-inductancemutual inductanceseries aiding inductancecapacitance

Ans: aAs 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 themagnetic field Ans: cWhich of the following circuit element stores energy in the electromagnetic field ?InductanceCondenserVariable resistorResistanceAns: aThe 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 ofthe core Ans: aHigher the self-inductance of a coil,lesser its weber-turnslower the e.m.f. inducedgreater the flux produced by it

longer the delay in establishing steady currentthrough it Ans: d

428. In an iron cored coil the iron core is removed so that the coil becomesan air cored coil. The inductance of the coil will

increasedecreaseremain the same

initially increase and thendecrease Ans: b429. An open coil haszero resistance and inductanceinfinite resistance and zero inductanceinfinite resistance and normal inductance

zero resistance and highinductance Ans: b

430. Both the number of turns and the core length of an inductivecoil are doubled. Its self-inductance will beunaffecteddoubledhalved

quadrupledAns: b431. If current in a conductor increases then according to Lenz's law self-induced voltage willaid the increasing currenttend to decrease the amount of cur-rentproduce current opposite to the in-creasing current

aid the appliedvoltage Ans: c432. The direction of incViced e.m.f. can be found byLaplace's lawLenz's lawFleming's right hand rule

Kirchhoff s voltagelaw Ans: b433. Air-core coils are practically free fromhysteresis losseseddy current lossesboth (a) and (b)

none of theabove Ans: c434. The magnitude of the induced e.m.f. in a conductor depends on theflux density of the magnetic fieldamount of flux cutamount of flux linkages

rate of change of flux-linkages Ans: d

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 theabove Ans: dA laminated iron core has reduced eddy-current losses becausemore wire can be used with less D.C. resistance in coilthe laminations are insulated from each otherthe magnetic flux is concentrated in the air gap of the corethe laminations are stacked vertf-callyAns: bThe 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)CoulombAns: bWhich of the following is not a unit of inductance ?HenryCoulomb/volt ampereVolt second per ampereAll of the aboveAns: bIn 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: bWhich of the following circuit elements will oppose the change in circuit

current ?(a) Capacitance(b) Inductance(c) Resistance

(d) All of theabove Ans: bFor a purely inductive circuit which of the following is true ?Apparent power is zeroRelative power is.zeroActual power of the circuit is zero

Any capacitance even if present in the circuit will notbe charged Ans: c

Which of the following is unit of inductance ?(a) Ohm(b) Henry(c) Ampere turns

(d)Webers/metreAns: bAn 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) 4A/sAns: d

The core of a coil has a length of 200 mm. The inductance of coil is 6 mH. Ifthe core length is doubled, all other quantities, remaining the same, the inductance will be(a) 3 mH(b) 12 mH

(c)24mH(d)48mH Ans:a

The self inductances of two coils are 8 mH and 18 mH. If the co-efficients ofcoupling is 0.5, the mutual inductance of the coils is(a) 4 mH(b) 5 mH(c) 6 mH

(d) 12mHAns: c

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) 48mHAns: b

A 200 turn coil has an inductance of 12 mH. If the number of turns is increasedto 400 turns, all other quantities (area, length etc.) remaining the same, theinductance will be(a) 6 mH

(b) 14 mH(c) 24 mH

(d) 48mHAns: d

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

6 H8 H12 H

24 HAns: c449. In case all the flux from the current in coil 1 links with coil 2, the co-efficient ofcoupling will be2.01.00.5

zeroAns: b450. A coil with negligible resistance has 50V across it with 10 mA. The inductivereactance is50 ohms500 ohms1000 ohms

5000 ohmsAns: d

451. A conductor 2 metres long moves at right angles to a magnetic field of fluxdensity 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the conductorwill be10 V(6) 15 V25V

50VAns: c452. Lenz's law is a consequence of the law of conservation ofinduced currentchargeenergy

induced e.m.f.Ans: c

453. A conductor carries 125 amperes of current under 60° to a magnetic field of1.1 tesla. The force on the conductor will benearly50 N120 N240 N

480 NAns: 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

400 N600 N

1000 NAns: a455. The co-efficient of coupling between two air core coils depends onself-inductance of two coils onlymutual inductance between two coils onlymutual inductance and self inductance of two coils

none of theabove Ans: c

456. An average voltage of 10 V is induced in a 250 turns solenoid as a result of achange in flux which occurs in 0.5 second. The total flux change is20 Wb2 Wb0.2 Wb

0.02 WbAns: d

457. A 500 turns solenoid develops an average induced voltage of 60 V. Over whattime interval must a flux change of 0.06 Wb occur to produce such a voltage ?0.01 s0.1 s0.5 s

5 sAns:c458. Which of the fpllowing inductor will have the least eddy current losses ?Air coreLaminated iron coreIron core

Powdered ironcore Ans: a459. A coil induces 350 mV when the current changes at the rate of 1 A/s. Thevalue of inductance is3500 mH350 mH250 mH

150 mHAns: b460. Two 300 uH coils in series without mutual coupling have a total inductance of300 uH600 uH150 uH

75 uHAns: b

Current changing from 8 A to 12 A in one second induced 20volts in a coil. The value of inductance is(a) 5 mH(b) 10 mH(c) 5 H

(d) 10H Ans:cWhich circuit element(s) will oppose the change in circuit current ?Resistance onlyInductance onlyCapacitance only

Inductance andcapacitance Ans: b463. A crack in the magnetic path of an inductor will result inunchanged inductanceincreased inductancezero inductance

reducedinductance Ans: d

464. A coil is wound on iron core which carries current I. The self-inducedvoltage in the coil is not affected byvariation in coil currentvariation in voltage to the coilchange of number of turns of coil

the resistance of magneticpath Ans: b465. A moving magnetic field will produce the same effect as a conductor thatis moving.Yes

NoAns:466. The polarity of the induced voltage can be determined by using the left-hand generator rule.Yes

NoAns:a467. Increasing the field or increasing the current will decrease the force onthe conductor.Yes

NoAns:b468. Reversing the field or the current will reverse the force on the conductor.

Yes

NoAns:a

469 When a conductor moves in the field, so that it makes an angle 8 with the linesof flux, the force F is given as : F = Bl sin2 0.Yes

NoAns: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 unitweber turns.Yes

NoAns:b471. Laminations of core are generally made ofcase ironcarbonsilicon steel

stainlesssteel Ans: c472. Which of the following could be lamina-proximately the thickness of lamina-tions of a D.C. machine?0.005 mm0.05 mm0.5 m

5 mAns:c473. The armature of D.C. generator is laminated toreduce the bulkprovide the bulkinsulate the core

reduce eddy currentloss Ans: d474. The resistance of armature winding depends onlength of conductorcross-sectional area of the conductornumber of conductorsall of the aboveAns: d475. The field coils of D.C. generator are usually made ofmicacoppercast iron

carbonAns: b

The commutator segments are connected to the armature conductors by meansof

(a) copper lugs(b) resistance wires

(c) insulationpads Ans: aIn a commutatorcopper is harder than micamica and copper are equally hardmica is harder than coppernone of the aboveAns: cIn D.C. generators the pole shoes are fastened to the pole core by(a) rivets(b) counter sunk screws(c) brazing

(d)weldingAns: b

According to Fleming's right-hand rule for finding the direction of inducede.m.f., when middle finger points in the direction of induced e.m.f., forefingerwill point in the direction of(a) motion of conductor(b) lines of force(c) either of the above

(d) none of theabove Ans: bFleming's right-hand rule regarding direction of induced e.m.f., correlatesmagnetic flux, direction of current flow and resultant forcemagnetic flux, direction of motion and the direction of e.m.f. inducedmagnetic field strength, induced voltage and current

magnetic flux, direction of force and direction of motion ofconductor Ans: b

481. While applying Fleming's right-hand rule to And the direction of inducede.m.f., the thumb points towardsdirection of induced e.m.f.direction of fluxdirection of motion of the conductor if forefinger points in the direction of

generated e.m.f.

direction of motion of conductor, if forefinger points along thelines of flux Ans: d482. The bearings used to support the rotor shafts are generallyball bearingsbush bearings

magnetic bearmgsneedle bearing

Ans: a483. In D.C. generators, the cause of rapid brush wear may besevere sparkingrough commutator surfaceimperfect contact

any of theabove Ans: d484. In lap winding, the number of brushes is alwaysdouble the number of polessame as the number of poleshalf the number of poles

twoAns:b

485. For a D.C. generator when the number of poles and the number of armatureconductors is fixed, then which winding will give the higher e.m.f. ?Lap windingWave windingEither of (a) and (b) above

Depends on other features ofdesign Ans: b486. In a four-pole D.C. machineall the four poles are north polesalternate poles are north and southall the four poles are south polestwo north poles follow two south polesAns: b487. Copper brushes in D.C. machine are usedwhere low voltage and high currents are involvedwhere high voltage and small cur-rents are involvedin both of the above casesin none of the above casesAns: a488. A separately excited generator as compared to a self-excited generatoris amenable to better voltage con-trolis more stablehas exciting current independent of load currenthas all above features

Ans: d489. In case of D.C. machines, mechanical losses are primary function ofcurrentvoltage

speednone of aboveAns: cIron losses in a D.C. machine are independent of variations in(a) speed(b) load(c) voltage(d) speed and voltageAns: bIn D.C. generators, current to the external circuit from armature is given

throughcommutatorsolid connectionslip rings

none of aboveAns: a492. Brushes of D.C. machines are made ofcarbonsoft copperhard copper

all of aboveAns: a

493. If B is the flux density, I the length of conductor and v the velocity ofconductor, then induced e.m.f. is given by(a)Blv(b)Blv2(c)Bl2v

(d)Bl2v2Ans: a

494. In case of a 4-pole D.C. generator provided with a two layer lap winding withsixteen coils, the pole pitch will be4816

32Ans:b495. The material for commutator brushes is generallymicacoppercast iron

carbonAns: d

496. The insulating material used between the commutator segments is normally

graphitepapermicainsulating varnishAns: c497. In D.C. generators, the brushes on commutator remain in contact with conductors whichlie under south polelie under north polelie under interpolar region

are farthest from thepoles Ans: c

498. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will bedemagnetisation onlycross magnetisation as well as magnetisationcrossmagnetisation as well as demagnetisingcross magnetisation onlyAns: cArmature reaction of an unsaturated D.C. machine is(a) crossmagnetising(b) demagnetising(c) magnetising

(d) none ofabove Ans: a

D.C. generators are connected to the busbars or disconnected from them onlyunder 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) allaboveAns: dEddy currents are induced in the pole shoes of a D.C. machine due tooscillating magnetic fieldpulsating magnetic fluxrelative rotation between field and armatureall aboveAns: c502. In a D.C. machine, short-circuited field coil will result inodour of barning insulationunbalanced magnetic pull producing vibrationsreduction of generated voltage for which excitation has to be increased to

maintain the voltage

all above

Ans: d503. Equilizer rings are required in case armature iswave woundlap wounddelta wound

duplex woundAns: b504. Welding generator will havelap windingwave windingdelta winding

duplex wavewinding Ans: a505. In case of D.C. machine winding, number of commutatorsegments is equal tonumber of armature coilsnumber of armature coil sidesnumber of armature conductors

number of armatureturns Ans: a506. For a D.C. machines laboratory following type of D.C. supplywill be suitablerotary convertermercury are rectifierinduction motor D.C. generator set

synchronous motor D.C.generator set Ans: c507. The function of pole shoes in the case of D.C. machine isto reduce the reluctance of the magnetic pathto spread out the flux to achieve uniform flux densityto support the field coil

to discharge all the abovefunctions Ans: d508. In the case of lap winding resultant pitch ismultiplication of front and back pitchesdivision of front pitch by back pitchsum of front and back pitches

difference of front and backpitches Ans: d509. A D.C. welding generator haslap windingwave movingduplex windingany of the above

Ans: a510. Which of the following statement about D.C. generators is false ?Compensating winding in a D.C. machine helps in commutationIn a D. C. generator interpoles winding is connected in series with the armature

windingBack pitch and front pitch are both odd and approximately equal to the pole pitchEquilizing bus bars are used with parallel running of D.C. shunt generatorsAns: dThe 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 sparkingtrouble Ans: aMagnetic field in a D.C. generator is produced byelectromagnetspermanent magnetsboth (a) and (b)

none of theabove Ans: a513. The number of brushes in a commutator depends onspeed of armaturetype of windingvoltage

amount of current to becollected Ans: d514. Compensating windings are used in D.C. generatorsmainly to reduce the eddy currents by providing local short-circuitsto provide path for the circulation of cooling airto neutralise the cross-magnetising effect of the armature reactionnone of the aboveAns: c

Which of the following components of a D.C, generator plays vital role forproviding direct current of a D.C. generator ?(a) Dummy coils(b) Commutator(c) Eye bolt

(d) Equilizerrings Ans: bIn a D.C. generator the ripples in the direct e.m.f. generated are reduced byusing conductor of annealed copperusing commutator with large number of

segmentsusing carbon brushes of superior quality

(d) using equiliser rings Ans: cIn 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, lowcurrent Ans: b

Two generators A and B have 6-poles each. Generator A has wave wound armaturewhile generator B has lap wound armature. The ratio of the induced e.m.f. isgenerator A and B will be(a) 2 : 3(b) 3 : 1(c) 3 : 2

(d) 1 :3 Ans:bThe voltage drop for which of the following types of brush can be expected to be

least ?Graphite brushesCarbon brushesMetal graphite brushesNone of the aboveAns: c

520. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole fluxremains , if the speed of the generator is doubled, the e.m.f. generated will beE/22Eslightly less than EEAns: bIn a D.C. generator the actual flux distribution depends upon(a) size of air gap(b) shape of the pole shoe(c) clearance between tips of the ad¬jacent pole shoes

(d) all of theabove Ans:The armature core of a D.C. generator is usually made ofsilicon steelcoppernon-ferrous materialcast-ironAns: a523. Satisfactory commutation of D.C. machines requires

(a) brushes should be of proper grade and size

brushes should smoothly run in the holderssmooth, concentric commutator properly undercutall of the aboveAns: d524. Open circuited armature coil of a D.C. machine isidentified by the scarring of the commutator segment to which open circuited

coil is connectedindicated by a spark completely around the commutatorboth (a) and (b)none of the aboveAns: c525. In a D.C. machine, fractional pitch winding is usedto increasethe generated voltageto reduce sparkingto save the copper because of shorter end connections

due to (b) and (c)above Ans:526. For the parallel operation of two or more D.C. compound generators, weshould ensure thatvoltage of the incoming generator should be same as that of bus barpolarity of incoming generator should be same as that of bus barall the series fields should be run in parallel by means of equilizer connectionseries fields of all generators should be either on positive side or negative side

of the armatureall conditions mentioned above should be satisfiedAns: d527. D.C. series generator is usedto supply traction loadto supply industrial load at constant voltagevoltage at the toad end of the feederfor none of the above purposeAns: c

528. Following D.C. generator will be in a position to build up without any magnetism in the poles

series generatorshunt generatorcompound generator

self-excitedgenerator Ans: d529. Interpole flux should be sufficient toneutralise the commutating self induced e.m.f.neutralise the armature reaction flux

neutralise both the armature reaction flux as well as commutating e.m.f.induced in the coil

perform none of the abovefunctions Ans: c

530. D.C. generator generally preferred for charging automobile batteries isseries generatorshunt generatorlong shunt compound generatorany of'the aboveAns: cIn 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 ofpoles is 2 Ans: dPermeance is the reciprocal offlux densityreluctanceampere-turns

resistanceAns: b533. In D.C. generators the polarity of the interpolesis the same as that of the main pole aheadis the same as that of the immediately preceding poleis opposite to that of the main pole ahead

is neutral as these poles do not play part ingenerating e.m.f. Ans: a534. The e.m.f. generated in a D.C. generator is directly proportional toflux/polespeed of armaturenumber of poles

all of theabove Ans: b535. In a D.C. generator the magnetic neutral axis coincides with the geometricalneutral axis, whenthere is no load on|he generatorthe generator runs on full loadthe generator runs on overload

the generator runs on designedspeed 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 exceptinterpolesdummy coilscompensating windingshifting of axis of brushes

Ans: bIn D.C. generators on no-load, the air gap flux distribution in space is(a) sinusoidal(b) triangular(c) pulsating

(d) flattoppedAns: d

A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If thespeed increases to 1200 r.p.m., the generated e.m.f. will be nearly(a) 150 V(b) 175 V(c) 240 V

(d) 290V Ans:cThe purpose of providing dummy coils in a generator isto reduce eddy current lossesto enhance flux densityto amplify voltage

to provide mechanical balance for therotor Ans: d540. In a shunt generator the voltage build up is generally restricted byspeed limitationarmature heatinginsulation restrictions

saturation ofiron Ans:541. If a D.C. generator fails to build up the probable cause could not beimperfect brush contactfield resistance less than the critical resistanceno residual magnetism in the generator

faulty shunt connections tending to reduce the residualmagnetism Ans: b542. Flashing the field of D.C. generator meansneutralising residual magnetismcreating residual magnetism by a D.C. sourcemaking the magnetic losses of forces parallel

increasing flux density by adding extra turns ofwindings on poles Ans: b

543. The e.m.f. induced in the armature of a shunt generator is 600 V. Thearmature resistance is 0.1 ohm. If the armature current is 200 A, the terminalvoltage will be640 V

600 V

580 VAns: d544. In a D.C. generator the critical resistance refers to the resistance ofbrushesfieldarmature

loadAns: b

545. To achieve sparkless commutation brushes of a D.C. generator are rockedmahead so as to bring themjust ahead of magnetic neutral axisin magnetic neutral axis

just behind the magneticneutral axis Ans: a546. Armature coil is short circuited by brushes when it liesalong neutral axisalong field axisin any of the above positions

in none of the abovepositions Ans: a547. A cumulatively compounded long shunt generator when operating as amotor would becumulatively compounded long shuntdifferentially compounded long shuntcumulatively compounded short shunt

differentially compounded shortshunt Ans: b548. To avoid formation of grooves in the commutator of a D.C. machinethe brushes of opposite polarity should track each otherthe brushes of same polarity should track each other

brush position has no effect on the commutatorgrooving Ans: a549. The following constitute short-circuit in the armature winding.Insulation failure between two com-mutator bars(6) Insulation failure between two turns of a coilTwo of more turns of the same coil getting grounded

All of theabove Ans: d550. The rapid wear of brushes takes place due toabrasion from dustexcessive spring pressurerough commutator bars

high mica insulation between com-mutation barsall of the above factorsAns: eNumber 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 commutatorsegments Ans: aA D.C. generator can be considered asrectifierprimemoverrotating amplifier

power pumpAns: c

553. In any rotating machine that part which houses the conductors and in whiche.m.f. induced is to be utilised is calledrotorstatorfield

armatureAns: d554. In a D.C. machine stray loss is the sum oftotal copper loss and mechanical lossarmature copper loss and iron lossshunt field copper loss and mechanical loss

iron loss and mechanicalloss Ans: d555. Lap winding is composed ofany even number of conductorsany odd number of conductorsthat even number which is exact multiple of poles + 2

that even number which is exact multipleof poles Ans: a556. In a D.C. generator in case the resistance of the field winding is increased,then output voltage willincreasedecreaseremain unaffected

fluctuateheavily Ans: b557. An exciter for a turbo generator is aseparately excited generator

shunt generatorseries generator

compoundgenerator Ans: b558. In case of a flat compounded generatorvoltage generated is less than the rated voltagegenerated voltage is proportional to the load on the generatorvoltage remains constant irrespec¬tive of the load

speed varies in proportion to the load on thegenerator Ans: c559. Which of the following generator will have negligible terminal voltage whilerunning on no-load ?Series generatorShunt generatorCompound generator

Separately excitedgenerator Ans: a

560. Which of the following D.C. generators will be in a position to build upwithout any residual magnetism in the poles ?Series generatorShunt generatorCompound generator

None of theabove Ans: d561. In over compounded generator, full load terminal voltage isalmost zeroless than noload terminal voltagemore than noload terminal voltage

equal to no-load terminalvoltage Ans: c562. In a level compounded D.C. generator, full load terminal voltage isnegligibly lowequal to no-load terminal voltagemore than no-load terminal voltage

less than no-load terminalvoltage Ans: b

563. The terminal voltage of a D.C. shunt generator drops on load because of all ofthe following reasons exceptarmature reactionarmature resistance dropfield weakening due to armature reaction and armature

commutationAns: d

564. In a D.C. generatorexternal resistance = internal char-acteristic - armature reactioninternal characteristic = magnetisation characteristic - ohmic dropexternal characteristic = magnetisation characteristic - ohmic drop - armature

reactionmagnetisation characteristic = external characteristicAns: cA 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 vHz 5 Ans: bA 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) 220V Ans:bIn a separately excited generator supplying rated load the armature reaction ,is always presentis always absentmay be sometimes presentnone of the aboveAns: aIf 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)highAns: aArmature reaction in a generator results indemagnetisation of leading pole tip and magnetisation of trailing pole tipdemagnetisation of trailing pole tip and magnetisation of leading pole tipdamagnetising the centre of all poles

magnetising the centre of allpoles Ans: a

570. Following energized winding of a D.C. machine should not be opened as itwould produce high inductive voltage which may be dangerous to personneland may cause its own insulation failure.

Series fieldCompensating fieldInter pole fieldShunt field

Ans: dWave 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 exactmultiple of poles Ans: cThe critical resistance of the D.C. generator is the resistance of(a) field(b) brushes(c) armature

(d)loadAns: aWhen 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 theload

(d) to reduce the combined effect of ar-mature reaction ofboth machines Ans: cWhich 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 theabove Ans: cWhich 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 theabove Ans: a

Two generators are running in parallel. One of the generators may run as motorfor 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 largeshare of loads Ans: dA D.C. generator works on the principle ofLenz's law

Ohm's lawFaraday's law of electromagnetic induction

(d) none of the above Ans: cA 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 theabove Ans: bA 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

irrespective of the value of the resis-tance in thefield circuit Ans: a

580. The terminal voltage of a series generator is 150 V when the load current is 5A. If the load current is increased to 10 A, the terminal voltage will be150 Vless than 150 Vgreater than 150 Vnone of the aboveAns: cThe 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 theabove Ans: c

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 VAns: bThe essential condition for parallel operation of two D.C. generators is that they

have 'same kW ratingthe same operation r.p.m.the same drooping voltage charac-teristicssame percentage regulationAns: c584. When two D.C. generators are running in parallel an equilizer bar is used

(a) to increase the series flux

to increase the generated e.m.f.to reduce the combined effect of ar-mature reaction of both the machines

so that the two identical machines will pass approximately equalcurrents to the load Ans: d585. With a D.C. generator which of the following regulation is preferred ?100% regulationinfinite regulation50% regulation

1% regulationAns: d586. Which generator would you prefer for feeding long D.C. transmission lines ?Series generatorShunt generatorOver compound generator

Flat compoundgenerator Ans: c587. In a D.C. generator the critical resistance can be increased byincreasing its field resistancedecreasing its field resistanceincreasing its speed

decreasing itsspeed Ans: c588. The number of armature parallel paths in a two-pole D.C. generator havingduplex lap winding is246

8 Ans: b589. For both lap and wave windings, there are as many commutator bars as thenumber ofslotsarmature conductorswinding elements

polesAns: c590. The series field of a short-shunt D.C. generator is excited byexternal currentarmature currentshunt current

load currentAns: d

591. As a result of armature reaction, the reduction in the total mutual air gap fluxin a D.C. generator is approximately

40 percent25 percent10 percent

5 percentAns: d592. Shunt generators are most suited for stable parallel operation because of theirrising voltage characteristicsidentical voltage characteristicsdrooping voltage characteristics

linear voltagecharacteristics Ans: c

593. The main factor which leads to unstable parallel operation of flat and overcompounded generators istheir rising voltage characteristicsunequal number of turns in their series field windingsunequal speed regulation of their primemovers

unequal series fieldresistances Ans: a

594. If a self excited D.C. generator after being installed, fails to build up on itsfirst trial run, the first is to

reverse the field connectionsincrease the field resistanceincrease the speed of primemover(d) check armature insulation resis¬tanceAns: a595.No-load speed of which of the following motor will be highest ?Shunt motorSeries motorCumulative compound motorDifferentiate compound motorAns: b596. The direction of rotation of a D.C. series motor can be changed byinterchanging supply terminalsinterchanging field terminalseither of (a) and (b) aboveNone of the aboveAns: b597. Which of the following application requires high starting torque ?Lathe machineCentrifugal pumpLocomotiveblowerAns: c

598. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?Series motorShunt motorDifferentially compound motor

Cumulative compoundmotor Ans: a599. Which D.C. motor will be preferred for machine tools ?Series motorShunt motorCumulative compound motorDifferential compound motorAns: b600. Differentially compound D.C. motors can find applications requiringhigh starting torquelow starting torquevariable speedfrequent on-off cyclesAns: b601. Which D.C. motor is preferred for elevators ?Shunt motorSeries motorDifferential compound motorCumulative compound motorAns: 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 ofcurrent in the conductor aovtaat of conductorresultant force on conductornone of the aboveAns: aIf 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 nuvatconstant speed Ans: cStarters are used with D.C. motors becausethese motors have high starting torquethese 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 reducedthe speed will increase abruptlythe speed will increase in proportion to reduction in loadthe speed will remain almost/constantthe speed will reduceAns: c606. A D.C. series motor is that whichhas its field winding consisting of thick wire and less turnshas a poor torquecan be started easily without loadhas almost constant speedAns: a607. For starting a D.C. motor a starter is required because(a) it the speed of the motorit limits the starting current to a safe valueit starts the motornone of the aboveAns: b608. The type of D.C. motor used for shears and punches isshunt motorseries motordifferential compoutid D.C. motorcumulative compound D.C. motorAns: d609. If a D.C. motor is connected across the A.C. supply it willrun at normal speednot runrun at lower speedburn due to heat produced in the field winding by .eddy currentsAns: d610.To get the speed of D.C, motor below the normal without wastage of electrical energy is used.Ward Leonard controlrheostatic controlany of the above method

none of the abovemethod Ans: a611. When two D.C. series motors are connected in parallel, the resultant speed ismore than the normal speedloss than the normal speednormal speedzeroAns: c

612. The speed of a D.C. shunt motor more than its full-load speed can be obtained bydecreasing the field currentincreasing the field currentdecreasing the armature current

increasing the armaturecurrent Ans: a613. In a D.C. shunt motor, speed isindependent of armature currentdirectly proportional to the armature currentproportional to the square of the currentinversely proportional to the armature currentAns: a614. A direct on line starter is used: for starting motorsiip to 5 H.P.up to 10 H.P.up to 15 H.P.up to 20 H.P.Ans: a615. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?The motor will stopThe motor will continue to runThe armature may burnThe motor will run noisyAns: c616. In case of D.C. shunt motors the speed is dependent on back e.m.f. only becauseback e.m.f. is equal to armature droparmature drop is negligibleflux is proportional to armature currentflux is practically constant in D:C. shunt motorsAns: d

617. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will bealmost negligiblerated full-load currentless than full-load currentmore than full-load currentAns: d618. These days D.C. motors are widely used inpumping setsair compressorselectric tractionmachine 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?FrameShaftCommutatorStatorAns: c

620. In which of the following applications D.C. series motor is invariably tried?Starter for a carDrive for a water pumpFan motor(d) Motor in A.C. or D.C.Ans: a621.

In D.C. machines fractional pitch winding is used

to improve coolingto reduce copper lossesto increase the generated e.m.f.to reduce the sparkingAns: dA 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

In case-the conditions for maximum power for a D.C. motor are established, theefficiency of the motor will be100%around 90%anywhere between 75% and 90%less than 50%Ans: d624. The ratio of starting torque to full-load torque is least in case ofseries motorsshunt motorscompound motorsnone of the aboveAns: b625. In D.C. motor which of the following can sustain the maximum temperature rise?(a) Slip rings

CommutatorField winding

Armature windingAns: c626. 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-handrule Ans: d627. Which of the following load normally needs starting torque more than the rated torque?BlowersConveyorsAir compressorsCentrifugal pumpsAns: b628. The starting resistance of a D.C. motor is generallylowaround 500 Q1000 Qinfinitely largeAns: a629. The speed of a D.C. series motor isproportional to the armature currentproportional to the square of the armature currentproportional to field current

inversely proportional to the armaturecurrent Ans: d

630. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equalto100% of the previous value50% of the previous value25% of the previous value10% of the previous valuenone of the aboveAns: c631. The current drawn by the armature of D.C. motor is directly proportional tothe torque requiredthe speed of the motorthe voltage across the terminals

(d) none of the above Ans: a632. The power mentioned on the name plate of an electric motor indicatesthe power drawn in kWthe power drawn in kVAthe gross powerthe output power available at the shaftAns: d633. Which D.C. motor has got maximum self loading property?Series motorShunt motorCumulatively compounded 'motor

Differentially compoundedmotor Ans: d634. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?Series motorShunt motorCumulatively compounded motor

Differentially compoundedmotor Ans: cIf 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 excessivecentrifugal stresses

(d) motor will run at veryslow speed Ans: cD.C. series motors are usedwhere load is constantwhere load changes frequentlywhere constant operating speed is neededin none of the above situations.Ans: dFor 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: cIn case of conductively compensated D.C. series motors, the compensating winding

is provided

as separately wound unitin parallel with armature

winding(c) in series with armature winding

(d) in parallel with field winding Ans: c639. Sparking at the commutator of a D.C. motor may result indamage to commutator segmentsdamage to commutator insulationincreased power consumptionall of the aboveAns: d640. Which of the following motor is preferred for operation in highly explosive atmosphere ?Series motorShunt motorAir motor

Battery operatedmotor Ans: c641. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?Starting torqueOperating speedFull-load current

All of the aboveAns: c642. Which one of the following is not the function of pole shoes in a D.C. machine ?To reduce eddy current lossTo support the field coilsTo spread out flux for better unifor-mity

To reduce the reluctance of the mag-neticpath Ans: a

The mechanical power developed by a shunt motor will be maximum when theratio of back e.m.f. to applied voltage is(a) 4.0(b) 2.0(c) 1.0

(d)0.5Ans:dThe condition for maximum power in case of D.C. motor isback e.m.f. = 2 x supply voltageback e.m.f. = | x supply voltagesupply voltage = | x back e.m.f.

supply voltage = backe.m.f. Ans: b

645. For which of the following applications a D.C. motor is preferred over an A.C. motor ?Low speed operationHigh speed operation

Variable speed operation

Fixed speed operationAns: cIn 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 percent Ans: aWhich D.C. motor is generally preferred for cranes and hoists ?(a) Series motor(b) Shunt motor(c) Cumulatively compounded motor

(d) Differentiallycompounded motor Ans: aThree point starter can be used forseries motor onlyshunt motor onlycompound motor onlyboth shunt and compound motorAns: d649. Sparking, is discouraged in a D.C. motor becauseit increases the input power con-sumptioncommutator gets damagedboth (a) and (b)none of the aboveAns: b650. Speed control by Ward Leonard method gives uniform speed variationin one directionin both directionsbelow normal speed only

above normal speedonly. Ans: b

651. Flywheel is used with D.C. compound motor to reduce the peak demand by themotor, compound motor will haveto belevel compoundedunder compoundedcumulatively compounded

differentiallycompounded Ans: c652. Following motor is used where high starting torque and wide speed range control is required.

Single phase capacitor startInduction motorSynchronous motorD.C. motorNone of the aboveAns: d653. In a differentially compounded D.C. motor, if shunt field suddenly opensthe motor will first stop and then run in opposite direction as series motorthe motor will work as series motor and run at slow speed in the same directionthe motor will work as series motor and run at high speed in the same directionthe motor will not work and come to stopAns: a654. Which of the following motor has the poorest speed regulation ?Shunt motorSeries motorDifferential compound motorCumulative compound motorAns: b655. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use ofD.C. series motorD.C. shunt motorinduction motorall of above motorsAns: a656. As -the load is increased the speed of D.C. shunt motor willreduce slightlyincrease slightlyincrease proportionatelyremains unchangedAns: a657. The armature torque of the D.C. shunt motor is proportional tofield flux onlyarmature current onlyboth (a) and (b)

none of the aboveAns: b658. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?Voltage control methodField control methodArmature control methodAll above methodsAns: c

659. Usually wide and sensitive speed control is desired in case ofcentrifugal pumpselevatorssteel rolling mills

colliery windersAns: d

The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at ratedload. The speed regulation of the motor is(a) 2.36%(6) 4.76%(c) 6.77%

(d)8.84%Ans: bThe armature voltage control of D.C. motor providesconstant torque driveconstant voltage driveconstant current drive

none of the aboveAns: 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 circuita resistance is connected in series with armaturea resistance is connected parallel to the armaturearmature is temporarily open circuited

a high value resistor is connected across the fieldwinding Ans: a663. The speed of a D.C. shunt motor can be increased byincreasing the resistance in armature circuitincreasing the resistance in field circuitreducing the resistance in the field circuitreducing the resistance in the armature circuitAns: b664. If I2 be the armature current, then speed of a D.C. shunt motor isindependent of Iaproportional to lavaries as (Ia)varies as laAns: 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 willremain unchangedreduce to one-fourth value

increase four foldsbe doubledAns: a666. At the instant of starting when a D.C. motor is put on supply, it behaves likea highly resistive circuita low resistance circuita capacitive circuit

none of the aboveAns: b667. The speed of a D.C. motor can be varied by varyingfield currentapplied voltageresistance in series with armatureany of the aboveAns: d668. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?Low costWide speed rangeStabilityHigh starting torque.Ans: a669. For a D.C. shunt motor if the excitation is changedtorque will remain constanttorque will change but power will remain constanttorque and power both will changetorque, power and speed, all will changeAns: bWhich motor has the poorest speed control?(a) Differentially compounded motor(b) Cumulatively compounded motor(c) Shunt motor

(d) Seriesmotor Ans: dThe plugging gives thezero torque brakingsmallest torque brakinghighest torque brakingnone of the aboveAns: c672. The armature voltage control of D.C. motor providesconstant voltage driveconstant current drive

constant torque drive

none of the aboveAns: c

673. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motorof lower H.P. should be selectedof higher H.P. should be selectedcan be used for 50°C ambient temperature also

is to be derated by a factor recom-mended by manufacturer and select the nexthigher H.P. motor Ans: d

674. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of brakingregenerativepluggingdynamic brakingnone of the aboveany of the aboveAns: b675. Which of the following motors one will choose to drive the rotary compressor ?D.C. shunt motorD.C. series motorUniversal motor

Synchronous motorAns: dIf 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) becomezero Ans: aWhy are the D.C. motors preferred for traction applications ?Torque and speed are inversely proportional to armature currentTorque is proportional to armature currentTorque is proportional to square root of armature current

The speed is inversely proportional to the torque and the torque isproportional to square of armature currentAns: d678. Which of the following motors is usually used in house-hold refrigerators ?D.C. shunt motorD.C. series motorSingle phase induction motor (split phase start or induction run motor)Reluctance motor

(e) Synchronous motorAns: c679. Which of the following motors is most suitable for signallingand many kinds of timers ?D.C. shunt motorD.C. series motorInduction motorReluctance motorAns: dWhich motor should not be started on no-load ?(a) Series motor(b) Shunt motor(c) Cumulatively compounded motor

(d) Differentially compoundedmotor. Ans: aWard-Leonard control is basically avoltage control methodfield divertor methodfield control method

armature resistance controlmethod Ans: aFor constant torque drive which speed control method is preferred ?(a) Field control(b) Armature voltage control(c) Shunt armature control

(d) Mechanical loadingsystem Ans: bIn Ward-Leonard control the lower limit of speed is imposed byresidual magnetism of the generatorcore losses of motormechanical losses of motor and gen¬erator togetherall of the aboveAns: a684. The main disadvantage of the Ward-Leonard control method ishigh initial costhigh maintenance costlow efficiency at Hght loadsall of the aboveAns: d685. Regenerative method of braking is based on thatback e.m.f. is less than the applied voltageback e.m.f. is equal to the applied voltageback e.m.f. of rotor is more than the applied voltage

(d) none of the above Ans: b686. The hysteresis loss in a D.C. machine least depends onFrequency of magnetic reversalsMaximum value of flux densityVolume and grade of ironRate of flow of ventilating airAns: d687. In a D.C. generator all of the following could be the effects of iron losses exceptLoss of efficiencyExcessive heating of coreIncrease in terminal voltage

Rise in temperature of ventilatingair 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 ?hysteresis lossfield copper lossarmature copper losseddy current lossAns: c689. Which of the following loss in a D.C. generator varies significantly with the load current ?Field copper lossWindage lossArmature copper lossNone of the aboveAns: c690. Torque developed by a D.C. motor depends uponmagnetic fieldactive length of the conductorcurrent flow through the conductorsnumber of conductorsradius of armatureall above factorsAns: fD.C. shunt motors are used for driving(a) trains(b) cranes(c) hoists

(d) machinetools Ans: dIn a manual shunt motor starter

(a) over load is connected in series and no volt relay in parallel with the loadover load relay is connected in paral¬lel and no volt relay in series with the loadover load relay and no volt relay are both connected in series with the loadover load relay and no volt relay are both connected in parallel with the loadAns: a693. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?Providing laminations in armature coreProviding laminations in statorUsing non-magnetic material for frame

Using material of low hysteresis co-efficient for armaturecore material Ans: d694. Which of the following loss in a D.C. generator is dissipated in the form of heat?Mechanical lossCore lossCopper loss

All of the aboveAns: dWhich 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) Windagelosses Ans: bThe total losses in a well designed D.C. generator of 10 kW will be nearly100 W500 W1000 W1500 WAns: b697. The condition for maximum efficiency for a D.C. generator iseddy current losses = stray losseshysteresis losses = eddy current lossescopper losses = 0variable losses = constant lossesAns: d698. D.C. generators are normally designed for maximum efficiency aroundfull-loadrated r.p.m.rated voltage

all of theabove Ans: a

699. In a D.C. generator, the iron losses mainly take place inyokecommutatorarmature conductorsarmature rotorAns: dD.C. generators are installed near the load centres to reduce(a) iron losses(b) line losses(c) sparking

(d) coronalosses Ans: bThe purpose of retardation test on D.C. shunt machines is to find outstray losseseddy current lossesfield copper losseswindage lossesAns: a

702. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?Swinburne's testHopkinson's testField testBrake testAns: cHopkinson's test on D.C. machines is conducted at(a) no-load(b) part load(c) full-load

(d)overloadAns: cDuring rheostat braking of D.C. series motorsmotor is run as a generatormotor is reversed in direction

motor is run at reducedspeed Ans: a705. For which types of D.C. motor, dynamic braking is generally used ?Shunt motorsSeries motorsCompound motors

All of theabove Ans: d

706. Which method of braking is generally used in elevators ?PluggingRegenerative brakingRheostatic braking

None of the aboveAns: a707. In variable speed motora stronger commutating field is needed at low speed than at high speeda weaker commutating field is needed at low speed than at high speedsame commutating field is needed at low speed than at high speednone of the above is correctAns: b708. When the armature of a D.C. motor rotates, e.m.f. induced isself-induced e.m.f.mutually induced e.m.f.back e.m.f.none of the aboveAns: c

709. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed controldrum type controller is usedthree point starter is usedfour point starter is usedall above can be usedAns: a710. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opensthis will make armature to take heavy current, possibly burning it

(6) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stressesnothing will happen to motormotor will come to stopAns: 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 shortduration. We will select theseries motorshunt motorcompound motorany of the aboveAns: 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

series motorshunt motorcompound motorany of the aboveAns: c713. Which D.C. motor has got maximum self relieving property ?(a) Series motor(6) Shunt motorCumulatively compounded motor

Differentially compoundedmotor Ans: aIn the D.C. motor the iron losses occur in(a) the field(b) the armature(c) the brushes

(d) thecommutatorAns: bThe speed of a D.C. shunt motor is required to be more than full load speed. This is

possible byreducing the field currentdecreasing the armature currentincreasing the armature currentincreasing the excitation currentnone of the above methodsAns: a716. One D.C. motor another D.C. motor. The second D.C. motor when excited and drivenruns as a generatordoes not run as a generator

also runs as a motor comes to stop aftersometime Ans: a717. The insulating material for a

(a) low cost (b)high dielectric strength

(c) high mechanical strength (d) all of the aboveAns: d718. Which of the following protects a cable against mechanical injury ?BeddingSheathArmouringNone of the aboveAns: c

719. Which of the following insulation is used in cables ?Varnished cambricRubber

PaperAny of the aboveAns: d720. Empire tape isvarnished cambricvulcanised rubberimpregnated papernone of the aboveAns: a721. The thickness of the layer of insulation on the conductor, in cables,depends uponreactive powerpower factorvoltagecurrent carrying capacityAns: c722. The bedding on a cable consists of(a) hessian(b)any of the above

none of the aboveAns: c723. The insulating material for cables should(a) be acid proof (b) be non-inflammable(c) be non-hygroscopic (d) have all above propertiesAns: d724. In a cable immediately above metallic sheath _____ is provided.

(a)earthing connection (b) bedding

(c) armouring (d) none of the aboveAns: b725.

The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to

absence of harmonicsnon-existence of any stability limitsmaller dielectric lossabsence of ripplesnone of the aboveAns: c726. In case of three core flexible cable the colour of the neutral isblueblackbrown

none of the aboveAns: a

727. cables are used for 132 kV lines.High tensionSuper tensionExtra high tension

Extra supervoltage Ans: d728. Conduit pipes are normally used to protect _____ cables.unsheathed cablesarmouredPVC sheathed cablesall of the aboveAns: a729. The minimum dielectric stress in a cable is atarmourbeddingconductor surfacelead sheathAns: d730.

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: a731.

Dielectric strength of rubber is around

5 kV/mm15 kV/mm30 kV/mm

200 kV/mmAns: c732. Low tension cables are generally used upto200 V500 V700 V1000 VAns: d733. In a cable, the maximum stress under operating conditions is atinsulation layersheatharmourconductor surface

Ans: d734. High tension cables are generally used upto11kV

33kV66 kV

132 kVAns: a735. The surge resistance of cable is5 ohms20 ohms50 ohms

100 ohmsAns: c736. 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: a737. In the cables, the location of fault is usually found out by comparingthe resistance of the conductorthe inductance of conductorsthe capacitances of insulated conductorsall above parametersAns: c738. In capacitance grading of cables we use a ______ dielectric.compositeporoushomogeneous

hygroscopicAns: a739. Pressure cables are generally not used beyond11 kV33 kV66 kV

132 kVAns: c740. The material for armouring on cable is usuallysteel tapegalvanised steel wireany of the abovenone of the aboveAns: c741. Cables, generally used beyond 66 kV areoilS.L. type

beltedarmoured

Ans: a742. 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 14Ans: a743.

Solid type cables are considered unreliable beyond 66 kV because

insulation may melt due to higher temperatureskin effect dominates on the conduc¬torof corona loss between conductor and sheath material

there is a danger of breakdown of insulation due to thepresence of voids Ans: d744. If the length of a cable is doubled, its capacitancebecomes one-fourthbecomes one-halfbecomes doubleremains unchangedAns: c745. In cables the charging currentlags the voltage by 90°leads the voltage by 90°lags the voltage by 180°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 becomeone halfdoublefour timesnone of the aboveAns: a

747. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be5 kV/mm10 kV/mm15 kV/mm(d) 30 kV/mmAns: b748. 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 aboveAns: a749. The intersheaths in the cables are used to

minimize the stressavoid the requirement of good insulationprovide proper stress distributionnone of the aboveAns: c750. The electrostatic stress in underground cables issame at the conductor and the sheathminimum at the conductor and maximum at the sheathmaximum at the conductor and minimum at the sheathzero at the conductor as well as on the sheathnone of the aboveAns: c751. The breakdown of insulation of the cable can be avoided economically by the use ofinter-sheathsinsulating materials with different dielectric constantsboth (a) and (b)none of the aboveAns: c752. The insulation of the cable decreases withthe increase in length of the insulationthe decrease in the length of the insulationeither (a) or (b)none of the aboveAns: a753. A cable carrying alternating current hashysteresis losses onlyhysteresis and leakage losses onlyhysteresis, leakage and copper losses onlyhysteresis, leakage, copper and friction lossesAns: b754. In a cable the voltage stress is maximum atsheathinsulator(e) surface of the conductor

(d) core of the conductor Ans: d755. Capacitance grading of cable impliesuse of dielectrics of different permeabilitiesgrading according to capacitance of cables per km lengthcables using single dielectric in different concentrationscapacitance required to be introduced at different lengths to counter the effect

of inductancenone of the above

Ans: a756. Underground cables are laid at sufficient depthto minimise temperature stressesto avoid being unearthed easily due to removal of soilto minimise the effect of shocks and vibrations due to gassing vehicles, etc.for all of the above reasonsAns: c757. The advantage of cables over overhead transmission lines iseasy maintenancelow costcan be used in congested areas

can be used in high voltagecircuits Ans: c758. The thickness of metallic shielding on cables is usually0.04 mm0.2 to 0.4 mm(e) 3 to 5 mm

(d) 40 to 60 mm Ans: a759. Cables for 220 kV lines are invariablymica insulatedpaper insulatedcompressed oil or compressed gas insulatedrubber insulatednone of the aboveAns: c760.

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: d761.

If a power cable and a communication cable are to run parallel the minimum distance between

the two, to avoid interference, should be2 cm10 cm50 cm400 cmAns: c762. Copper as conductor for cables is used asannealedhardened and temperedhard drawn

alloy with chromium

Ans: a763. The insulating material should havelow permittivityhigh resistivityhigh dielectric strengthall of the aboveAns: d764. The advantage of oil filled cables ismore perfect impregnationsmaller overall sizeno ionisation, oxidation and formation of voidsall of the aboveAns: d765. The disadvantage with paper as insulating material isit is hygroscopicit has high capacitanceit is an organic material

none of the aboveAns: a766. 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 aboveAns: dIt is difficult to maintain oil filled cables.(a) Yes

(b)NoAns:aIn capacitance grading a homogeneous dielectric is used.(a) Yes

(b)NoAns:b

In congested areas where excavation is expensive and inconvenient 'draw insystem' of laying of underground cablesis often adopted.(a) Yes

(b)NoAns:a

Natural rubber is obtained from milky sap of tropical trees.Yes

NoAns:a

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