DC BASICS AND NETWORKS AND ELECTROMAGNETIC THEORY1. Two wires A and B of the same material and length l and 2l have radius r and 2r respectively. The ratio of their resistance will bea) 1:1b) 1:2c) 1:4d) 1:8ans: a

2. Pure metals generally havea) high conductivity and low temperature coefficientb) high conductivity and large temperature coefficientc) low conductivity and zero temperature coefficientd) low conductivity and high temperature coefficient ans: b

3. The temperature coefficient of resistance of a wire is 0.0008'C. If the resistance of the wire is 8 Ohm at 0'C , what is the resistance of the wire at 100'C?a) 8.64 Ohmb) 8.08 Ohmc) 7.92 Ohmd) 7.20 Ohmans: a

4. The insulation resistance of a cable of length is 1 MegaOhm.For a length of 100 km of same cable, the insulation resistance will bea) 1 MegaOhmb) 10 MegaOhmc) 0.1 MegaOhmd) 0.01 MegaOhmans: c

5. The hot resistance of the filament of a bulb is higher than the cold resistance because the temperature coefficient of the filament isa) negativeb) infinitec) zerod) positiveans: d

6. Four resistances 80 Ohm, 50 Ohm , 25 Ohm and R are connected in parallel. Current through 25 Ohm resistance is 4 A.Total current of the supply is 10 A. The value of R will be

a) 66.66 Ohmb) 40.25 Ohmc) 36.36 Ohmd) 76.56 Ohmans: c

7. Three parallel resistive branches are connected across a DC supply .What will be the ratio of the branch currents I1:I2:I3 if the branch resistances are in the ratio R1:R2:R3::2:4:6 ?a) 3:2:6b) 2:4:6c) 6:3:2d) 6:2:4ans: c.

8. Two resistors R1and R2 give combined resistance of 4.5 Ohm when in series and 1 Ohm when in parallel , the resistances area) 2 ohm and 2.5 ohmb) 1 ohm and 3.5 ohmc) 1.5 ohm and 3 ohmd) 4 and 0.5 ohmans: c

9. How are 500 Ohm resistors connected so as to give an effective resistance of 750 Ohm?a) Three resistors of 500 Ohm each , in parallelb) Three resistors of 500 Ohm each , in seriesc) Two resistors of 500 Ohm each , in paralleld) Two resistors of 500 Ohm, each , in parallel and the combination in series with another 500 Ohm resistor.ans: d

10. Which of the following does not use heating effect of electric current?a) Electric furnaceb) Geyserc) Electric Irond) Vacuum Cleanerans: d

11. Which of the following is not equivalent to Watts?a) amperes X voltsb) amperes X amperes X voltc) amperes/ voltd) joules per second

ans: c

12. A network consists of linear resistors and ideal voltage source. If the value of the resistors are doubled , then voltage across each resistor isa) halvedb) doubledc) increased four tinesd) not changedans: d

13. Three resistances each of R Ohm are connected to form a triangle. The resistance between any two terminals will bea) R ohmb) 3/2 ohmc) 3R ohmd) 2/3 ohmans: d

14. When an electric current flows through a conductor, its temperature rises. This is because ofa) mutual collisions between metal atomsb) mutual collisions between conducting electronsc) collisions between conduction electrons and atomsd) none of the aboveans: c

15. Two heaters , rated at 1000 W , each 250 V are connected in series across a 250 V , 50 Hz AC mains. The total power drawn from the supply would bea) 1000 Wb) 500 Wc) 250 Wd) 2000 Wans: b

16. Two incandescent light bulbs of 40 W and 60 W rating are connected in series across the mains. Thena) the bulbs together consume 100 Wb) the bulbs together consume 50 Wc) the 60 W bulb glows brighterd) the 40 W bulb glows brighterans : d

17. How many 200 W/ 220 V incandescent lamps connected in series would consume the same total power as a single 100W/ 220V incandescent lamp?

a) not possibleb) 2c) 3d) 4ans: b

18. A 100W bulb burns on an average of 10 hours a day for one week. The weekly consumption of energy will bea) 7b) 70c) 0.7d) none of the aboveans: a

19. A network has 4 nodes and 3 independent loops. What is the number of branches in the network?a) 5b) 6c) 7d) none of the aboveans: b

20. An electric circuit with 10 nodes and 7 branches will havea) 3 loop equationsb) 4 loop equationsc) 7 loop equationsd) none of the aboveans: b

21. A network has 10 nodes and 17 branches. . The number of different node pair voltage would bea) 7b) 9c) 45d) none of the aboveans: b

AC BASICS AND NETWORKS1. The rms value of a sine wave is 100 A. Its peak value isa) 70.7 Ab) 141 Ac) 150 Ad) 282.8 Aans: 2

2. The rms value of the resultant current in a wire which carries a dc current of 10 A and a sinusoidal alternating current of peak value 20 A isa) 14.1 Ab) 17.3 Ac) 22.4 Ad) none of the aboveans: b

3. A boiler at home is switched on to the AC mains supplying power at 230 V, 50 Hz. The frequency of instantaneous power consumed isa) 0 Hzb) 50 Hzc) 100 Hzd) 150 Hzans: c

4. Unit of inductive reactance isa) Henryb) millihenryc) Wbd) Ohmans: d

5. A 10 mH inductor carries a sinusoidal current of 1A rms at a frequency of 50 Hz. The average power dissipated by the indicator isa) 0 Wb) 0.25 Wc) 0.5 Wd) 1.0 Wans: a

6. A circuit component that opposes the change in circuit voltage isa) resistanceb) capacitancec) inductanced) all of the aboveans: b

7. The reactance offered by a capacitor to AC of frequency 50 Hz is 10 ohm. If the frequency is increased to 100 Hz , reactance becomesa) 20 ohm

b) 5 ohmc) 2.5 ohmd) 30 ohmans: b

8. The pf of a practical inductor isa) unityb) zeroc) laggingd) leadingans: c

9. The power factor of an ordinary electric bulb isa) zerob) unityc) slightly more than unityd) slightly less than unityans: d

10. A 2-terminal network consists of one of the RLC elements. The element is connected to ans ac supply. The current through the element is I A. When an inductor is inserted in series between the source and the element , the current through the element becomes 2I A . What is the element?a) A resistorb) An inductorc) A capacitord) cannot be a single elementans: c11. Unit of reactive power isa) VAb) wattc) VARd) ohmans: c

12. An ac source of 200V rms supplies active power of 600 W and reactive power of 800 VAR. The rms current drawn from the source isa) 10 Ab) 5 Ac) 3.75 Ad) 2.5 Aans: b

13. With the increase in applied frequency , the dielectric loss in a material willa) increaseb) decreasec) remains constantd) becomes zeroans: a

14. In a ac series RLC circuit , the voltage across R and L is 20 V, the voltage across L and C is 9 V and voltage and voltage across RLC is 15 V , What is the voltage across C?a) 7Vb) 12 Vc) 16 Vd) 21 Vans: a

15. The quantity (2 + j9) represents the resistive and reactive components of current drawn by an ac circuit. The phase angle between the applied voltage and current isa) 41.4'b) 53.13'c) 36.87'd) 46.86'ans: c

16. Under the condition resonance in R-L-C series circuit, the pf of the circuit isa) 0.5 laggingb) 0.5 leadingc) unityd) zeroans: c

17. In a series RLC circuit at resonance , the magnitude of voltage developed across the capacitora) is always zerob) can never be greater that the input voltagec) can be greater than the input voltage however, it is 90 degrees out of phase with the input voltaged) can be greater than the input voltage and is in phase with the input voltage.ans: c

18. A series R-L-C circuit , the maximum voltage across the capacitor occurs at a frequencya) double the resonant frequencyb) equal to resonant frequencyc) below the resonant frequencyd) none of the above

ans: c

19. In a series R-L-C circuit , the voltage across inductance will be maximuma) at resonant frequencyb) just after resonant frequencyc) just before resonant frequencyd) just before and after resonant frequencyans: b

20. For a series R-L-C circuit , the power factor at the lower power frequency isa) 0.5 laggingb) 0.5 leadingc) unityd) 0.707 leadingans: d21. Q-factor of as series R-L-C circuit possessing resonant frequency of 10 Hz and bandwidth of 5 Hz isa) 0.5b) 2c) 2.5d) 50ans: b

22. When Q-factor of a circuit is high , thena) power factor of the circuit is highb) impedance of the circuit is highc) bandwidth is larged) none of the aboveans: b

23. A high Q coil hasa) large bandwidthb) high lossesc) low lossesd) flat responseans: c

24. A coil is tuned to resonance at 500 kHz with a resonating capacitor of 36 pf at 250 kHz , the resonance is obtained with resonating capacitor of 160 pf .What is the self-capacitance of the coil?a) 2.66 pfb) 5.33 pfc) 8 pfd) 10.66 pf

ans: b

25. A R-L-C resonant circuit has a resonance frequency of 1.5 MHz and a bandwidth of 10kHz . If c= 150pf, then the effective resistance of the circuit will bea) 29.5 ohmb) 14.75 ohmc) 9.4 ohmd) 4.7ohmans: d

ANALOG ELECTRONICS1.The emitter of a transistor is generally doped the heaviest because ita) has to dissipate maximum powerb) has to supply the charge carriersc) is the first region of the transistord) must posses low resistanceans: b

2. An emitter is a bipolar junction transistor is doped much more heavily than the base as it increases thea) emitter efficiencyb) Base transport factorc) forward current gaind) all the aboveans: d

3. The impurity commonly used for realizing the base region of a silicon n-p-n transistor isa) Galliumb) indiumc) Borond) Phosphorusans: c

4. In a properly biased N-P-N transistor , most of the electrons from the emittera) pass to the collector through the baseb) recombine with holes in the basec) recombine with holes in emitter itselfd) are stopped by the function betterans: a

5. For an npn bipolar transistor, what is the main stream of current in the base region ?a) Drift of holes

b) Diffusion of holesc) Drift of electronsd) Diffusion of electronsans: d

6. The DC current gain of BJT is 50. Assuming that the emitter injection efficiency is 0.995, the base transport factor isa) 0.980b) 0.985c) 0.990d) 0.995ans: b

7. If for a silicon npn transistors , the base-to-emitter voltage is 0.7 V and the collector-to-base Voltage is 0.2 V , then the transistor is operating in thea) normal active modeb) saturation modec) inverse active moded) cutoff modeans: a

8. Ebers-model of a transistor represents two diodesa) in seriesb) in parallelc) back-to-backd) none of the aboveans: c

9. In a transistor , the reverse saturation current Icoa) doubles for every 10 deg/C rise in temperatureb) doubles for every 1 deg/C rise in temperaturec) increases linearly with temperatured) decreases linearly with temperatureans: a

10. The phenomenon known as "Early Effect" in a bipolar transistor refers to a reduction of the effective base-width caused bya) electron hole recombination at the timeb) the reverse biasing of the base-collector junctionc) the forward biasing of emitter-base junctiond) the early removal of stored base charge during saturation-to-cutoff switchingans: b

11. Notch is also called asa) band-pass filterb) low-pass filterc) high-pass filterd) narrow-band reject filterans: d

12. The filter which exhibits ac equiripple in the pass-band and monotonic characteristic in stop band isa) Buttorworthb) Chebyshevc) Besseld) Ellipticans: a

13. A multiplier which can accept input voltages of either polarity and can produce output voltage of both polarities is calleda) Bi-quadrant multiplierb) four quadrant multiplierc) two quadrant multiplierd) one quadrant multiplierans: c

14. A multiplier is derived using two logarithmic amplifiers and and antilog amplifier . One more section required isa) multiplierb) adderc) subtractord) dividerans: b

15. A frequency multiplier usually operates ina) push-pullb) class Ac) class Bd) class Cans: d

16. FSK demodulation is an application ofa) PLLb) timerc) BPF

d) none of the aboveans: a

17. An oscillator whose frequency is changed by a variable dc voltage is known asa) a crystal oscillatorb) a VCOc) an Armstrong oscillatord) a piezoelectric deviceans: b

18. The integrated circuit chip NE/SE 566 is aa) Schmitt triggerb) power amplifierc) video amplifierd) voltage controlled oscillatorans: d

19. For a step input , the output of an integrator isa) a pulseb) a triangular waveformc) a spiked) a rampans: d

20. The damping factor of a second order active low pass filter to give butterworth response isa) 1.732b) 1.414c) 0.707d) none of the aboveans: b

ELECTRONIC COMPONENTS AND DEVICES1. The color code of a 1 kiloohm resistance isa) black , brown , redb) red, brown, brownc) brown, black, redd) black, black , redans. c

2. An electron with velocity u is placed in an electric field E and magnetic field B. The force experienced by the electron is given bya) -eE

b) -eu X Bc) -e(u X E + B)d) -e(E + u X B)ans. d

3. The primary reason for the widespread use of Silicon semiconductor device technology isa) abundance of Silicon on the surface of Earth.b) larger bandgap of Silicon in comparison to Germanium.c) favourable properties of Silicon-dioxide (Sio2).d) lower melting point.ans. a

4. A Silicon wafer has 100 nm of oxide on it and is inserted in a furnace at a temperature above 1000 degree centigrade for further oxidation in dry oxygen. The oxidation rate isa) independent of current , oxide thickness and temperature.b) independent of current, oxide thickness but depends on temperature.c) slows down as the oxide grows.d) zero as the existing oxide prevents further oxidations.ans. d

5. The band gap of silicon at room temperature isa) 1.3 eVb) 0.7 eVc) 1.1 eVd) 1.4 eVans. c

6. n-type silicon is obtained by doping silicon witha) Germaniumb) Aluminiumc) Borond) Phosporousans. d

7. Which of the following is true ?a) A silicon wafer heavily doped with boron is a p+ substrate.b) A silicon wafer lightly doped with boron is a p+ substrate.c) A silicon wafer heavily doped with Arsenic is a p+ substrate.d) A silicon wafer lightly doped with Arsenic is a p+ substrate.ans. a

8. The concentration of minority carriers in an extrinsic semiconductor under equilibrium is

a) directly proportional to the doping concentration.b) inversely proportional to the doping concentration.c) directly proportional to the intrinsic concentration.d) inversely proportional to the intrinsic concentration.ans. b

9. Under low level injection assumption, the injected minority carrier current for an extrinsic semiconductor is essentially thea) diffusion currentb) drift currentc) recombination currentd) induced currentans. a

10. The majority carriers in an n-type semiconductor have an average drift velocity in a direction perpendicular to a uniform magnetic field B. The electric field E induced due to Hall effect acts in the direction .a) v X Bb) B X vc) along vd) opposite to vans. B

11. The depletion region or space charge region or transition region in a semiconductor P-N junction diode hasa) electron and holes.b) positive ions and electrons.c) positive ions and negative ions.d) no ions, electron or holes.ans. c

12. In a p+ n junction diode under reverse bias, the magnitude of electric field is maximum ata) the edge of the depletion region on the p-side.b) the edge of the depletion region on the n-side.c) the p+n junction.d) the centre of the depletion region on the n-side.ans. c

13. A p-n junction has a built-in potential of 0.8 V. The depletion layer width at a reverse bias of 1.2V is the 2 micrometer. For a reverse bias of 7.2V , the depletion layer width will bea) 4 micrometerb) 4.9 micrometer

c) 8 micrometerd) 12 micrometerans. a

14. At 300 K for a diode current of 1mA , a certain germanium diode requires a forward bias of 0.1435 V, whereas a certain silicon diode requires a forward bias of 0.718 V, Under the conditions stated above , the closest approximation of the ratio of reverse saturation current in germanium diode to that in silicon diode isa) 1b) 5c) 4 x 10³d) 8 x 10³ans. c

15. A silicon PN junction at a temperature of 20⁰C has a reverse saturation current of 10 pico-Amperes (pA). The reverse saturation current at 40⁰C for same bias is approximatelya) 30 pAb) 40 pAc) 50 pAd) 60 pAans. b

16. Which of the following is not associated with a p-n junction ?a) Junction Capacitanceb) Charge Storage-Capacitancec) Depletion Capacitanced) Channel Length Modulation.ans. d

17. As the temperature is increased, the voltage across a diode carrying a constant currenta) increasesb) decreasesc) remains constant.d) may increase or decrease depending on the doping levels in the junction.ans. b

18. Choose proper substitutes of X and Y to make the following statement correct. Tunnel diode and Avalanche diode are operated in X bias and Y bias respectivelya) X- reverse ,Y-reverseb) X-reverse, Y -forwardc) X-forward, Y- reversed) X-forward, Y-forward

ans. c

19. Consider the following assertions.S1- For zener effect to occur, a very abrupt junction is required.S2- For quantum tunneling to occur , a very narrow energy barrier is required.which of the following is correct?a) Only S2 is true.b) S1 and S2 are both true but S2 is not a reason for S1c) S1 and S2 are both true and S2 is a reason for S1.d) Both S1 and S2 are false.ans. a

20. A dc power supply has a no-load voltage of 30 V, and a full-load voltage of 25 V at a full load-current of 1A. Its output resistance and load regulation , respectively area) 5 ohm and 20 %b) 25 ohm and 20%c) 5 ohm and 16.7%d) 25 ohm and 16.7 %ans. b

POWER SYSTEMS1. For low head and high discharge the hydraulic turbine used isa) Francis turbineb) Kaplan turbinec) Pelton wheeld) none of the aboveans: b

2. A Kaplan turbine isa) In ward flow, impulse turbineb) Outward flow reaction turbinec) A high head mixed flow turbined) Low head axial flow turbineans: d

3. An hydro-graph indicatesa) The discharge at any time during the period under considerationb) The max. and min. runoff during the periodc) The average run off during the periodd) all the aboveans: d

4. As compared to steam-station ,hydro-electric stations have :a) More cost of installationb) Less maintenance and fuel costc) both (a) and (b)d) Low depreciation charges.ans: c

5. The rotor used in alternators of hydro-electric station isa) Cylindrical rotorb) Salient pole rotorc) Non salient pole rotord) Round rotor with ac excitationans: b

6. The cost of fuel transportation is minimum in ______ plant.a) Thermalb) Nuclearc) Hydrod) Dieselans: c

7. Which of the following generating stations has minimum running cost.a) Thermalb) Nuclearc) Hydrod) none of theseans: c

8. Which of the following plants have the highest capital costa) Nuclearb) Dieselc) Thermald) noneans: a

9. For harnessing low variable water heads, the suitable hydraulic turbine with high percentage of reaction and runner adjustable vanes isa) Kaplanb) Francisc) Peltond) Impellerans: a

10. In a Thermal power plant, the feed water coming to the economizer is heated usinga) H.P. steamb) L.P. steamc) direct heat in the furnaced) flue gasesans: d

11. In thermal power plants, the pressure in the working fluid cycle is developed bya) Condenserb) Super heaterc) feed waterd) turbineans: d

12. Which material is used in controlling chain reaction in av nuclear reactor?a) Thoriumb) Heavy waterc) Borond) Berylliumans: b

13. When a fixed amount of power is transmitted, the efficiency of transmission increases whena) Voltage decreases, power factor remains constantb) voltage increases, power factor increasec) voltage decreases, power factor decreasesd) voltage constant , power factor decreasesans: b

14. The surge impedance of 0.400km long OH line is 400 ohm for 200 km length of the same line , the surge impedance will bea) 200 ohmb) 800 ohmc) 400 ohmd) 100 ohmans: c

15. The insulation level of a 400 EHV OH transmission line is decided on the basis ofa) lightening voltageb) switching over voltagec) corona inception voltaged) radio and TV interference

ans: b

16. Bundled conductors are employed to improve thea) appearance of the transmission lineb) mechanical stability of the linec) decrease system stabilityd) increase the short circuit currentans: c

17. An OH line having a surge impedance of 400 ohm is connected in series with an underground cable having a surge impedance of 100 ohm . If a surge of 50 Kv travels from the line end towards the line cable junctions, the value of the transmitted voltage wave at the junction isa) 30 Kvb) 20 Kvc) 80 Kvd) -30 Kvans: b

19. The load carrying capability of a long AC transmission line isa) always limited by the conductor sizeb) limited by stability considerationsc) reduced at low anbrent temperaturesd) decreased by the use of bundled conductors of single conductors.ans: b

20. Corona losses are minimized whena) corona size is reducedb) smooth conductor is releasedc) sharp points are provided in the hardwared) current density in conductors is reducedans: b

21. The corona loss on a particular system at 50HZ is 1kw/km/ph. The rocona loss at 60 HZ isa) 1kw/ph/kmb) 0-83 kw/km/phc) 1.2 kw/km/phd) 1.13 kw/km/phans: d

22. A loss-less radial transmission line with surge impedance loadinga) takes negative VAR at sending end and zero VAR at receiving endb) take positive VAR at sending end and zero VAR at receiving end

c) has flat voltage profile and unity power factor at all points along itd) has sending end voltage higher than receiving end voltage and unity power factor at sending endans: c

23. Consider along , two wire line composed of solid round conductors. The radius of both conductors is 0.25 cm and the distance between there centers is 1m . If this distance is doubled, then the inductance per unit lengtha) doublesb) halvesc) increase but does not doubled) decreases but not halveans: c

24. A long wire composed of a smooth round conductor runs above and parallel to the ground. A high voltage exists between the conductor and the ground . The max electric stress occurs at.a) the upper surface of the conductorb) the lower surface of the conductorc) the ground surfaced) none of the aboveans: b

25. Bundled conductors are mainly used in high voltage OH transmission lines toa) reduce transmission line lossesb) increase mechanical strength of the linec) reduce coronad) reduce sagans: c

DC MACHINES1. The developed electromagnetic force and/or torque in electro mechanical energy conversion system act in a direction that tendsa) to increase the stored energy at constant fluxb) to decrease the stored energy at constant fluxc) to decrease the coenergy at constant mmf.d) to decrease the stored energy at constant mmfans: b

2. For a linear electromagnetic circuit, the following statement is truea) Field energy is equal to the coenergyb) Field energy is greater than the coenergyc) Field energy is lesser than the coenergyd) Coenergy is zero

ans: a

3. In an electromechanical energy conversion device, the developed torque depends upona) stator field strength and torque angleb) stator field and rotor field strengthsc) stator field and rotor field strengths and torque angled) stator field onlyans: c

4. In electro mechanical energy conversion devices , a small air gap is left between the stator and rotor in order toa) reduce the reluctance of the magnetic pathb) increase flux density in the air gapc) permit mechanical clearanced) none of the aboveans: c

5. A rotating electrical machine having its self inductance of both stator and rotor winding's, independent of rotor position will definitely not developa) starting torqueb) synchronizing torquec) hysteresis torqued) reluctance torqueans: b

6. A circular metallic disc is placed in a vertical magnetic field of constant induction in the downward direction. If the disc is rotated in a horizontal plane , the emf induced will bea) zerob) constant independent of disc sizec) increasing radically in the outward directiond) decreasing radically in the outward directionans: a

7. The emf induced in a conductor rotating in a bipolar field isa) dcb) acc) dc and ac bothd) none of theseans: b

AC MACHINES 11. The basic function of a transformer is to change

a) the level of the voltage.b) the power levelc) the power factord) the frequencyans: a

2. In an ordinary transformer which of the following does not changea) voltageb) currentc) frequencyd) all the aboveans: c

3. The efficiency of a power transformer is arounda) 50%b) 60%c) 80%d) 95%ans: d

4. An ideal transformer does not changea) voltageb) powerc) currentd) none of the aboveans: b

5. For an ideal transformer the winding's should havea) maximum resistance on primary side and least resistance on secondary sideb) least resistance on primary side and maximum resistance on the secondary sidec) equal resistance on primary and secondary sidesd) no ohmic resistance on either sideans: d

6. The core flux in transformer depends mainly ona) supply voltageb) supply voltage and frequencyc) supply voltage, frequency and loadd) supply voltage and load but independent of frequencyans: b

7. A transformer steps up the voltage by a factor 100. The ratio of current in the primary to that in the secondary isa) 1b) 100c) 0.01d) 0.1ans: b

8. If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced 50% , the maximum core flux density willa) change to three times the original value.b) change to 1.5 times the original valuec) change to 0.5 times the original valued) remain the same as the original valueans: a

9. If the supply frequency of a transformer is increased , keeping the supply voltage constant, thena) both magnetizing component and core loss component of current will decreaseb) both magnetizing component and core loss component of current will increasec) magnetizing component of current will increase while core loss component of current will decreased) magnetizing component of current will decrease while core loss component of current will increase.ans: a

10. Primary winding of a transformer comprises of two identical winding's in parallel. If one winding's is removed , magnetizing current will bea) halvedb) the samec) doubled) increased four timesans: c

11. The core flux of a practical transformer with a resistance loada) is strictly constant with load changesb) increases linearly with loadc) increases as the square root of the loadd) decreases with increase of loadans: a

12. In a transformer , zero voltage regulation at full load isa) not possibleb) possible at unity power factor loadc) possible at leading power factor load

d) possible at lagging power factor loadans: c

13. A single phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor isa) 86.7%b) 88.26 %c) 88.9%d) 87.8%ans: d

14. The main purpose of performing open-circuit on a transformer is to measure itsa) copper lossb) core lossc) total lossd) insulation resistanceans: b

15. The desirable properties of transformer core material area) low permeability and low hysteresis lossb) high permeability and high hysteresis lossc) high permeability and low hysteresis lossd) low permeability and high hysteresis lossans: c

16. The all -day efficiency of a transformer depends primarily ona) its copper lossb) the amount of loadc) duration of loadd) both b and cans: d

17. The use of higher flux density in the transformer designa) reduces the weight per KVAb) increases the weight per KVAc) has no relation with the weight of transformerd) none of the aboveans: a

18. What does the the use of higher flux density in the transformer designa) Increase the weight per KVA

b) Decrease in weight per KVAc) Reduced iron lossesd) Reduced copper lossesans. b

19. Cores of large power transformers are made from which one of the following ?a) Hot-rolled steelb) Cold-rolled non-grain oriented steel.c) Cold-rolled grain oriented steeld) Ferrite.ans. c

20. Grain oriented laminated sheel steel in transformer reducesa) copper lossb) eddy current lossc) hysteresis lossd) none of the aboveans. C

SWITCHGEAR AND PROTECTION 321. A lightning stroke discharges impulse current of 10 kA (peak) on a 400 kV transmission line having surge impedance of 250 ohm. The magnitude of transient over voltage travelling waves in either direction assuming equal distribution from the point of lightning strike will bea) 1250 kVb) 1650 kVc) 2500 kVd) 2900 kVans. a

22. The insulation strength of an EHV transmission line is mainly governed bya) load power factorb) switching overvoltagesc) harmonicsd) coronaans. b

23. Steady-state stability of a power system is the ability of the power system toa) maintain voltage at the rated voltage levelb) maintain frequency exactly at 50Hzc) maintain a spinning reserve margin at all times.d) maintain synchronism between machines and on external tie lines.ans. d

24. The load carrying capability of a long ac transmission line isa) always limited by the conductor sizeb) limited by stability considerations.c) reduced at low ambient temperatures.d) decreased by the use of bundled conductors of single conductors.ans. b

25. An 800 kV transmission line is having per phase line inductance of 1.1 mH/km and per phase line capacitance of 11.68 nF/km. Ignoring the length of the line , its ideal power transfer capability in MW isa) 1204 MWb) 1504 MWc) 2085 MWd) 2606 MWans. c

26. An 800 kV transmission line has a maximum power transfer capacity of P. If it is operated at 400 kV with the series reactance unchanged, then maximum power transfer capacity is approximatelya) Pb) 2Pc) P/2d) P/4ans. d

27. A round rotor generator with internal voltage E1=2.0 pu and X=1.1 pu is connected to a round rotor sysnchronous motor with internal voltage E2= 1.3 pu and X= 1.2 pu. The reactance of the line connecting the generator supplies 0.5 pu power, the rotor angle difference between the machines will bea) 57.42 degreesb) 1 degreec) 32.58 degreesd) 122.58 degreesans. c

28. The pu parameters for a 500 MVA machine on its own base are: inertia , M= 20 pu ; reactance ,X= pu. The pu values of inertia and reactance on 100 MVA common base, respectively, area) 4, 0.4b) 100, 10c) 4, 10d) 100,0.4ans. d

29. A power station consists of two synchronous A and B of ratings 250 MVA and 500 MVA with inertia 1.6 and 1.0 pu respectively on their own base MVA ratings. The equivalent pu inertia constant for the system on 100 MVA common base isa) 2.6b) 6.15c) 1.625d) 9ans. d

30. A shunt reactor of 100 MVAr is operated at 98% of its rated voltage and at 96% of its rated frequency. The reactive power absorbed by the reactor isa) 98. MVArb) 10.402 MVArc) 96.04 MVArd) 100 MVArans. D

31. A 3-phase 11kV generator feeds power to a constant power unity power factor load of 100 MW through a 3-phase transmission line. The line-to-line voltage at the terminals of the machine is maintained constant at 11 kV. The per unit positive sequence impedance of the line based on 100 MVA and 11 KV is j0.2. The line-to-line voltage at the load terminals is measured to be less than 11kV. The total reactive power to be injected at the terminals of the load to the increase the line-to-line voltage at the load terminals to 11 kV isa) 100 MVARb) 10.1 MVARc) -100 MVARd) -10.1 MVARans. d

A generator feeds power to an infinite bus through a double circuit transmission line. A 3-phase fault occurs at the middle point of one of the lines. The infinite bus voltage is 1 pu, the transient internal voltage of the generator is 1.1 pu and the equivalent transfer admittance during fault is 0.8 pu. The 100 MVA generator has an inertia constant of 5 MJ/MVA and it was delivering 1.0 pu power prior of the fault with rotor power angle of 30⁰ . The system frequency is 50 Hz.

32. The initial accelerating power (in pu) will bea) 1.0b) 0.6c) 0.56d) 0.4ans. c

33. If the initial accelerating power is Xpu, the initial acceleration in electrical degrees/sec , and the inertial constant in MJ-sec/electrical degrees respectively will bea) 31.4X,18b) 1800X, 0.056c) X/1800 , 0.056d) 3/3.14, 18ans. b

34. In load-flow analysis , the load connected at a bus is represented asa) constant current drawn from the bus.b) constant impedance connected at the bus.c) voltage and frequency dependent source at the bus.d) constant real and reactive power drawn from the bus.ans. d

35. Gauss-Siedel interative method can be used for solving a set ofa) linear differential equations only.b) linear algebraic equations only.c) both linear and nonlinear algebraic equations only.d) both linear and nonlinear differential equations only.ans. b

36. The Gauss-Siedel load flow method has the following disadvantages. Tick the incorrect statementsa) Unreliable convergenceb) slow convergencec) choice of slack bus affects convergence.d) A good initial guess for voltages is essential for convergence.ans. b

37. A power system consists of 300 buses out of which 20 buses are generator bus, 25 buses are ones with reactive power support and 15 buses are the ones with fixed shunt capacitors. All the other buses are load buses. It is proposed to perform a load flow analysis in the system using Newton-Rapson method. The size of the Newton-Rapson Jacobian matrix isa) 553 X 553b) 540 X 540c) 555 X 555d) 554 X 554ans. b

38. If the reference bus is changed in two load flow buses with same system data and power obtained for reference bus taken as specified P and Q in the latter runa) the system losses will be unchanged but complex bus voltages will change.

b) the system losses will change but complex bus voltages remain unchanged.c) the system losses as well as complex bus voltages will change.d) the system losses as well as complex bus voltages will be unchanged.ans. A

ELECTRICAL MACHINE DESIGN1. For a soft magnetic material there will bea) steeply rising magnetization curve.b) relatively narrow and small hysteresis loop.c) less energy loss per cycle of magnetization.d) all the above.

2. Silicon content in iron lamination is kept within 5% as ita) increases hysteresis loss.b) increases cost.c) makes the material brittle.d) reduces the curie point.ans: c

3. For under frequency operation the eddy current lossa) decreases.b) increases.c) remains unchanged.d) cannot be predicted.ans: a.

4. What is the suitable shape of plunger magnet to give almost flat force-stroke characteristics?a) Flat faced .b) Conical.c) Stepped.d) Tapered.ans: d.

5. In a dc machine " contraction coefficient" is used to take into account the reduction ofa) air-gap area due to armature slots.b) iron losses in the teeth due to lower tooth density.c) armature mmf due to armature slots.d) torque due to ventilating duets.ans: a

6. Carter's coefficient is applicable for estimating

a) requirements of air-gap mmf.b) flux distribution in air gap.c) length of air gap.d) no-load loss.ans: a

7. A lap wound dc machine has 400 conductors and 8 poles. The voltage induced per conductor is 2 volts. The machine generates a voltage ofa) 100 Vb) 200 Vc) 400 Vd) 800 Vans: a

8. The yoke of a dc machinea) must be made of magnetic material.b) should preferably be made of magnetic material but can be of non-magnetic material.c) must be made of non-magnetic material.d) is partially made of magnetic material and partially made of non-magnetic material.ans: a.

9. The pole shoes of a dc machinesa) are always laminated.b) are never laminated.c) are sometimes laminated.d) are partially laminated.ans: a

10. Poles of a dc machines are often laminated toa) reduce pulsation loss.b) reduce armature reaction.c) reduce iron weight.d) dissipate more heat.ans: a.

ELECTRICAL ENGINEERING MATERIALS1. Total number of electrons that can be accommodated in various electron states in a valence band of a given solid is equal toa) atomic number of the solid.b) half the number of atoms in the solid.c) the number of atoms in the solid.d) twice the number of atoms in the solid.

ans: a.

2. Vacant lattice sites in the halide crystals causea) plastic deformation and ionic conductivity.b) transparency and diffusion.c) diffusion and ionic conductivity.d) plastic deformation and transparency.ans: c.

3. For which of the following materials , is the Hall coefficient zero?a) Metal.b) Insulator.c) Intrinsic semiconductor.d) Alloy.ans: c.

4. Principle of Hall effect is used in the construction of which one of the following?a) Ammeter.b) Voltmeter.c) Galvanometer.d) Gauss meter.ans: d.

5. According to the Wiedemann-Franz law the ratio of thermal conductivity of electrical conductivity of a conductor isa) independent of temperature.b) directly proportional to temperature.c) inversely proportional to temperature.d) inversely proportional to square of temperature.ans: b.

6. The correct sequence of increasing order of electrical resistivity of the given materials isa) diamond, doped germanium , silicon, gold.b) gold , silicon, doped germanium , diamond.c) gold , doped germanium , silicon, diamond.d) gold , diamond , silicon, doped germanium.ans: c.

7. What is the correct arrangement of the following alloys in the decreasing order of resistivity?a) German silver- constantan- monel metal.b) German silver-monel metal- constantan.c) constantan-monel model- German silver.

d) constantan - German silver- monel metal.ans: d.

8. In metals, resistivity is composed of two parts : one part is characteristic of the particular substance. The other part is due toa) applied voltage.b) crystal imperfections.c) applied magnetic field.d) supplied thermal energy.ans: b.

9. Which one of the following is correct? As frequency increases, the surface resistance of metala) decreases.b) increases.c) remains unchanged.d) varies in an unpredictable manner.ans: b.

10. The conductivity of a conducting material on being subject to critical magnetic field changes toa) normal state.b) unstable state.c) temperature-independent state.d) temperature-dependent state.ans: a.

CONTROL SYSTEMS1. The most commonly used input signal in control system isa) step functionb) ramp or velocityc) accelerating functiond) all the aboveans: a

2. What is the characteristic of a good control system?a) Sensitive to parameter variationb) insensitive to input commandsc) Neither sensitive to parameter variation nor sensitive to input commandsd) Insensitive to parameter variation but sensitive to input commandsans: d

3. Linear system obeysa) principle of maximum power transfer

b) reciprocity principlec) principle of superpositiond) all the aboveans: d

4. If a linear time invariant system is excited by a true random signal like white noise, the output of the linear system will have which of the following properties ?a) output will be a white noiseb) output will be periodicc) output will not be randomd) output will be correlated or colored noise.ans: c

5. A system can be completely described by a transfer if it isa) nonlinear and continuousb) linear and time-varyingc) non-linear and time-invariantd) linear and time-invariantans: d

6. A function of one or more variables which conveys information on the nature of physical phenomenon calleda) noiseb) interferencec) systemd) signalans: d

7. If the initial conditions for a system are inherently zero , what does it physically mean?a) The system is at rest but stores energyb) The system is working but does not store energyc) The system is at rest or no energy is stored in any of its partsd) The system is working with zero reference inputans: d

8. In a control system, the use of negative feedbacka) eliminates the chances of instability.b) increases the reliability.c) reduces the effects of disturbance and noise signals in the forward path.d) increases the influence of variations of component parameters on the system performance.ans: c

9. which one of the following effects in the system is NOT caused by negative feedback?a) Reduction in gainb) increase in bandwidth.c) increase in distortion.d) reduction in output impedance.ans: c

10. In a speed control system , output rate feedback is used toa) limit the speed of motor.b) limit the acceleration of the motorc) reduce the damping of the systemd) increase the gain margin.ans: c