Civil Service - Electrical Engineering Prelims 1998-2007

C.S.E Pre-1998

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ELECTRICAL ENGINEERING 1.

The open-loop transfer function of the control system shown in the figure is

10 s  s  1 s  2  b. 0.6 6 c. s  s  1 s  2 

a.

10 s  3s 2  2s  6 If the single flow graph shown in the given figure has M number of forward paths and P number of individual loops, then d.

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a. M = 6, P = 6 b. M = 6, P = 4 c. M = 4,P = 6 d. M = 4, P = 4 The impulse response of a system is given 1 by c(t)  e t /2 Which one of the 2 following is it’s unit step response? a. 1  e 1/2t b. 1  e t c. 2  e t d. 1  e 2t If the open-loop transfer function of a feedback system is given by K G s H s  the s  s  2   s 2  2s  5 centroid of the as motes will be a. -1,0 b. 1.0 c. 0,-1 d. 0,1

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The first element of each of the rows of a Routh-Hurwitz stability test showed the sign as follows: Rows I II III IV V VI VIII Sings + – + + + + The number of roots of the system lying in the right half of s plane is a. 2 b. 3 c. 4 d. 5 6. The performance specifications for unity feed control system having an open-loop transfer function K are G s s  s  1 s  2  1. Velocity error coefficient 1 KV  10sec 2. Stable closed-loop operation The value of K, satisfying the above specification is a. K>6 b. 690° and P2 max  < 90° d. P1 max occur at  < 90° and P2 max at  < 90° Consider the following expression: V  f1  x  rt   f 2  x  rt 

Where f1 and f2 represent two traveling waves on a transmission line. In this case a. Both waves travels in the positive direction of x b. Both waves travel in the negative direction of x c. Wave f2 travels in the positive direction of x but wave f2 travels in the negative direction of x 78. For reducing tower foot in resistance, it is better to employ a. Chemical and counterpoise b. Chemical and ground rods c. Ground rots and counterpoise d. Chemical, gou8nd rods and counterpoise 79. A suspension type insulator has three units with self-capacitance C and ground capacitance of 0.2 C having a string efficiency of a. 78% b. 80% c. 82% d. 84% 80. A bulled conductor line compared to a single conductor line (With same conductor cross-sectional area and same meant distance between conductors) has Self GMD Mutual GMD Per phase inductance a. Lower Nearly same Higher b. Higher Lower Nearly same c. Higher Nearly same Lower d. Lower Higher Higher 81. In a 14-bus power system network, three are 5 voltage controlled buses. The size of the jacobiam matrix useful for power flow analysis will be a. 16 × 16 b. 23 × 23

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c. 21 × 21 d. 8 × 8 A thyrite lighting arrester has a. Inverse resistance characteristics b. A gap c. Efficient earthling d. A combination of inverse resistance characteristics and gap Differential protection of a generator makes use of the principal that under normal conditions, the current/currents a. At the neutral end of a phase winding is zero b. In each of the phase winding is identical c. At both ends of the phase winding are equal d. At the two ends of the phase winding are unequal the reactance relay is essentially The reactance realy is essentially a. An over-voltage realy with current restraint b. An over-current realy with directionally restraint c. A directional realy with voltage restraint d. A directional realy with current restraint Severe over-voltages are produced during arcing faults in a power system with the neutral a. Isolated b. Solidly Earthed c. Earthed through a low resistance d. Earthed through an inductive coil In HVCD transmission system, rectifier firing angle  is kept near a. 0° b. 15° c. 30° d. 90° A two-bus system is shown in the given figure. When 100 MW is transmitted from plant 1 to the load, the transmission loss is 10MW. The incremental; fuel costs of the dc1 two plants are  0.02 P1  16 and dP1 dc 2  0.04 P2 20 . dP2 The optimum distribution of total load of 260 MW between the two plants when losses are included but not coordinated is

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P2 P1 a. 300MW 50MW b. 240MW 20MW c. 130MW 130MW d. 220MW 60MW Assertion (A): The system with transfer function 10  s  12  G s  s  s  2  s  3 Reason (R): It has a zero on the right half of the s-plane. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): The closed-loop system represented in the given figure is a type -1 system.

Reason (R): Number of poles at the origin possessed by the feedback path decides the type of the closed-loop system a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): Data acquisition systems are widely used in a variety industrial and scientific areas. Reason (R): Data acquisition systems often use magnetic tape recorders. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): In fivre optic communication, the 1,3  m , window is

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preferred over the 0.85  m window for long distance communication. Reason (R): At 1.3  m not only the attenuation of silica fiber is lower than that at 0.85  m , the pulse broadening at the long wavelength window is also minimum. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): For transmitting audio frequency signals, antennas of several hundred kilometers length would be required. Reason (R): For efficient radiation of electromagnetic energy to occur from an antenna, the wavelength of the radiated signal must be comparable with the physical dimensions of the antenna. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): In a high frequency transmission line, when a voltage is placed across the line at the sending end, the voltage and current in the line change with distance. Reason (R): A transmission line consists of continuous conductors with a crosssectional configuration that is content throughout their lengths. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): MOSFET RAMs are usually slower than bipolar RAMs. Reason (R): MOSFET RAMs in comparison with bipolar RAMs can be fabricated in much larger capacity in a single IC and consume much less power. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true

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11 of 14 Assertion (A): A BJT amplifier needs very good bias stabilization circuit as compared to that of an FET amplifier circuit. Reason (R): The input p-n junction of FET amplifier is reverse biased and that of the BJT amplifiers forward biased. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): A monostable multivibrator can be used as a counter. Reason (R): The pulse width of the monostable multivibrator is a function of its input dc voltage. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): For a periodic inpu8t voltage whose amplitude is large enough to pass through the trip points, a Schmitt trigger produces a rectangular wave-form at the output. Reason (R): A Schmitt trigger is a comparator with positive feedback and hence prevents noise triggering. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): The multistage intermediate frequency amplifier of superheteroyne radio receiver is always staggered tuned. Reason (R): A very sharp tuned high gain amplifier is obtained maximizing the gain and increasing the fidelity of the receiver. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): Three-phase transformers of different vector groups should not be operated in parallel.

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Reason (R): Transformers belonging to different vector groups will not have the same phase sequence on the secondary side. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true Assertion (A): In a 3-phase induction motor, the stator is to be wound for 4 poles but by mistake, the rotor is wound for 2 poles only. When the stator is fed from a 50Hz, 3-phase supply with rotor winding shorted, the motor does not start up. When however, the wound rotor is replaced by a squirrel-cage rotor, the machine operates without any problem. Reason (R): Rotor of an induction motor should not have any poles. a. Both A and R are true and R is the correct explanation of A b. Both A and R are true but R is not a correct explanation c. A is true bur R is false d. A is false but R is true The current I1 through the 5  resistor in the network shown in the figure, is

a. 8.58 A b. 7.54 A c. 11.66 A d. 14 A. A lamp rated at 10watts, 50 volts is proposed to be used in 110 volts, system. The wattage and resistance of the resistor to be connected in series with lamp should be a. 15 watts, 350 ohms b. 1o watts, 250 ohms c. 12 watts, 300ohms d. 15 watts, 250 ohms Match List I with List II and select the correct answer using the codes given below: List I A. Superaposition theorem B. Thevenin theorem

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12 of 14 C. Signal flow graph D. Complex frequency List II 1. Current source 2. linearity 3. s-plane 4. mason’s gain formula 5. Voltage source A B C D a. 2 1 4 5 1 2 4 5 b. c. 2 5 3 4 2 5 4 3 d. Thevenin’s equivalent resistance Rth for the network shown in the given figure is known to be 2  . The value of R in ohms is

a. 1 b. 2 c. 3 d. 4 The driving-point impedance of the network shown in the figure is given by

a. b. c. d.

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4  s  3 / 2  s  5 / 4

 s  3 / 2  s  5 / 4  s  5 / 4  s  3 / 2 1  s  3 / 2 4  s  3 / 2

The correct value of the current I (t) at any instant when K is switched on at t = 0 in the network in the given figure is

E E  R / L t  e R R E E  e  R / L t b. R R E E   R / L t c.  e R R E E   R / L t d.  e R R For the given tow-port network, Z21 will be a.

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a. 2/5  b. 3/5  c. 1/5  d. 4/5  If the driving-point admittance function of Ks , it can be a 1-port network is Y  s   s  realized using a. Series combination R,L b. Parallel combination of R,L c. Series combination of R,C d. Parallel combination of R,C

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The pole-zero plot of a network function H(s) is shown in the given figure. Which one of the following will be the correct nature of its frequency response plots?

a. The amplitude plot will decay with frequency but the phase plot will be constant at all frequencies b. The amplitude plot will be constant but the phase plot will vary from +180° to

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13 of 14 +90° as frequency varies from zero to infinity c. The amplitude and phase plots will be consent at all frequencies d. The amplitude plot will be constant but the phase plot will vary form +180° to 0° s the frequency varies from zero to infinity In a series resonant circuit, which one of the following will increase on increasing the inductance to four times its value and reducing the capacitance to one-fourth of its value? a. Resonant frequency b. Current at resonant frequency c. Impedance at resonant frequency d. Selectivity of the circuit A series RLC circuit draws current at leading power factor at a. The resonant frequency b. Frequency less than the resonant frequency c. Frequencies more than the resonant frequency d. Frequencies both less and more than the resonant frequency One of the two wattmeter has read zero in the two-wattmeter method of power measurement. This indicated that the load phase angle is a. 0° b. 30° c. 60° d. 90° In the circuit shown in the given figure, three-phase supply is connected to a starconnected load. If ammeters A1, A2, A3 read 12.5 A, what will be the reading of ammeter AN?

a. 37.5A 37.5 A b. 3 c. 37.5 3A d. Zero For the circuit shown in the given figure, if R = 10  , XL=0.1  and Xc=0.1  , then the fur rent through R is

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a. 0 b. 10I c. I d. 0.11 Two coupled coils have L1 = 0.6 H, L2=0.6H and coupling coefficient = 0.25. coil 2 has 800 turns. If current I1 in coil is 6sin 100t amps, then the voltage across coil 2 is a. 90cos 100t volts b. 9cos 100t volts c. 0.9cos 100t volts d. 0.09cos 100t volts If a charge of one coulomb is to be brought to a distance of one meter from a charge of 2 coulomb, then the work required is 1 a. N m 2 0 1 N m b. 4 0 c. 2 0 N  m d. 4 0 N  m A small permanent magnet makes small oscillations in a uniform magnetic field as shown in the given figure. The period of oscillations is T. if the strength of the magnetic field is doubled, the period of oscillations will be

a. 2T b. T 2 c. T / 2 d. T/2 A uniform plane electromagnetic wave with electric component E = Em cos t  px  propagates in vacuum along the positive x-direction. The mean pointing vector is given by 1 a.  0 c 2 Em2 /  2 1 b. 0 c 2 Em2 /  2

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14 of 14 1 0 cEm /  c. 2 1 d.  0 c 2 Em /  2 Match List I (Antemma) with List II (Application/Characteristics) and select the correct answer using the codes given below the lists: List I A. A quarter wave monopole over ground plane B. A vertical half-wave dipole C. Folded dipole D. Hertzian dipole (length<  100) List II 1. radiation resistance 1 >1