INDIAN SPACE RESEARCH ORGANISATION. Recruitment Entrance Test for Scientist/Engineer SC 2017

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1 1. n inductance of one H carrying a current of two amperes will store the energy of watts joules 4 watts 4 joules. The square waveform of current has following relation between r.m.s value and average value r.m.s. value of current is greater than the average value r.m.s. value of current is less than the average value r.m.s. value of current is equal to the average value There is no definite relation between the r.m.s. value and average value for a square wave 3. Two numbers of 500 ohms one watt resistors are connected in parallel. Their combined resistance and wattage rating will be 50 ohms, 1 watt 50 ohms, watts 1000 ohms, watts 500 ohms, watts 4. In a long uniform coil of inductance L and associated resistance R ohms is physically cut in to two exact halves which are rewound in parallel. The resistance and inductance of the combination are R and L R and L R/ and L/ R/4 and L/4 5. For transfer function of a physical two-port network ll zeros must lie only in the left half of the s-plane ll poles may lie anywhere in the s-plane The poles lying on the imaginary axis must be simple ll the above Electrical 3

2 6. The starting torque of a three phase induction motor can be increased by Increasing rotor reactance Increasing rotor resistance Increasing stator resistance None of the above 7. The capacitor start-capacitor run single phase induction motor is operationally a Single phase motor Two phase motor Three phase motor.c. series motor 8. What would happen if the field of a D.C. shunt motor is opened? Speed will be reduced Continue to run normally Speed will enormously increase damaging the motor None of the above 9. Equalizer rings in D.C. generator with lap windings are used for Equal distribution of current at brush for sparkless commutation Prevention of harmonics Reduction of noise and vibration voiding overhang 10. The Buchholz relay is normally used to protect the lternators against all internal faults Oil immersed transformers against all internal faults Synchronous motors against all internal faults Transmission lines against all short circuit faults 11. The power transformer is a Electrical 4

3 Constant current device Constant voltage device Constant power device Pulsating main flux device 1. change of 5% in supply voltage to an induction motor will produce a change of approximately 5% in the rotor torque 7.5% in the rotor torque 10% in the rotor torque 5% in the rotor torque 13. If the supply frequency to the transformer is increased, the iron loss Will increase Will decrease Will not change May reach zero 14. The maximum temperature permitted for class insulation is 180 degree centigrade 105 degree centigrade 10 degree centigrade None of the above 15. Two transformers connected in parallel share load in the ratio of their KV ratings, provided their ohmic impedance are Equal In direct ratio of their ratings In inverse ratio of their ratings Purely reactive 16. The high frequency hum in the transformers is mainly due to Loose laminations Magnetostriction Impurity in oil Weakness of tank wall /00 volts transformer has pu impedance of The HV side voltage required to circulate full load current during short circuit test is Electrical 5

4 0 V 40 V 10 V 5 V 18. Non-loading heat run test on transformers is performed by means of SC test OC test Core balance test Sumpner s test 19. three phase induction motor is driving full-load torque which is independent of speed. If the line voltage drops to 90% of the rated value, % increase in motor copper losses 3% 18% 13% None of these 0. synchronous generator is feeding power to infinite bus bars at unity power factor. Its excitation is now increased. It will feed The same power but at a leading power factor The same power but at a lagging power factor More power at unity power factor Less power at unity power factor 1. The steam input in to a turbogenerator connected to infinite bus is increased. Which of the events will take place? The generator will feed more leading KVR to bus bar and power angle will not change The generator will feed more real power to bus bar and power angle will increase The generator will feed more power to bus bar and power angle will decrease The generator will feed more lagging KVR to bus bar and power angle will not change. In an ideal transformer, which of the following statement is correct? no voltage drops in resistance or leakage reactance Electrical 6

5 mmf required to maintain main flux is small no core loss all the above are correct 3. The voltage applied to a transformer primary is increased keeping v/f fixed. How will core loss and magnetizing current change? Core loss will increase and magnetizing current remain same Core loss will remain same and magnetizing current will remain same Core loss will decrease and magnetizing current will increase Core loss will remain same and magnetizing current will decrease 4. Frequencies in the UHF range normally propagate by means of Ground waves Sky waves Surface waves Space waves 5. Indicate the antenna that is not wideband Discone Folded dipole Helical Marconi 6. The depth of penetration of a wave in a lossy dielectric increases with increasing Conductivity Permeability Wavelength Permittivity 7. Copper behaves as a Conductor always Conductor or dielectric depending on field strength Electrical 7

6 Conductor or dielectric depending on frequency Conductor or dielectric depending on the electric current density 8. ssuming constant transmission efficiency, if voltage is increased n times, the size of the conductor would be Reduced to Increased to 1 n that of the original n that of the original Reduced to 1 n that of the original Increased to n times that of the original 9. Shunt conductance in overhead power transmission lines is primarily due to Leakage over the insulators Leakage over the conductors Leakage over the poles Leakage between ground and conductors 30. The dielectric strength of SF6 gas (used in circuit breakers) is approximately Same as that of air to 3 times more than air 10 to 0 times more than air to 3 times less than air 31. Ferranti effect states that under certain conditions, the sending end voltage is Less than receiving end voltage Greater than receiving end voltage Equal to receiving end voltage Not having any impact on the receiving end voltage 3. The equal area criterion of stability is applicable to Two machine system and infinite bus bars One machine system and infinite bus bars Electrical 8

7 Multi-machine system only None of the above 33. The power transmission capacity of the transmission line is Inversely proportional to the square of the voltage Proportional to the voltage Inversely proportional to the voltage Proportional to the square of the operating voltage 34. If the torque angle delta increases indefinitely, the system indicates Steady state stability Permanent stability Instability None of the above 35. Resistance switching is normally employed in ll breakers Bulk oil breaker Minimum oil breaker ir-blast circuit breaker 36. Series capacitors are used to Improve line frequency and eliminate harmonics Compensate for line inductive reactance Neutralise line capacitive reactance None of the above 37. Over fluxing protection is normally recommended for Generator transformers in power stations uto-transformers in power stations Station transformers in power stations Electrical 9

8 Distribution transformers 38. In general C distribution systems, arc interruption in vacuum circuit breakers are designed to function in a time period of One cycle Two to three cycles Within ten cycles None of the above 39. Systems for Protection from negative sequence current is provided normally for Transformers Generators Transmission lines Motors 40. Bundled conductors are mainly used in high voltage overhead transmission lines to Reduce line loss Reduce harmonics Reduce corona Increase strength 41. Surge impedance of overhead transmission line is normally in the order of 1 5 ohms 0 30 ohms ohms ohms 4. The bode diagram approach is applied to Non-minimum phase network Minimum phase network ny network of a control system None of the above 43. Which of the following methods is the strongest tool to determine the stability and the transient response of the system? Routh-Hurwitz criterion Bode plot Nyquist plot Root locus Electrical 10

9 44. If the gain of a critically damped system is increased, it will become Under damped system Over damped system Oscillatory system Critically damped system 45. The frequency domain and time domain are related through Laplace transform Gauss elimination Both and None of the above system with characteristic equation s + s + 11 s + 18s + 18 = 0 will have closed loop poles such that ll poles lie in the left half of the s-plane ll poles lie in the right half of the s-plane Two poles lie symmetrically on the imaginary axis of the s-plane. No pole lies on the imaginary axis of the s-plane. 47. If the gain of an open loop system is doubled, the gain margin Is not affected Gets double Becomes half Becomes one-fourth 48. n all pass network imparts only Negative phase to the input Positive phase to the input +/ 90 degree phase shift to the input +/ 180 degree phase shift to the input 49. n ON-OFF controller is P controller Integral controller Non-linear controller PID controller Electrical 11

10 50. The transfer function of a phase lead controller is (1 + 3Ts) / (1 + Ts). The maximum value of phase provided by this controller is The thermal time constant is the time To reach the final steady temperature if the initial rate of increase of temperature were maintained constant To reach 63% of final steady temperature To reach 66.66% of final steady temperature To reach half of the final steady temperature 5. Which of the following circuit will have no transients? Pure resistive circuit L-C Circuit R-L-C Circuit R-L Circuit 53. conductor of length 100 cm moves right angles to a magnetic field of flux density of wb/sq.m. with the velocity of 5 m/second. The induced emf in the conductor will be 5 volts 50 volts 75 volts 100 volts 54. Which of the following devices are required to measure three phase balanced power? One watt meter One watt meter and one voltage transformer of 1 : 1 ratio One watt meter and two voltmeters None of the above Electrical 1

11 55. The sensitivity of an instrument is The smallest increment in the input that can be detected with certainty The largest input change to which the instrument fails to respond Ratio of the change in the magnitude of the output to the corresponding change in the magnitude of the input Closeness of the output values for repeated application of a constant input 56. Potentiometer sensitivity can be increased by Decreasing current in the potentiometer wire Increasing the length of the potentiometer wire Decreasing the length of the potentiometer wire Replacing the cell by a regulated power supply 57. Low resistance is measured with De Sauty s bridge Maxwell s bridge Kelvin s double bridge Wien bridge 58. Which bridge is used to determine frequency? nderson bridge De Sautys bridge Wien bridge Campell s bridge 59. The core of a moving iron instrument is made up of permalloy to Increase sensitivity Reduce temperature effect Reduce effect of stray magnetic field Reduce the size of the instrument Electrical 13

12 60. ccuracy is defined as The measure of consistency of the readings Closeness with which an instrument reading approaches the true value of the quantity being measured The smallest measurable input change The ratio of the input to output 61. If three amplifiers having the same bandwidth are cascaded, the bandwidth of the resulting amplifier will be Better than that of each stage Worse than that of each stage Same as that of each stage None of the above 6. n element is said to have negative resistance when The element has negative temperature coefficient The current / voltage curve has negative slope The element has negative specific resistance The current / voltage curve has a positive slope 63. The operational amplifiers are seldom used for differentiation because Of the problem of drift with differentiating circuits Because of the poor efficiency Because of the complex circuitry requirements The noises are amplified and this can be significant in the output. 64. Which of the following multivibrator is called the flip flop? Electrical 14

13 stable multivibrator Monostable multivibrator Bistable multivibrator Both and 65. The amount of feedback applied to an amplifier reduces the gain by a factor of 10. The bandwidth Decreases by factor of 10 Increases by a factor of 10 Remains the same None of the above 66. In a negative feedback amplifier, the output impedance is decreased If the signal sampled is a voltage If the signal sampled is a current If the feedback signal is a voltage If the feedback signal is a current 67. The ROM consists of decoder followed by an encoder n encoder followed by a decoder multiplexer followed by a decoder multivibrator 68. n ideal rectifier should have transformer utilization factor (TUF) of 1. If the actual TUF is 3.5, it shows that Diode is under-loaded The transformer must be 3.5 times larger The transformer should be only 1/3.5 times the ideal size The ripple factor is low 69. power MOSFET is a Electrical 15

14 Voltage controlled device Current controlled device Frequency controlled device None of the above 70. When transistors are used in series or parallel, a snubber circuit is used to Control the current Control the voltage Limit di dt ll of these 71. x + sin x lim equals to x x fair (unbiased) coin was tossed four times in succession and resulted in the following outcomes: (i) Head (ii) Head (iii) Head (iv) Head. The probability of getting a Tail when the coin is tossed again is 0 1/ 4/5 1/5 73. What are the eigen values of the following matrix 1 and 1 1 and 6 and 5 4 and ? π π sin ( x y) 0 0 dx dy is Electrical 16

15 0 π π 75. In the Taylor series expansion of e x + sin x about the point x = π, the coefficient π e 0.5 π e π +1 e π 1 e 76. deck of five cards (each carrying a distinct number from 1 to 5) is shuffled thoroughly. Two cards are then removed from the deck, one at a time. What is the probability that the two cards are selected with the number of the first card being one higher than the number on the second card? Using trapezoidal rule for the table given below ln x dx will be 4 x : Ln x : Find the z transform of ( n +1) Electrical 17

16 z ( z + 1) ( z 1) 3 ( z + 1) ( z 1) 3 + z ( z 1) ( 3z + ) z Consider the following system of equations in three real variables x1, x and x 3 x x 1 3x 1 x 1 x 4x + 3x 3 + 5x + x = = = 3 The system of equations has : No solutions unique solution More than one but a finite number of solutions n infinite number of solutions 80. Which of the following functions would have only odd powers of x in its Taylor series expansion about the point x = 0? 3 sin ( x ) sin ( x ) 3 cos ( x ) cos ( x ) Electrical 18

17 Space for rough work Electrical 19

18 Space for rough work Electrical 0

ENGINEERING ACADEMY X V

ENGINEERING ACADEMY X V 1. Two incandescent bulbs of rating 230, 100 W and 230, 500 W are connected in parallel across the mains. As a result, what will happen? a) 100 W bulb will glow brighter b) 500 W bulb will glow brighter