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BSNL JTO 2001 - Previous Paper with Solutions

1. Function corresponding to the Bode plot of the Figure below is
Answer: D

2. A fixed capacitor of reactance –j0.02 ohm is connected in parallel across a series combination of a fixed inductor of reactance j0.01 ohm and a variable resistance R. As resistance R is varied from zero to infinity, the locus diagram of the admittance of this L-C-R circuit will be
(a) A semi-circle of diameter j 100 and center at zero
(b) A semi circle of diameter j50 and center at zero
(c) A straight line inclined at an angle
(d) A straight line parallel to the x-axis
Answer: A

3. The voltage phasor of a circuit is 10∟15º V and the current phasor is 2∟-45º A. The active and the reactive powers in the circuit respectively are.
(a) 10W and 17.32 VAR
(b) 5W and 8.66 VAR
(c) 20W and 60 VAR
(d) 2002 W and 1002 VAR
Answer: A

4. A current of [2√2 sin(314t + 30) + 2√2 cos(952t + 45)] is measured with a thermocouple type 5 Amp full scale, class I meter. The meter reading would lie in the range
a. 5A ± 1%
b. (2 + 3√2)A ± 1%
c. 3A ± 1.7%
d. 2A ± 2.5%
Answer: C

5. A dual-slope analog-to digital converter uses an N-bit counter. When the input signal Va is being integrated, the counter is allowed to count up to a value
(a) equal to 2N – 2
(b) equal to 2N – 1
(c) proportional to Va
(d) inversely proportional to Va
Answer: D

6. A step down chopper operate from a dc voltage source Vs, and feeds a dc motor armature with a back emf Eb. From oscilloscope traces, it is found that the current increases for time tr, falls to zero over time tf, and remains zero for time t0, in every chopping cycle. Then the average dc
voltage across the freewheeling diode is
Answer: C

7. The characteristic equal of a feedback control system is
2s4 + s3 + 3s2 + 5s + 10 = 0
The number of roots in the right half of s-plane are
(a) 0
(b) 1
(c) 2
(d) 3
Answer: C

8. Maximum phase-lead of the compensator D(s) = (0.5s + 1) / (0.05s + 1)
(a) 52 deg at 4 rad/sec
(b) 52 deg at 10 rad/sec
(c) 55 deg at 12 rad/sec
(d) None of these
Answer: D

9. An 8 bit successive approximation analog to digital converter has a full scale reading of 2.55V and its conversion time for an analog input of 1V is 20ms. The conversion time for a 2V input will be
(a) 10ms
(b) 20ms
(c) 40ms
(d) 50ms
Answer: B

10. The amplitude modulated waveform S(t) = Ac[1 + Kam(t)] cosωct is fed to an ideal envelop detector. The maximum magnitude of Kam(t) is greater than 1. Which of the following could be the detector output?
Answer: C

11. In free space, the time averaged poynting vector in W/m2, for the wave given below is
Answer: A

12. Figure shown below is a mod – K counter. The value of K is
a. 1
b. 2
c. 3
d. 4
Answer: D

13. In the MOSFET amplifier of the figure shown, the signal outputs V1 and V2 obey the relationship
Answer: D

14. In a JK flip-flop, we have K = 1. Assuming the flip-flop was initially cleared and then clocked for 6 pulses, the sequence at the output Q will be
a. 010000
b. 011001
c. 010010
d. 010101
Answer: D
15. The decoding circuit shown in the figure below used to generate the actve low select signal for a microprocessor peripheral. (The address lines are designated as A0 to A7) for IO addresses. The peripheral will correspond to IO address in the range
Answer: A

16. A deterministic signal has the power spectrum given in the figure below.
The minimum sampling rate needed to completely represent this signal is
a. 1KHz
b. 2 KHz
c. 3 KHz
d. None
Answer: C

17. A rectangular air-filled waveguide has cross section of 4 cm X 10 cm. The minimum frequency which can propagate in the waveguide is
a. 1.5 GHz
b. 2.0 GHz
c. 2.5 GHz
d. 3.0 GHz
Answer: A

18. A 1 km long microwave link uses two antennas each having 30 dB gain. If the power transmitted by one antenna is 1 W at 3 GHz, then the power received by the other antenna is approximately
a. 96 µW
b. 76.8 µW
c. 63.4 µW
d. 55.2 µW
Answer: C

19. The following sequence of instruction are executed by an 8085 microprocessor
1000 LXI SP, 27FF
1003 CALL 1006
1006 POP H
The contents of the stack pointer (SP) and the HL register pair on completion of execution of these are
a SP = 27FF, HL = 1003
b. SP = 27FD, HL =1003
c. SP = 27FF, HL =1006
d. SP = 27FD, HL =1006

20. Value of R in the oscillator circuit shown in the figure shown below, is chosen such that the circuit oscillates at an angular frequency of ω.
The value of ω and the required value of R will be respectively
a. 105 rad/sec, 2 x 104
b. 2 x 104 rad/sec, 2 x 104
c. 2 x 104 rad/sec, 105
d. 105 rad/sec, 105
Answer: A

21. A silicon n-MOSFET has a threshold voltage of 1 volt and oxide thickness of 400 Ao. The region under the gate is ion implanted for threshold voltage tailoring. The dose and type of the implant (assumed to be a sheet charge at the interface) required to shift the threshold voltage to – 1 volt are
a. 1.08 x 1012 /cm2, p-type
b. 1.08 x 1012 /cm2, n-type
c. 5.4 x 1011 /cm2, p-type
d. 5.4 x 1011 /cm2, n-type
Answer: A

22. A uniform plane wave in air is normally incident on an infinitely thick slab. If the refractive index of the glass slab is 1.5 then the percentage of the incident power that is reflected from the air-glass interface is
a. 0%
b. 4%
c. 20%
d. 100%
Answer: B

23. A 12 bit ADC is operating with a 1 µsec clock period and the total conversion time is seen to be 14 µsec. The ADC must be of the
a. Flash type
b. Counting type
c. Integrating type
d. Successive Approximation type
Answer: D

24. The output of the circuit shown the figure below is equal to
Answer: A

25. The diffusion potential across a PN junction
a. decreases with increasing doping concentration
b. increases with decreasing band gap
c. does not depend on doping concentration
d. increases with increase in doping concentration
Answer: D

26. The drift velocity of electrons in silicon
a. is proportional to the electric field for all values of electric field
b. Is independent of the electric field
c. Increases at low values of electric field and decreases at high values of electric field exhibiting negative differential resistance
d. Increase linearly with electric field at low values of electric field and gradually saturates at higher values of electric field
Answer: D

27. V(t) = 55[cos(106ωt – sin(103ωt) x sin(106ωt))] represents
(a) DSB suppressed carrier signal
(b) AM signal
(c) SSB upper sideband signal
(d) Narrow band FM signal
Answer: D

28. A small concentration of minority carries is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V / cm is applied across the crystal and this moves the minority carries a distance of 1 cm is 20  sec. The mobility (in cm2/volt. sec)
a. 1000
b. 2000
c. 5000
d. 500000
Answer: C

29. The 3-dB bandwidth of a typical second-order system with the transfer function given below is
Answer: C

30. In the given circuit, C0 is the distributed capacitance of the coil and C is the tuning capacitor. If C = C1 for the fundamental frequency and C = C2 for the second harmonic, then the value of C0 can be expressed as
Answer: B

31. A digital phase meter is shown in the figure below. If the input signals are VR (t) = VR sinwt and
VP(t) = VP sin (wt +30º), the reading of the meter will be
a. 30o
b. 330o
c. 150o
d. 210o
Answer: D

32. In the transistor circuit shown in the figure below, collector-to-ground voltage is +20V. Which of the following is the probable cause of error?
(a) Collector-emitter terminals shorted
(b) Emitter to ground connection open
(c) 10 k ohm resistor open
(d) Collector-base terminals shorted
Answer: B

33. A Lissajous pattern, as shown in the figure below, is observed on the screen of a CRO when voltages of frequencies fx and fy are applied to the x and y plates respectively. fx : fy is then equal to
a. 3:2
b. 1:2
c. 2:3
d. 2:1
Answer: D

34. In a multicavity magnetron, strapping is employed primarily
(a) To prevent mode jumping
(b) To increase the separation between the resonant frequencies in the π-mode and in the adjacent modes
(c) To reduce the back heating of the cathode
(d) To increase the output of the magnetron
Answer: A,B

35. The logic realized by the circuit shown in the figure is
Answer: B

36. Figure below shows the circuit of a gate in the Resistor Transistor Logic (RTL) family.
The circuit represents
b. AND
c. NOR
d. OR
Answer: D

37. The initial contents of the 4-bit serial-in-parallel out, right-shift, Shift Register shown in, Figure is
After three clock pulses are applied, the contents of the Shift Register will be
a. 0000
b. 0101
c. 1010
d. 1111
Answer: C

38. A silicon sample is uniformly doped with 1016 phosphorus atoms/cm3 and 2x1016 boron atoms/cm3. If all the dopants are full ionized, the material is
(a) n-type with carrier concentration of 1016/cm3
(b) p-type with carrier concentration of 1016/cm3
(c) p-type with carrier concentration of 2x1016/cm3
(d) n-type with carrier concentration of 2x1016/cm3
Answer: B

39. The open loop transfer function of a feedback control system is G(s)H(s) = 1 / (S + 1)3. The gain margin of the system is
a. 2
b. 4
c. 8
d. 16
Answer: C

40. A second order system has a transfer function given by G(s) = 25 / (8s2 + 8s +25). If the system initially at rest is subjected to a unit step input at t=0, the second peak in the response will occur at
a. π sec
b. π/3 sec
c. 2π/3 sec
d. π/2 sec
Answer: A

41. Two isotropic antennas are separated by a distance of two wavelengths. If both the antennas are fed with currents of equal phase and magnitude, the number of lobes in the radiation pattern in the horizontal plane are
a. 2
b. 4
c. 6
d. 8
Answer: B

42. Which of the following field equations indicate that the magnetic charges do not exist?
Answer: C

43. A 4 GHz carrier is DSB SC modulated by a low pass message signal with maximum frequency of
2MHz. The resultant signal is to be ideally sampled. The minimum frequency of the sampling in train should be
a. 4 MHz
b. 8 MHz
c. 8 GHz
d. 8.004 GHz
Answer: D

44. Zero mean white noise is passed through an ideal low pass filter with cut off at W Hz. The filter output will be uncorrelated at time instants spaced
Answer: B

45. LEDs have response time of the order of
a. 0.1 ns
b. 1 ns
c. 100 ns
d. 1 µs
Answer: C

46. In a uniformly doped abrupt p-n junction, the doping level of the n-side is four times the doping level of the p-side. The ratio of the depletion layer width is
a. 0.25
b. 0.5
c. 1.0
d. 2.0
Answer: A

47. An electromechanical closed-loop control system has the following characteristic equation
S3 + 6KS2 + (K + 2)S + 8 = 0, Where K is the forward gain of the system. The condition for closed loop stability is
a. K = 0.528
b. K = 2
c. K = 0
d. K = - 2.528
Answer: A

48. The impulse response and the excitation function of a linear time invariant causal systems are shown in Figures (a) and (b) respectively.
The output of the system at t = 2 sec is equal to
a. 0
b. 0.5
c. 3/2
d. 2
Answer: B

49. The open circuit impedance matrix of the 2-port network shown in the figure is
Answer: A

50. The response of an initially relaxed linear constant parameter network to a unit impulse applied at t = 0 is 4e-2t u(t ). The response of this network to a unit step function will be
Answer: B

51. In a twin-wire transmission line in air, the adjacent voltage maxima are at 12.5 cm and 27.5 cm.
The operating frequency is
a. 300 MHz
b. 1 GHz
c. 2 GHz
d. 6.28 GHz
Answer: B

52. Assume that the op-amp of the given Figure is ideal. If 2[1 - e2t]u(t) is a triangular wave, then v0
will be
a. Square wave
b. Triangular wave
c. Parabolic wave
d. Sine wave
Answer: A

53. A 75 ohm transmission line is first short terminated and the minima locations are noted. When the short is replaced by a resistive load RL, the minima locations are not altered and VSWR is measured to be 3. What is the value of RL?
a. 25 Ohm
b. 50 Ohm
c. 225 Ohm
d. 250 Ohm
Answer: C

54. On a resistively terminated high frequency lossless transmission line fed by a 500 MHz source, the VSWR is found to be equal to 2 and the first voltage minimum is measured at 30 cm from the load end. What is the value of the “normalized” load resistance?
a. 3
b. 2
c. 0.5
d. 0.25
Answer: B

55. The slow-wave structure of a TWT is provided with an attenuator. Which one of the following is the function of such an attenuator ?
(a) It prevents of RF power from reaching the output of the device when the beam is switched on
(b) It prevents oscillations in the device
(c) It reduces the noise level of the device
(d) It is used to broadband the device
Answer: C

56. Which one of the following is a transferred electron device?
(a) BARITT diode
(b) IMPATT diode
(c) Gunn diode
(d) Step recovery diode
Answer: C

57. The capacity of an analog communication channel with 4 kHz bandwidth and 15 dB SNR is approximately
(a) 20,000 bps
(b) 16,000 bps
(c) 10,000 bps
(d) 8,000 bps
Answer: A

58. The input pulses to the different stage of the counter shown in the following figure must be of
(a) Constant frequency and constant width
(b) Constant frequency but variable width
(c) Variable frequency but constant width
(d) Variable frequency as well as variable width
Answer: D

59. The circuit shown in the given figure is a
(a) Monostable multivibrator
(b) Frequency division circuit
(c) Miller sweep circuit
(d) Bootstrap sweep circuit
Answer: A

60. Measurement of Hall coefficient in a semiconductor provides information on the
(a) Sign and mass of charge carries
(b) Mass and concentration of charge carriers
(c) Sign of charge carriers alone
(d) Sign and concentration of charge carriers
Answer: B

61. According to a classical free electron theory, the relaxation time and mean free path for aluminium are respectively 0.75x10–14 s and 0.88 mm. Given that the density of aluminium is 2700 kg/m3 and the atomic weight of aluminium is 26.98, the resistivity of aluminium is
a. 1.73 x 10-8 Ω-m
b. 1.47 x 10-8 Ω-m
c. 2.62 x 10-8 Ω-m
d. 4.32 x 10-8 Ω-m
Answer: A

62. In the graph shown in the Figure, for the tree with branches b, d and f, the fundamental loops would include
1, 2, 3, 4 are nodes
a, b, c, d, e f are branches
(a) abc, def, bdea
(b) cea, bdea, abc
(c) cdb, def, bfa
(d) adbe, def, cdb
Answer: C

63. In cavity magnetron, strapping is used to
(a) Prevent mode jumping
(b) Prevent cathode back hearting
(c) Ensure bunching
(d) Improve the phase focusing effect
Answer: A

64. An antenna of input resistance 73 ohm is connected to a 50-ohm line. If losses are ignored, then its efficiency will be nearly
(a) 0.19
(b) 0.81
(c) 0.97
(d) 1.19
Answer: B

65. A, B and C are three parallel plates condensers with similar surface area of plates and similar separation. A contains air is dielectric, B contains glass as dielectric and C contains Polythene. If the electric field intensities in air, glass and polythene are respectively E1, E2 and E3 then (assume that the plates are filled with the given dielectrics)
a. E1 = E2 = E3
b. E1 = E2 > E3
c. E1 > E2 > E3
d. E1 < E2 > E3
Answer: C

66. The circuit diagram of an op-amp based amplifier is shown in the given figure.
The ratio Vout/Vin is equal to
a. 9
b. 11
c. 10
d. 21
Answer: B

67. The given figure shows a reflectometer arrangement to measure the parameters of an over coupled one port cavity resonator of f0. With 100 mW of input power, the output power at B is 6.4 mW. What is the value of the coupling coefficient represent?
a. 9
b. 6.4
c. 5
d. 2.5
Answer: B

68. A TE10 rectangular waveguide is to be designed for operation over 25-35 GHz and the band center is 1.5 times the cutoff frequency. What should be the dimension of the broad side?
(a) 15 mm
(b) 10 mm
(c) 9 mm
(d) 7.5 mm
Answer: D

69. In π-mode operation of magnetron, the spokes due to phase focusing effect rotate at an angular velocity corresponding to
(a) One poly/cycle
(b) Two poly/cycle
(c) Four poles/cycle
(d) Six poly/cycle
Answer: D

70. What is the slope change at ω = 10 of the magnitude v/s frequency characteristic of a unity feedback system with the following open-loop transfer function?
Answer: D

71. An amplifier operating over the frequency range of 18 to 20 MHz has a 10kW input resistance.
The RMS noise voltage at the input to the amplifier at ambient temperature of 27oC is (Assume the Boltzman constant value as 1.38x10–23 J/K)
a. 18.2 µV
b. 17.2 µV
c. 16.2 µV
d. 14.2 µV
Answer: A

72. In the root locus for open loop transfer function, G(s) = K(s+6) / (s+3)(s+5) , the break away and break in points are located respectively at
a. – 2 and – 1
b. – 2.47 and – 3.77
c. – 4.27 and – 7.73
d. – 7.73 and – 4.27
Answer: C

73. Under what condition will the instrumentation amplifier circuit given in the Figure possess highest CMRR? ( Rs1 and Rs2 are source resistances)
Answer: B

74. A square waveguide carries TE11 mode whose axial magnetic field is given by
where the waveguide dimensions are in centimeters. What is the cutoff frequency of the mode?
(a) 5 GHz
(b) 7.5 GHz
(c) 6.5 GHz
(d) 8 GHz
Answer: B

75. Noise temperature (T), and gain (G) are two important parameter of satellite antennas. Which one of the following antennas has the largest G/T ratio?
(a) Parabolic reflector
(b) Cassegranian antenna
(c) Pyramidal horn antenna
(d) Dipole antenna
Answer: B

76. The semiconductor diode which can be used in switching circuits at microwave range is
(a) PIN diode
(b) Varactor diode
(c) Tunnel diode
(d) Gunn diode
Answer: A

77. A conductor having surface density s is embedded in a dielectric medium of permittivity ε. The electric field in the medium is E. If it is known that the pressure p on the conductor surface is equal to the electric energy density in the medium, then p (in SI units) is given by
Answer: D

78. Which one of the following is the Fourier transform of the signal given in Figure (b) if the Fourier
transform of the signal in Figure (a) is given by
Answer: B

79. Microwave antenna aperture efficiency depends on
(a) Feed pattern
(b) Antenna aperture
(c) Surface losses
(d) Low side lobe level
Answer: B

80. A parabolic dish has a diameter of 10m. The maximum possible (ideal) gain of the antenna at λ = 3.14 cm will be
(a) 30 dB
(b) 40 dB
(c) 50 dB
(d) 60 dB
Answer: D

81. The demarcation between Fresnel region and Fraunhofer region fairly approximated by minimum distance between antennas for pattern measurement is (given that R = distance between antennas, D = largest aperture dimension and λ = wavelength)
a. R = λ/D2
b. R = λ2/2D2
c. R = 2D2
d. R = 2D22
Answer: C

82. A control system is as shown in the given Figure.
The maximum value of gain K for which the system is stable is
a. √3
b. 3
c. 4
d. 5
Answer: D

83. The logic circuit given below converts a binary code Y1Y2Y3 into
(a) Excess-3 code
(b) Gray code
(c) BCD code
(d) Hamming code
Answer: B

84. Which of the following oriented graphs have the same fundamental loop matrix?
Select the correct answer using the codes given below
(a) 1 and 2
(b) 2 and 3
(c) 1, 3 and 4
(d) 2, 3 and 4
Answer: B

85. The Q of a radio coil
(a) Is independent of frequency
(b) Increase monotonically as frequency increases
(c) Decreases monotonically as frequency increases
(d) Increases upto a certain frequency and then decreases beyond that frequency
Answer: D

86. The arrangement shown in the given figure represents an RC potentio meter for measuring and voltage. What should be the value of C so that Vo/Vin is independent of the frequency of the input signal?
a. 10 µF
b. 11 µF
c. 0.10 µF
d. 0.09 µF
Answer: A

87. In a rectangular cavity resonator having a = width, b = height and d = length. For a > b < d, the dominant mode is
a. TE101
b. TM101
c. TE110
d. TM110
Answer: A

88. Two isotropic antennas are separated by a distance of two wavelengths. If both the antennas are with currents of equal phase and magnitude, the number of lobes in the radiation pattern in the horizontal plane is
a. 2
b. 4
c. 6
d. 8
Answer: D

89. If the vector field
represents a magnetic field, then the value of k must be
a. 1
b. 2
c. – 1
d. – 2
Answer: D

90. An infinite number of concentric rings carry a charge Q each alternately positive and negative.
Their radii are 1, 2, 4, 8 ….. meters in geometric progression as shown. The potential at the center of the will be
Answer: D

91. Two concentric square loops A and B carry equal currents in the same direction. The magnetic field at O due to the two loops A and B will be in the ratio
a. 1:1.414
b. 1:1
c. 1.414:1
d. 2:1
Answer: D

92. In the circuit shown in the Figure below X in an element which always absorbs power. During a particular operation, it sets up a current of 1 amp in the direction shown and absorbs a power Px. It is possible that X can absorb the same Px for another current I, the value of this current is
Answer: D

93. A water boiler at home is switched on to a.c. mains supplying power at 230 V/50 Hz. The frequency of instantaneous power consumed by the boiler is
a. 0 Hz
b. 50 Hz
c. 100 Hz
d. 150 Hz
Answer: C

94. For the system shown in the figure below with a damping ratio ζ of 0.7 and an undamped natural
frequency ωn of 4 rad/sec, the values of K and a are
a. K = 4, a = 0.35
b. K = 8, a = 0.455
c. K = 16, a = 0.225
d. K = 64, a = 0.9
Answer: C

95. Gauss-Seidel iterative method can be used for solving set of
(a) Linear differential equations only
(b) Linear algebraic equations only
(c) Both linear and nonlinear algebraic equation
(d) Both linear and nonlinear differential equations
Answer: B

96. The phase lead compensation is used to
(a) Increase rise time and decrease overshoot
(b) Decrease both rise time and overshoot
(c) Increase both rise time and overshoot
(d) Decrease rise time and increase overshoot
Answer: D

97. Viewed from the terminals A, B the following circuit shown in the Figure below can be reduced to an equivalent circuit of a single voltage source in series with a single resistor with the following parameters
(a) 5 volt source in series with 10 Ω resistor
(b) 7 volt source in series with 2.4 Ω resistor
(c) 15 volt source in series with 2.4 Ω resistor
(d) 1 volt source in series with 10 Ω resistor
Answer: B

98. Figure below shows the input attenuator of a multimeter. The meter reads full scale with 12V at M, with the range switch at position ‘q’. What is the required voltage M to obtain full scale deflection with the range switch a position‘s’?
a. 1 volt
b. 150 volts
c. 120 volts
d. 147 volts
Answer: C

99. Figure below shows the electrostatic vertical deflection system of CRT. Given that VA is the accelerating voltage, the deflection sensitivity (deflection/volt) is proportional to
Answer: C

100. For a flip-flop formed from two NAND gates as shown in the figure below, the unusable state
corresponds to
a. X = 0, Y = 0
b. X = 0, Y = 1
c. X = 1, Y = 0
d. X = 1, Y = 1
Answer: A