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ISRO 2016 Electronics Question Paper with Answers

ISRO 2016 Electronics (Set - E)

1. How does the dynamic resistance of diode vary with temperature?
a. Directly proportional
b. Inversely proportional
c. Independent
d. Directly to the square of temperature
Answer: A

2. The electric field component of a time harmonic plane EM wave traveling in a non-magnetic lossless dielectric medium has amplitude of 2 V/m. If the relative permittivity of the medium is 4, the magnitude of the time average power density vector in W/m2 is
a. 1/30π
b. 1/120π
c. 1/60π
d. 1/240π
Answer: A



3. The force on a point charge +q kept at a distance ‘d’ from the surface of an infinite grounded metal plate in a medium of permittivity ε is
a. 0
b. q2/16πεd2 away from the plate
c. q2/16πεd2towards the plate
d. q2/4πεd2 towards the plate
Answer: C

4. A material has conductivity of 10-2 mho/m and a relative permittivity of 4. The frequency at which the conduction current in the medium is equal to the displacement current is
a. 45 MHz
b. 90 MHz
c. 450 MHz
d. 900 MHz
Answer: A

5. A system has fourteen poles and two zeros. Its high frequency asymptote in its magnitude plot having a slope of
a. – 40 dB/decade
b. – 240 dB/decade
c. – 280 dB/decade
d. – 320 dB/decade
Answer: B

6. A 1mW video signal having a bandwidth of 100 MHz is transmitted to a receiver through a cable that has 40 dB loss. If the effective one sided noise spectral density at the receiver is 10-20 Watt/Hz, then the signal to noise ratio at the receiver is
a. 50 dB
b. 30 dB
c. 40 dB
d. 60 dB
Answer: A

7. When the 8051 is reset and the line is HIGH, the program counter points to the first program instruction in the
a. Internal code memory
b. External code memory
c. Internal data memory
d. External data memory
Answer: A
 
8. How is the status of the carry, auxiliary carry and parity flag affected after executing instructions?
MOV A, #9CH
ADD A, #64H
a. CY = 0, AC = 0, P = 0
b. CY = 1, AC = 1, P = 0
c. CY = 0, AC = 1, P = 0
d. CY = 1, AC = 1, P = 1
Answer: B

9. In the given combinational logic, X is given by
Answer: A

10. Each transistor in Darlington pair (as shown in Fig) has hfe = 100. Overall hfe of composite transistor neglecting leakage current is,
a. 10000
b. 10001
c. 10100
d. 10200
Answer: C

11. In a given network shown in figure, a steady state is reached with switch ‘k’ open. At t=0, which is closed. Determine the values of I1, I2 and I3 at t = 0+ (in Amperes).
a. 1, 1/3, 0
b. 1/3, 1/3, 1/3
c. 0, 0, 0
d. 1, 1, 1
Answer: A

12. Simplify Boolean function represented in sum of products of min-terms, F(x,y,z) = ∑m(0,2,4,5,6)
Answer: A

13. A system is described by the transfer function H(s) = 1/(S3 + αS2 + kS + 3) is stable. The constraints on α and k are
a. α > 0, αk < 3
b. α > 0, αk > 3
c. α > 0, αk > 0
d. α > 0, αk < 0
Answer: B

14. Consider a unity feedback system whose open loop transfer function is G(s) = k/s(s2 + 2s +2). The Nyquist plot for this system is
Answer: B

15. Eye diagram gives an idea of
a. Modulation scheme
b. Clock jitter
c. SNR
d. All of the above
Answer: D

16. The signal flow diagram for a certain feedback control system is shown in figure.
Now consider the following set of equations for the nodes.
1. x2 = a1x1 + 19x3
2. x3 = a2x2 + a8x4
3. x4 = a3x3 + a5x2
4. x5 = a4x4 + a6x2
Which of the following are correct?
a. 1, 2 and 3
b. 1, 3 and 4
c. 2, 3 and 4
d. 1, 2 and 4
Answer: D

17. The appropriate output frequency of 555 oscillator for RA = RB = 2.2 kΩ and C = 2000 pF
a. 110 kHz
b. 109.3 kHz
c. 120.5 kHz
d. 108.9 kHz
Answer: B

18. A counter is designed using J-K flip flop as shown in figure.
Define its count sequence
a. 000, 001, 010, 011, 100 & repeats
b. 100, 011, 010, 001, 000 & repeats
c. 010, 011, 100, 000, 001 & repeats
d. 101, 110, 111, 000, 001, 010, 011, 100 & repeats
Answer: B

19. A 1 MHz clock signal is applied to a J-K flip flop with J=K=1. What is the frequency of the flip flop output signal?
a. 2 MHz
b. 500 kHz
c. 250 kHz
d. 500 MHz
Answer: B

20. How many inputs and outputs does a full adder have?
a. 3,2
b. 2,3
c. 3,3
d. 2,2
Answer: A

21. Which shift register counter requires the most decoding circuitry?
a. Jhonson counter
b. Ring counter
c. Ripple counter
d. MOD counter
Answer: A

22. A 10 bit DAC has step size of 10mV. What is its Full scale output voltage and the percentage resolution?
a. 10.24 V, 0.2 %
b. 10.23 V, 0.5 %
c. 10.23 V, 0.1 %
d. 10.24 V, 0.1 %
Answer: C

23. If the input signals A , B and output signals are shown as below,
then the circuit element is
a. AND gate
b. OR gate
c. NOR gate
d. XOR gate
Answer: C

24. For a 10 bit digital ramp ADC using 500 kHz clock, the maximum conversion time is
a. 2048 µs
b. 2064 µs
c. 2046 µs
d. 2084 µs
Answer: C

25. In digital filters, how many interpolated data points are inserted between samples when performing 4X over sampling?
a. 2
b. 3
c. 4
d. 5
Answer: B

26. A PAM source generates four symbols 3 V, 1 V, – 1 V and – 3 V with probabilities of 0.2, 0.3, 0.3 and 0.2 respectively. The variance for this source will be
a. 4.2 V
b. 3.2 V
c. 3.6 V
d. 4.6 V
Answer: A

27. The output equivalent circuit of following circuit is

a. INVERTER
b. AND
c. OR
d. NOR
Answer: C

28. A binary source in which 0’s occur 3 times as often as 1’s. Then its entropy in bits/symbol will be
a. 0.75 bits/symbol
b. 0.25 bits/symbol
c. 0.81 bits/symbol
d. 0.85 bits/symbol
Answer: C

29. Maximum value of signal to noise ratio of an 8 bit ADC with an input range of 10 volts will be
a. 50 dB
b. 43.8 dB
c. 48.9 dB
d. 49.8 dB
Answer: D

30. The available power required at a receiver antenna I is 10-6 watts. Transmitting and receiving antennas have gain of 40 dB each. The carrier frequency is 4 GHz and the distance between them is 30 miles. The required transmitted power is
a. 0.64 Watts
b. 0.74 Watts
c. 0.78 Watts
d. 0.32 Watts
Answer: A

31. An FM signal at 10.7 MHz IF needs to be digitized for demodulation in a digital domain. If the bandwidth of this signal is 200 kHz, the maximum usable sampling frequency is
a. 200 kHz
b. 600 kHz
c. 400 kHz
d. 800 kHz
Answer: C

32. A satellite system employs QPSK modulation with 40% excess bandwidth per carrier including guard band. The voice channels use 64 kbps PCM coding. The number of channels supported by 36 MHz bandwidth of the transponder in bandwidth limited case will be
a. 1000
b. 800
c. 900
d. 600
Answer: B

33. Hamming codes are used for
a. Burst error correction
b. Signal error correction
c. Both a and b
d. None of the above
Answer: B

34. Which statements is correct for Schottkey diode?
a. Current voltage characteristics is totally different than that of a PN junction diode
b. The current is controlled by the diffusion of minority carriers
c. The current results from the flow of minority carriers
d. The storage time ts is almost zero
Answer: D

35. Photo diodes operate at
a. Forward bias
b. Breakdown region
c. Reverse bias
d. Saturation region
Answer: C

36. The dynamic resistance of diode varies as
a. 1/I2
b. 1/I
c. I
d. I2
Answer: B

37. In a PN diode, with the increase in reverse bias, the reverse current
a. Increases
b. Decreases
c. Remain constant
d. Uncertain
Answer: C

38. The Nyquist filter has impulse response given by
Answer: A

39. The figure shown is a signal space diagram for
a. Quadrature QPSK
b. Binary FSK
c. Bi-phase PSK
d. MSK
Answer: B

40. Negative feedback in amplifiers
a. Improves the signal to noise ratio at the input
b. improves the signal to noise ratio at the output
c. Does not affect the signal to noise ratio at the output
d. All of the above
Answer: B

41. Output response of a diode clipper circuit shown in figure will be
Answer: A

42. For an N-channel MOSFET, if conduction parameter (kn) is 0.249 mA/V2, gate to source voltage VQS is 2 VTN, where VTN = 0.75 volts. The current will be
a. 0.160 mA
b. 0.150 mA
c. 0.140 mA
d. 0.170 mA
Answer: C

43. If α = 0.98, ICO = 6 µA and IR = 100 µA for a transistor, then the value of IC will be
a. 2.3 mA
b. 3.1 mA
c. 4.6 mA
d. 5.2 mA
Answer: D

44. A unit step voltage 2u(t-θ) is applied in a series RC circuit with R = 2Ω, C = 1 F. assuming zero initial conditions, find i(t).
Answer: C

45. The auto correlation of a wide sense stationary random process is given by e-2IτI. The peak value of the spectral density is
a. 2
b. 1
c. e-1/2
d. e
Answer: C

46. Which of the following gives piezo electric effect?
a. µ metal
b. PVDF
c. Saphire
d. Ferrite
Answer: B

47. The mean free path for electron drift increases with
a. Purity
b. Strain hardening
c. Elastic modules
d. None of the above
Answer: A

48. Pure metals generally have
a. High conductivity & Low temperature coefficient
b. High conductivity & High temperature coefficient
c. Low conductivity & Zero temperature coefficient
d. Low conductivity & High temperature coefficient
Answer: B

49. A typical optical fiber has
a. High refractive index core & low refractive index cladding
b. Low refractive index core & High refractive index cladding
c. Uniform refractive index core surrounded by variable refractive index cladding
d. None of the above
Answer: B

50. The ceramic materials are
a. Inorganic substances
b. Brittle
c. Good thermal insulators
d. All of the above
Answer: A

51. The best definition of a superconductor is
a. It is a material showing perfect conductivity and Meissner effect below a critical temperature
b. It is conductor having zero resistance
c. It is a perfect conductor with highest diamagnetic susceptibility
d. It is a perfect conductor but becomes resistive when the current density through it exceeds a critical value
Answer: A

52. A periodic function of half wave symmetry is necessarily
a. An even function
b. An odd function
c. Neither odd nor even
d. Both odd and even
Answer: C

53. The Fourier transform of a Gaussian time pulse is
a. Uniform
b. A pair of impulses
c. Gaussian
d. Rayleigh
Answer: C

54. The covariance function Cx(τ) of a stationary stochastic process x(t) is said to be positive definite. This means that
Answer: A

55. If a vertical dipole antenna is used in conjunction with a loop antenna for direction finding, the field pattern obtained will be
Answer: A

56. The coding system typically used in digital telemetry is
a. PPM (pulse position modulation)
b. PAM (pulse amplitude modulation)
c. PCM (Pulse code modulation)
d. PDM (Pulse duration modulation)
Answer: C

57. The temperature coefficient of resistance for a thermistor is
a. Low and negative
b. Low and positive
c. High and negative
d. High and positive
Answer: C

58. Compared to field effect photo transistor, bipolar photo transistors are
a. More sensitive and faster
b. Less sensitive and slower
c. More sensitive and slower
d. Less sensitive and faster
Answer: A

59. A uniform plane wave in air impinge at 45o angle on a loss less dielectric material with dielectric constant ϵr. The transmitted wave propagates at a 30o direction with respect to the normal. The value of ϵr is
a. 1.5
b. √1.5
c. 2
d. √2
Answer: C

60. If a donor type impurity is added to the semiconductor, then at a given temperature, the Fermi level
a. Moves towards the center of the energy gap
b. Moves towards the valence band
c. Moves towards the conduction band
d. Doesn’t change
Answer: C

61. Which of the following statement is correct?
a. In semiconductors, electrons and holes move in an electric field and in the same direction
b. Electric field density is exactly equal to the sum of electric field intensity and polarization
c. Ampere’s circuital law states that the line integral of H about any closed path is exactly equal to the direct current enclosed by that path
d. None of the above
Answer: C

62. Magnetic field intensity (H) in A/m, with in a magnetic material where, M = 150 A/m, µ = 1.5 x 10-5 H/m, µr = 30:
a. 14.921
b. 14.138
c. 1.82
d. 13.715
Answer: D

63. A steel pipe is constructed of a material for which µr = 200 and σ = 5x106 mho/m. the outer and inner radii are 8 and 6 mm respectively and the length is 80m. If the total current carried by the pipe is 2 cos104πt Amp. Then the skin depth will be
a. 0.225 x 10-3 m
b. 0.300 x 10-3 m
c. 0.352 x 10-3 m
d. 0.125 x 10-3 m
Answer: A

64. A small amount of phosphorous is added to silicon so that here are 2.5x1017 conduction electrons per cubic meter and 9.0x1014 holes per cubic meter. Let µe = 0.13 m2/V-sec and µh = 0.05 m2/V-sec. The resistivity in Ω-m will be
a. 5.2072
b. 192.042
c. 129.02
d. 0
Answer: B

65. Silicon dioxide is used in ICs
a. Because it facilitates the penetration of diffurants
b. Because of its high heat conduction
c. To control the location of diffusion and to protect and insulate the Si surface
d. To control the concentration of diffurants
Answer: C

66. Evaluate the given integral.
Answer: B

67. Both transistor T1 and T2 in figure have a threshold voltage of 1 volt. The device parameters K1 and K2 of T1 and T2 are 36 µA/V2 and 9 µA/V2 respectively. The output voltage Vo is
a. 1 volt
b. 2 volt
c. 3 volt
d. 4 volt
Answer: C

68. A ramp input applied to a unity feedback system results in 5% steady state error. The type number and zero frequency gain of the system are
a. 1 and 20
b. 0 and 20
c. 0 and 1/20
d. 1 and 1/20
Answer: A

69. The magnitude of frequency response of an under sampled second order system is 5 at 0 rad/sec and peaks at 10/√3 at 5√2 rad/sec. the transfer function of the system is

Answer: A

70. The system with the open loop transfer function G(s)H(s) = 1/[s(s2 + s + 1)] has a gain margin of
a. – 6 dB
b. Zero
c. 3.5 dB
d. 6 dB
Answer: B

71. The value of k, for the given function, f(t)
a. 1
b. 2
c. 3
d. 4
Answer: D

72. A person on trip has a choice between private car and public transport. The probability of using a private car is 0.45. While using public transport, further choice available are bus and metro. Out of which the probability of commuting by a bus is 0.55. In such a situation, the probability (rounded up to two decimals) of using car, bus and metro respectively would be
a. 0.45, 0.30 and 0.25
b. 0.45, 0.25 and 0.30
c. 0.45, 0.55 and 0
d. 0.45, 0.35 and 0.20
Answer: A

73. A real root of equation x3 – 5x – 7 = 0 by the method of false position correct to three decimal places is
a. 2.7472
b. 2.084
c. 2.077
d. None of the above
Answer: A

74. Find the z-transform of cosh(nθ)
Answer: A

75. Newton – Raphson iteration formula for finding
Answer: C

76. The value of
Answer: B

77. Find the values of KD , KP and KI for PID controller respectively, whose characteristics equation has real roots at 10, ζ = 0.8 and ω= 2 rad/sec
a. 1.8, 8, 10
b. 1.8, 4, 5
c. 3.6, 8, 20
d. 1.8, 8, 20
Answer: A

78. The transfer function (1 + 0.5s) / (1 + s) represents a
a. Lag network
b. Lead network
c. Lag-lead network
d. Proportional controller
Answer: A

79. The wavelength of emitted radiation by electron while transmitting from one energy state of
–15 eV to other energy state of – 5 eV is
a. 1000Ao
b. 1240Ao
c. 1280Ao
d. 1300Ao
Answer: B

80. According to maximum power transfer theorem, maximum power transfer occurs when
a. Load R is equal to the half the R of the network
b. Load R is equal to twice the R of network
c. Load R is equal to the R of network looking back at it from voltage terminal
d. Load R is equal to the R of network looking back at it from load terminals with all sources being replaced by their respective internal resistance.
Answer: D