Electronics-Comunication-Engineering-

                      BSNL JAO Recruitment Examination Previous Paper

1. Reactive current through the inductive load produces-

a) Magnetic field

b) Electric field

c) Super magnetic field

d) None

2. When a piece of copper and another of germanium are cooled from room temperature to 80⁰ K then the resistance of -

a) each of them increases

b) each of them decreases

c) copper increases and germanium decreases

d) copper decreases and germanium increases

3. A capacitance transducer has two plates of area 5 cm² each separated by an air gap of 2mm. Displacement sensitivity in pF /cm due to gap change would be -

a) 11.1

b) 44.2

c) 52.3

d) 66.3

4.  The critical angle in degrees, for an electromagnetic wave passing from Quartz (m = m_0, Î=4Î_o) into air is-

a) 15

b)30

c)45

d)90

5. When an RC driving point impedance function has zeros at s= -2 and s=-5 then the admissible poles for the function would be –

a) s = 0; s = -6

b) s = -1; s = -3

c) s = 0; s = -1

d) s = -3; s = -4

6. A capacitor used for power factor correction in single- phase circuit decreases –

a) the power factor

b) the line current

c) Both the line current and the power factor

d) the line current and increases power factor

7. The unit of inductance is –

a) ohm

b) inductive reactance

c) inducta

d) Henry

8. Which type of by-pass capacitor works best at high frequencies –

a) electrolytic

b) mica

c) ceramic

d) plexiglass

9. The usual value of the surge impedance of a telephone line is –

a) 600 W

b) 500 W

c) 75 W

d) none

10. Telemetering is a method of –

a) counting pulses, sent over long distances

b) transmitting pictures from one place to another

c) transmitting information concerning a process over a distance

d) None

11. In an unbiased P-N junction thickness of depletion layer is of the order of –

a) 0.005 mm

b) 0.5 mm

c) 5 mm

d) 10^-10 m

12. One of the semiconductor device, which behaves like two SCRs is–

a) UJT

b)  triac

c) JFET

d) MOSFET

13. The following, which is not an advantage of semiconductor strain gauges as compared to conventional strain gauges, is –

a) excellent hysterists characteristics

b) least sensitive to temperature changes

c) high fatigue life

d) smaller size

14. The fundamental ripple frequency of a half wave 3F rectifier with a 3F supply of frequency 50 Hz is –

a) 150 Hz

b) 50 Hz

c) 100 Hz

d) 250 Hz.  

15. For an FR biased PNP transistor –

a) base is negative with respect to emitter

b) collector is positive with respect to emitter

c) collector is a little more positive than base

d) base is a little less positive with respect to emitter than collector

16. With normal operation of a JFET one can get I_Dss –

a) the maximum drain current

b) the minimum drain current

c) normal drain current

d) none

17. An SCR is a semiconductor device made up of –

a) Four N type layers

b) Two P types and three N type layers

c) Two P type and two N type layers

d) Three P type and one N type layers

18. For a UJT, if R₁ = resistance from emitter to base 1, R₂ = resistance from emitter to the base 2 and R_BB = R₁ +R₂ then the intrinsic stand off ratio (h) is –

a)

b)

c)  

d)

19. As the drain voltage is increased for a junction FET in the pinch off region then the drain current –

a) becomes zero

b) abruptly decreases

c) abruptly increases

d) remains constant

20. 20 When the energy gap of a semiconductor is 1.1eV then it would be –

a) opaque to the visible light

b) transparent to the visible light

c) transparent to the infrared radiation

d) opaque to the infrared radiation

21.The equivalent capacitance across ab will be –

 d.0

22. In the following fig. the power dissipated is maximum when the value of R_x is –

a) 33.4 K

b) 17.6 K

c) 10 K

d) 5 K

23. The transfer function of a low pass RC network is –

24. The total capacitance across points 'a' and 'b' in the given figure is –

a) 1.66 mF

b) 2.66 mF

c) 3.5 mF

d) 4.5 mF

25. The load resistance needed to extract maximum power from the following circuit is –

a) 2W

b) 9W

c) 6W

d) 18W

26. Which one of the following conditions for z parameters would hold for a two port network containing linear bilateral passive circuit elements –

a) z₁₁ = z₂₂

b) z₁₂z₂₁ = z₁₁z₂₂

c) z₁₁z₁₂ = z₂₂z₂₁

d) z₁₂ = z₂₁

27. In the network shown, the switch is opened at t = 0. Prior to that, the network was in  the steady state, Vs(t) at t = 0 is –

a) 0

b) 5V

c) 10V

d) 15V

28. Which of the following statements are correct –

1. Tellegen's theorem is applicable to any lumped network

2. The reciprocity theorem is applicable to linear bilateral networks.

3. Thevenin's theorem is applicable to two terminal linear active networks.

4. Norton's theorem is applicable to two terminal linear active networks.

a) 1, 2 and 3

b) 1, 2, 3 and 4

c) 1, 2 and 4

d) 3 and 4

29. Which one of the following transfer functions represents the critically damped system ?

30. When the respective coil impedance of the circuit shown in the fig. is are Z₁ = (5 + j8)W and Z₂=(3+j8) then the input impedance of the circuit will be –

a) (8 + 16j)W

b) (2 + j0)W

c) (15 + 64j)W

d) (8 + 0j)W

31. One of the following statement which is not correct -

a) In case of an antenna, the radiation resistance and loss resistance are not two different quantities.

b) The loss resistance includes loss by eddy currents, improper earth connections, insulation leakages etc) but not I²R losses

c) Radiation resistance varies directly as square root of the frequency

d) None of the above

32. Ultraviolet radiation emitted when electron jumps from an outer stationary orbit to -.

a) first stationary orbit

b) second stationary orbit

c) third stationary orbit

d) fourth stationary orbit

33. When the signal is propogated in a waveguide which has a full wave of electric intensity change between the two farther walls and no component of the electric field in the direction of propogation then the mode is –

a) TE₁₁

b) TE₁₀

c) TM₂₂

d) TE₂₀

34. Consider the following statements pertaining to parabolic antenna -

1.It is commonly used above 1GHz

2. It get’s circularly polarized

3. It’s radiation pattern is highly directional

4. It’s radiation pattern is cardiod

of these statements-

a)  1,2 and 4 are correct

b) 1 and 3 are correct

c)  1,2 and 3 are correct

d) 2 and 4 are correct

35. When a vertical dipole antenna is used in conjunction with a loop antenna for direction finding, then the field pattern obtained will be-

36. When one end of a loss less transmission line of length 3/8 l and characteristic impedance R₀ is short circuited and the other end is terminated in Ro then the impedance at l/8 away from the end terminated in R₀ is-

a)  Zero

b) R₀

c)  R₀/2

d) Infinite

37. For transmission of wave from a dielectric permittivity Î₁ into dielectric medium of lower permittivity Î₂ (Î₁ > Î₂) the critical angle of incidence Qc ( relative to the interface ) is given by -

38. A transmission line has primary constants R, L, G and C and secondary constants Z₀ and g (= a + jb) if the line is loss less then .

39. The intrinsic impedance of a free space is-

40. One of the following which is a low gain but omni directional antenna is-

a) discone

b) log-periodic

c) loop

d) helical

41. Electronic voltmeters have –

a) high input impedance

b) low input impedance

c) zero input impedance

d) none

42. Which of the following statement about impulse voltage is true ?

a) An impulse voltage is an unidirectional voltage.

b) In chopped impulse voltage, flashover does not occur.

c) Time taken to rise is exactly equal to the time taken to fall.

d) RMS value of impulse voltage is always less than 50% of average value.

43. The precision of an instrument indicates its ability to reproduce a certain reading with a given –

a) drift

b) resolution

c) shift.

d) consistency

44. In heterodyne digital conductor, the input signal is heterodyned to a –

a) higher frequency

b) lower frequency

c) both a and b)

d) none

45. In a digital measuring device, if the input electrical signal is in the frequency range dc to f_max Hz, then it must be sampled at a rate of –

a) f_max times/sec

b) f_max times/ses

c) every 2f_max/sec

d) 2 f_max times/sec .

46. Moving Iron intruments measures the rms value of –

a) a direct quantity

b) an alternating quantity

c) a virtual quantity.

d) none.

47. One of the following intruments which is used almost exclusively to measure radio frequency current is-

a) Moving coil meter

b) Rectifier-type moving coil meter

c) Iron-vane meter

d) Thermocouple meter.

48. A good ohmic contact on a p- type semiconductor chip is formed by introducing –

a) gold as an impurity below the contact

b) a high concentration of donors below the contract

c) a high concentration of acceptors below the contact

d) a thin insulator layer between the metal and semiconductor.

49. The use of thermocouple meters for ac measurement leads to a meterscale which is –

a) linear

b) square law

c) logarithmic

d) exponential

50. If low pressure of the order of 10^-6mm of Hg is to be measure then the instrument of choice would be-

a) compound pressure gauge

b) thermocouple vacuum gauge

c) pirani gauge

d) ionization type vacuum gauge

51. The equivalent circuit of a resistor is shown in the given figure. The resistor will be non inductive if –

a)

b)

c)

d)

52. SCR turns OFF from conducting state to blocking state on –

a) reducing gate current

b) reversing gate voltage

c) reducing anode current below holding current value

d) applying ac to the gate

53. Static V-I characteristics of an SCR with different gate drives applied to the gate are indicated by-

a) I₉₂ > I ₉₁ > I ₉₀

b) V₉₂  > V₉₁ > V₉₀

c) P₉₂  > P₉₁ > P₉₀

d) either a or b

54. Each diode of a 3 phase, 6-pulse bridge diode rectifier conducts for-

a) 60^o

b) 120⁰

c) 180⁰

d) 90⁰  

55. A load, consisting of R = 10W and wL = 10W is being fed from 230 V, 50 Hz source through a 1 phase voltage controller. For a firing angle delay of 30⁰ , the rms value of load current would be-

                 a) 23 A

56. The total number of SCRs conducting simultaneously in a 3 phase full converter with overlap considered has the sequence of-

a) 3,3, 22

b) 3, 3, 3, 2

c) 3, 2, 3, 2

d) 2, 2, 2, 3

57. A single phase voltage controller, using two SCRs in antiparallel is found to be operating as a controlled rectifier. This is because

a) load is R and pulse gating is used

b) load is R and high frquendy carrier gating is used

c) load is RL and pulse gating is used

d) load is RL and continuous gating is used

58. The inverse Fourier Transform of 

59. In a GTO anode current begins to fall when gate current-

a) is negative peak at time t = 0

b) is negative peak at t = shortage period t_s

c) just begins to become negative at t = 0

d) is negative peak at t = (t_s + fall time)

60. Power amplifiers and Audio use

a) Ferrite core

b) Air core

c) Solid iron core

d) Laminated iron core

61. The amplifiers which are inserted at intervals amplify the signal and compensate for transmission less on the cable are called-

a) Line amplifiers

b) Equalizing amplifiers

c) Rep eaters

d) Compandors

62. A solid state device named TRIAC acts as a ----- switch

a) 3 terminal unidirectional

b) 2 terminal unidirectional

c) 3 terminal bi-directional

d) 2 terminal bi-directional

63. Identify the fastest logic circuit when speed of operation is concerned-

a) TTL

b) RTL

c) DTL

d) ATL

64. An amplifier CE is characterized by-

a) Low voltage gain

b) Moderate power gain

c) Very high output impedance

d) Signal phase reversal

65. The standard symbol for EX-OR gate is –

a)         

b)

c)       

d)

66. Boolean algebra is based on –

a) numbers

b) logic

c) truth

d) symbols

67. Magnetic amplifiers are used for –

a) voltage amplification

b) power amplification

c) current amplification

d) frequency amplification

68. Number of resistors required for an N bit D/A converter in R-2R ladder D/A converter is-

a) 4N

b) 1N

c) 3N

d) 2N

69. 'Not allowed' condition in NAND gate SR flip flop is –

a) s = 0, R = 0

b) s = 1, R = 1

c) s = 0, R = 1

d) s = 1, R = 0

70.In a PID controlles the transfer function G(s) is

71. A time invariant linear stable system is forced with an input x(t) = A sin wt under steady state conditions, the output  Y(t) of the system will be –

a) A sin (wt + f),where  f = tan^-1|G(jw) |

b) A G (jw) | A sin [wt + G(jw)]

c) | G (jw) | A sin [2 wt + G (jw)]

d) | G (jw) A sin [wt + G (jw)]

     x(t)-------G(s)---------y(t)

72. Mark the wrong statement for two phase servo motor –

a) The rotor diameter is small

b) The rotor resistance is low

c) The applied voltages are seldom balanced

d) The torque speed characterstic are linear.

73. The gain phase plot of open loop transfer function of four different systems labelled A, B, C, and D

are shown in the figure. The correct sequence of the increasing order of stability of the four systems will be-

a) A, B, C, D

b) D, C, B, A

c) B, A, D, C,

d) B, C, D, A

74. A unity feedback system has G(S) = .  In the loot locus, the break away point occurs between

a) S = 0 and –1

b) S = -1 and ¥

c) S = -1 and –2

d) S =-2 and – ¥

75. Twice in a year a few minute disturbance occurs in space communication during sun-blinding when --- are in line

a) Sun and satellite

b) Sun and earth station

c) Satellite and earth station

d) Sun, satellite and earth station

76. The traffic handling capacity of an Earth station on the up link depends on-

a) It’s EIRP

b) Satellite antenna gain

c) Noise associated with the satellite

d) All of the above

77. A supergroup pilot is –

a) applied at each multiplexing bay

b) used to regulate the gain of individual repeaters

c) applied at each adjustable equalizer

d) fed in at a GTE

78. If the antenna diameter in a radar system is increased by a factor of 4, the maximum range will be increased by a factor of

a) Ö2

b) 2