# 90 TOP Electronics and Communication Engineering VIVA Interview Questions and Answers for freshers and experienced pdf free Download

Electronics & Communication Engineering VIVA Objective type questions, Electronics & Communication Engineering LAB VIVA Questions and Answers for experienced

## Electronics & Communication Engineering LAB VIVA Questions and Answers List

1.The impedance curve of an R-L-C network cuts the frequency axis only when the frequency is such that
(a) XL=XC
(b) XL=XC=0
(c) R=0 and XL=XC
(d) none of these
Ans: c

2.In a semiconductor diode, P-side is grounded and N-side is applied a potential of -5V through a resistance of 100 ohms. the diode shall
(a) conduct fully
(b) not conduct
(c) conduct partially
(d) none of these
Ans: a

3. the junction diode’s capacitance that is made use of in varactors is known as
(a) transition capacitance
(b) diffusion capacitance
(c) space charge capacitance
(d) inter-electrode capacitance.
Ans: a

4. when current through a zener diode increases by a factor of 2, voltage across its terminals
(a) is halved
(b) is doubled too
(c) is practically unchanged
(d) none of these
Ans: c

5. SCRs are connected in series to enchance
(a) their overall dv/dt rating
(b) their voltage ratings
(c) their current handling capabilities
(d) none of these
Ans: b

6. the condition that decides the oscillator’s out put frequency is :
(a) loop gain should at least be unity
(b) loop phase-shift should be zero or integral multiple of 2p radians
(c) loop gain should be precisely unity
(d) loop phase-shift should be precisely zero radian.
Ans: b

7. most popular oscillator configuration for audio applications is :
(a) Hartley oscillator
(b) colpitt’s oscillator
(c) wein-bridge oscillator
(d) R-C phase shift oscillator.
Ans: c

8. pick the odd-one out :
(a) Hartley oscillator
(b) collpitt oscillator
(c) clap oscillator
(d) wein bridge oscillator
Ans: d

9.the output voltage at no load in an unregulated power supply is the same as its output voltage at rated load current. its internal resistance is therefore
(a) extremely small
(b) zero
(c) infinite
(d) extremely large.
Ans: b

10. mark the rectifier circuit that produces the least ripple
(a) single rectifier,half wave, single phase
(b) four rectifiers,full wave,single phase
(c) two rectifiers,full wave,single phase
(d) six rectifiers,full wave,three phase.
Ans: d

11. indicate the false statement
(a) closed loop gain is always less than the open loop gain.
(b) input impedance is always greater than the out put impedance
(c) the open loop gain falls to zero decibel at a frequency equal to unity gain crossover frequency
(d) closed loop bandwidth is always greater than the open loop bandwidth
Ans: d

12. one of the following statements in reference to a unity gain noninverting buffer using an opamp is in correct. identify this statement
(a) it has extremely high input impedance,much higher than even its open loop input impedance
(b) its input impedance is very high almost approaching its open loop input impedance magnitude
(c) the voltage gain is unity.
(d) the inputis applied to the non-inverting input
(e) the feed back magnitude is 100 percent.
Ans: b

13.the SLEW RATE specification of an opamp is usually measured in
(a) microvolts per second
(b) volts per microsecond
(c) decibels
(d) volts per microvolt
Ans: b

14. a given opamp has an open loop gain of 110dB and a CMRR rating of 106dB. what should be the open loop common mode gain of this op-amp?
(a) it cannot be determined from the given data
(b) 4dB
(c) 216 dB
(d) 110Db
Ans: b

15. in a 555 astable multivibrator operating from Vcc of 15V, the output wave from duty cycle is 0.4 (duty cycle = ON-time/total time period.) the circuit is slightly modified with the capacitor now charging from a voltage of 30V rather than Vcc. the duty cycle of the output waveform in the modified circuit will
(a) remain unchanged
(c) be approximately 0.2
(d) none of these
Ans: c

16. the pulse width in a 555 monostable multivibrator is given by
(a)t = 0.69 RC
(b)t = 1.1 RC
(c)t = RC
(d) none of these
Ans: b

17. in the astable mode of operation of IC 555, the timing capacitor always charges between
(a) 0 and 1/3 Vcc
(b) 1/3 Vcc and 2/3Vcc
(c) 0 and 2/3 Vcc
(d) 0 and Vcc
Ans: b

18.when a PLL is being used as an FM demodulator,the demodulated signal appears at
(a) the output of phase comparator
(b) the output of low pass filter
(c) the VCO output
(d) none of these.
Ans: b

19.”A NOR gate is equivalent to a bubbled AND gate”. this statement is an outcome of
(a) demorgan’s theorems
(b) involution law
(c) absorption law
(d) idempotent law
Ans: a

20.for one of the following conditions, clocked j-k flip flop can be used as DIVIDE BY 2 circuit where the pulse train to be divided is applied at clock input.
(a) J=1, K=1 and the flip flop should have active HIGH inputs
(b) J=1, K=1 and the flip flop should have active LOW inputs
(c) J=0, K=0 and the flip flop should have active high inputs
(d) J=1, K=1 and the flip flop should be a negative edge triggered one.
Ans: a

21. in a presettable, clearable positive edge triggered J-K flip flop, the Q output when the flip flop is clocked for
J=1,K=0,preset=1 and clear = 0 will be
(a) 1
(b) 0
(c) indeterminate
(d) complement of what it was at the time of clocking
(assume all the inputs to be active LOW inputs).
Ans: b

22. A 4-bit circulating register is initially set to 0001(1 is the true output of the first flip flop and represents LSB).
4-bit number preset in the register at the end of 16 clock pulses is
(a) 0001
(b) 0010
(c) 0100
(d) 1000
Ans: a

23. a shift counter comprising of 5 flip flops with an inverse feedback from the output of the MSB flip flop to the input of the LSB flip flop is a
(a) divide by 32 counter
(b) divide by 10 counter
(c) 5-bit shift register
(d) modulus-5 counter
Ans: b

24. number of comparators needed to build a 6-bit simultaneous A/D converter is
(a) 63
(b) 64
(c) 7
(d) 6
Ans: a

25. the average conversion time in a 4-bit counter type A/D converter run by a 10 MHZ clock shall be
(a) 8ms
(b) 400ns
(b) 800ns
(d) none of these
Ans: c

26. out of the following,the fastest A/D converter type is
(a) counter type A/D converter
(b) successive approximation type A/D converter
(c) dual slope integrating type A/D converter
Ans: b

27. if the received carrier frequency in an AM communications broadcast receiver is changed from 560kHz to 1120kHz the resonant frequency of the IF tuned circuits
(a) would have to be changed from 455Khz to 910kHz.
(b) would remain unchanged at 455kHz
(c) would also change in the same proportion but in the opposite direction.
Ans: b

(a) RF Section
(b) IF Section
(c) Mixer
Ans: b

29. antenna reciprocity is put to use in :
(d) none of these
Ans: c

30. an antenna behaves as a resonant circuit only when its length is :
(a) l/2
(b) l/4
(c) l/2 or its integral multiple
(d) none of these
Ans: c

31. an antenna should have :
(a) a very high SWR
(b) a very small SWR
(c) a moderate value of SWR
(d) none of these
Ans: a

32. the input impedance of a centre-fed half-wave dipole is :
(a) 300 W
(b) 288 W
(c) 75 W
(d) none of these
Ans: c

33. an antenna is radiating 100 watts and is drawing 2A from the transmitter, its radiation resistance is :
(a) 100 W
(b) 50 W
(c) 25 W
(d) none of these
Ans: c

34.smaller the beamwidth angle :
(a) smaller the directivity
(b) higher the directivity
(c) higher the power gain
(d) none of these
Ans: b

35. in a broadside array :
(a) maximum reception is in a direction perpendicular axis
(b) maximum reception is along the axis
(c) the directional pattern is undirectional
(d) none of these
Ans: a

36. in an end-fire array:
(a) maximum reception is along the axis
(b) maximum reception is perpendicular to the axis
(c) directional pattern is bi-directional
(d) none of these
Ans: a

37.the simplest parasitic array comprises of :
(a) two elements
(b) three elements
(c) five elements
(d) none of these
Ans: a

38. a yagi-antenna in horizontal plane :
(a) produces an end-fire pattern
(c) produces a figure eight pattern
(d) none of these
Ans: b

39. a television transmitting antenna should have :
(a) an omnidirectional pattern
(b) an end-fire pattern
(d) none of these
Ans: a

40. by increasing the height of the TV receiving antenna :
(a) the range of TV broadcast decreases
(b) signal pick up is less
(c) antenna may fail to receive the signal
(d) the range of TV broadcast increases
(e) none of these
Ans: d

41. a transmission line is having a reflection coefficient of 1/3 when terminated in a certain load. it is SWR is :
(a) 2
(b) ½
(c) 3
(d) none of these
Ans: a

42. medium wave travel as :
(a) space waves
(b) surface waves
(c) sky waves
(d) none of these
Ans: b

43. high frequency waves follow :
(a) the ground wave propagation
(b) the line of sight direction
(c) the ionosphere propagation
(d) the bend along the curvature of earth.
Ans: c

44. VHF waves travel as :
(a) space waves
(b) sky waves
(c) ground waves
(d) surface waves
Ans: a

45. UHF waves travel as :
(a) space waves
(b) surface waves
(c) ground waves
(d) sky waves
Ans: a

46. during night- time the ionosphere consists of :
(a) D,E,F1,F2 layers
(b) D,E,F1, layers
(c) E,F1,F2 layers
(d) E and F2 layers.
Ans: d

47. if the heights of the transmitting and receiving antennas are doubled, the range of TV broadcast:
(a) decrease by a factor of 2
(b) increases by a factor of 2
(c) increases by factor of 1:414
(d) is reduced to one-fourth.
Ans: c

48. in electromagnetic waves, polarisation is :
(a) due to transverse nature of waves
(b) always vertical in isotropic medium
(c) due to longitudinal nature of waves
(d) caused by reflection of waves
Ans: a

49. the UHF waves are also called as :
(a) millimeter waves
(b) centimeter waves
(c) long waves
(d) short waves
Ans: a

50. a transmission line has an SWR of 3 when terminated in a certain load. the reflection co-efficient is
(a) 3
(b) ½
(c) 1/3
(d) none of these
Ans: b

51. lines of constant resistance on a smith chart are
(a) parallel to each other
(b) all circle tangent to each other on one extreme
(c) arcs of circles
(d) none of these
Ans: b

52. electromagnetic wave in which the electric field is entirely transverse to the direction of propogation is known as
(a) TE wave
(b) TEM wave
(c) TM wave
(d) TE10 wave
(e) TE11 wave
Ans: a

53. one of the following modes does not exist in wave guides
(a) TE10 mode
(b) TE11 mode
(c) TEM mode
(d) TM01 mode
Ans: c

54. the dominant mode in rectangular waveguides is the
(a) TE10 mode
(b) TM01 mode
(c) TE11 mode
(d) TM11 mode.
Ans: a

55. for a rectangular wave guide with a=2 cm and b=1 cm, the cut-off wavelength for TE10 mode will be
(a) 2 cm
(b) 1 cm
(c) 4 cm
(d) none of these.
Ans: c

56. in a radar system, a rotating system is used to
(a) determine the target range
(b) determine the target cross-section
(c) determine the target bearing
(d) none of these
Ans: c

57. a device that is used to detect objects under water is known as
(b) sonar
(c) MTI
Ans: b

58. a radar system that can determine the range of the target along with the target velocity is
(b) MTI
Ans: b

59. market the correct expression
(a) Doppler shift = 2vrf/c
(b) Doppler shift = 2cf/v4
(c) Doppler shift = 2f/cv4
(d) Doppler shift = vrf/c
Ans: a

60. in a TV picture tube, the deflection of electron beam is achieved by :
(a) electrostatic means
(b) electromagnetic means
(c) electrostatic means for horizontal deflection and electromagnetic means for vertical deflection
(d) electromagnetic means for horizontal deflection and electrostatic means for vertical deflection
Ans: b

61. identify secondary colours
(a) red,green,blue
(b) red,cyan,yellow
(c) cyan,yellow,magneta
(d) magneta,cyan,green
Ans: c

62. luminance signal is expressed by
(a) Y = R+G+B
(b) Y=0.3 R +0.59G+0.11B
(c) Y = 0.5 R + 0.5 G + 0.5 B
(d) Y=0.59R + 0.3 G +0.11B
Ans: b

63. one of the following camera tubes is based on photo emissive principle
(a) vidicon
(b) saticon
(c) image orthicon
(d) newvicon
Ans: c

64. pick the odd one out
(a) vidicon camera
(b) plumbicon camera
(c) CCD camera
(d) saticon camera
Ans: c

65. transient response of a control system is the one
(a) which approaches zero when the time approaches infinity
(b) which does not depend up on time
(c) which is time dependent
(d) none of these
Ans: a

66. a causal system is the one in which the output depends up on
(a) input as well as output
(b) present and past inputs
(c) present as well as future inputs
(d) present and past inputs and past outputs
Ans: b

67. area under a unit impulse function is
(a) infinity
(b) zero
(c) unity
(d) none of these
Ans: c

68. stability of a control system can be determined from one of the following responses.
(a) impulse response
(b) step response
(c) ramp response
Ans: a

69. a feed back control system has a transfer function given by
P (s) = (s+1)(s+3)/s(s+2)(s+4) it’s a
(a) type-5 system
(b) type -2 system
(c) type-3 system
(d) type-4 system
Ans: b

70. gain margin can be determined from the root locus plot by
(a) value of gain factor (K) at imaginary crossover/design value of (k)
(b) design value of gain factor (k) / value of gain factor (k) at imaginary crossover
(c) value of gain factor (K) at real axis crossover/design value of (k)
(d) none of these
Ans: a

71. a higher value of gain factor (K) at the imaginary axis crossover of the root locus part of a control system
(a) brings it closer to instability
(b) takes it farther from instability
(c) is always undesirable
(d) none of these
Ans: b

72. for drawing the root locus plot of a certain closed loop control system, one needs to know
(a) only the open loop transfer function of the system
(b) the closed loop transfer function
(c) the closed loop system pole-zero map
(d) the open loop transfer function, gain and phase margins
Ans: a

73. when the PLL is being used as a frequency multiplier or a frequency divider, the output is taken from
(a) the VCO input
(b) the output of phase comparator
(c) the VCO output
(d) LPF output
Ans: c

74. the essential building blocks of a phase locked loop are
(a) the VCO , the phase comparator and the error amplifer
(b) the VCO, the phase comparator and the low pass filter
(c)the VCO, the low pass filter and the error amplifer
(d) the phase comparator,the low pass filter and the error amplifier
(e) the phase comparator and the VCO
Ans: b

75. while connecting SCRs in series, the individual SCRs chosen for the purpose should have closely matched
(a) di/dt rating
(b) reverse biased characteristics
(c) forward and reverse blocking characteristics
(d) forward ON-state characteristics
Ans: c

76. while connecting SCRs in parallel, the SCRs to be connected in parallel should have closely matched
(a) forward ON- state characteristics
(b) forward and reverse OFF- state characteristics
(c) forward OFF-state and ON-state characteristics
(d) SCRs cannot be connected in parallel
Ans: a

77. a UJT relaxation oscillator circuit produces a sawtooth like waveform
(a) at B1 terminal
(b) at B2 terminal
(c) across the capacitor
(d) none of these
Ans: c

78. in half wave SCR power control circuit, if the firing angle is 300 c, then for one complete cycle of operation,the load gets power for
(a) 600
(b) 1500
(c) 3300
(d) 300
Ans: b

79. most popular oscillator configuration for audio applications is :
(a) Hartley oscillator
(b) colpitt’s oscillator
(c) wein-bridge oscillator
(d) R-C phase shift oscillator.
Ans: c

80. the multivibrator characterized by one quasi-stable state is:
(a) bistable multivibrator
(b) monostable multi vibrator
(c) astable multivibrator
(d) Schmitt trigger
Ans: b

81. one of the following can be used to generate a pulse when ever triggered:
(a) flip-flop
(b) monostable multivibrator
(c) astable multivibrator
(d) Schmitt trigger
Ans: b

82. one of the following opamp type number is a comparator
(a) LM710
(b) LM 741
(c) LM748
(d) LM747
Ans: a

83. the operation of a thermocouple is based on :
(a) seebeck effect
(b) peltier effect
(c) Thomson effect
Ans: a

84. a high Q-factor coil has:
(a) a flat response
(b) a response with slightly lower bandwidth
(c) a higher power loss
(d) a peaked response
Ans: d

85.lower the thermal resistances (junction-to-case-to-ambient) of a bipolar transistor,
(a) lower is the power dissipation capability for a given ambient temperature
(b) higher is the power dissipation capability for a given ambient temperature
(c) higher is the probability of the device going to thermal runaway
(d) better is its high frequency performance
Ans: b

86. pulse communication system that is inherently highly immune to noise is
(a) PCM
(b) PAM
(c) PPM
(d) PAM
Ans: a

87. the characteristic impedance of a certain transmission line section is 75 ohms. if the length of the line is doubled, the characteristic impedance would
(a) reduce to half
(b) double too
(c) increase four times
(d) characteristic impedance is independent of length of line.
Ans: d

88. one of the following is a tracking radar
(d) secondary surveillance radar JNTU World
Ans: c

89.the radar that has a higher range resolution and that makes use of matched filter design is