Electronics & Communication Engineering-90 Most Important MCQ PDF

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
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
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
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
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
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.
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
8.   pick the odd-one
out :
(a) Hartley oscillator (b) collpitt oscillator
(c) clap oscillator (d) wein bridge oscillator
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
(a) extremely small (b) zero
(c) infinite (d) extremely large.
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.
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

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 per cent.
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
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
15.    in a 555 astable
multivibrator operating from Vcc of 15V, the output wave from duty cycle is 0.4 (duty
= 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 (b) become about 0.6
(c) be approximately 0.2 (d) none of these
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
17.    in the astable mode of operation of IC 555, the timing
capacitor always charges
(a) 0 and 1/3 Vcc (b) 1/3 Vcc and 2/3Vcc
(c) 0 and 2/3 Vcc (d) 0 and Vcc
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.
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
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.
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).

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
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
24.    number of
comparators needed to build a 6-bit simultaneous A/D converter is (a) 63 (b) 64
(c) 7 (d) 6
25.    the average
conversion time in a 4-bit
counter type A/D converter run by a 10 MHZ clock shall
(a)   8ms (b) 400ns
(b)   800ns (d) none
of these
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
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.
28.    in a broadcast communication receiver,most of the receiver selectivity is achieved in
(a) RF Section (b) IF Section (c) Mixer
29.    antenna
reciprocity is put to use in :
(a) television broadcast systems (b) commercial radio
(c) radar systems (d) none of these
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
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
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
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

34.  smaller the beamwidth
angle :
(a) smaller the directivity (b) higher the directivity
(c) higher the power gain (d) none of these
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
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
37.  the simplest parasitic
array comprises of :
(a) two elements (b) three elements
(c) five elements (d) none of these
38.    a
yagi-antenna in horizontal plane :
(a) produces an end-fire pattern (b) produces a
broadside  pattern
(c) produces a figure eight pattern (d) none of these
39.    a
television transmitting antenna should have :
(a) an omnidirectional
pattern (b) an end-fire pattern
(c) a broadside pattern (d) none of these
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
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
42.    medium wave travel as :
(a) space waves (b) surface waves
(c) sky waves (d) none of these
43.    high frequency waves follow :
(a) the ground wave propagation (b) the line of sight
(c) the ionosphere propagation (d) the bend along the
curvature of  earth.

44.    VHF waves
travel as :
(a) space waves (b) sky waves
(c) ground waves (d) surface waves
45.    UHF waves travel as :
(a) space waves (b) surface waves
(c) ground waves (d) sky waves
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.
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
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
49.    the UHF waves are also called as :
(a) millimeter waves (b) centimeter waves
(c) long waves (d) short waves
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
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
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
53.    one of the following
modes does not exist in wave guides
(a) TE10 mode (b) TE11 mode
(c) TEM mode (d) TM01 mode
54.    the
dominant mode in rectangular waveguides is the
(a) TE10 mode (b) TM01 mode
(c) TE11 mode (d) TM11 mode.
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.

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
57.    a device
that is used to detect objects under water is known as
(a) radar (b) sonar
(c) MTI (d) pulse compression radar
58.    a radar
system that can determine the range of the target along with the target
velocity is
(a) CW radar (b) MTI
(c) pulse radar (d)
Doppler radar
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
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
61.    identify
secondary colours
(a) red,green,blue (b) red,cyan,yellow
(c) cyan,yellow,magneta (d) magneta,cyan,green
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
63.    one of the following camera tubes is based on photo emissive
(a) vidicon (b) saticon
(c) image orthicon (d) newvicon
64.    pick the odd one out
(a) vidicon camera (b) plumbicon camera
(c) CCD camera (d) saticon camera
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
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

67.    area under
a unit impulse function is
(a) infinity (b) zero (c) unity (d) none of these
68.    stability of a control
system can be determined from one of the following
(a) impulse response (b) step response
(c) ramp response (d) steady state response
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
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
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
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
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
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
(e)  the phase comparator and the VCO
75.    while connecting SCRs in series,
the individual SCRs chosen for the purpose
should have closely
(a) di/dt rating (b) reverse biased characteristics
(c) forward and reverse blocking characteristics (d)
forward ON-state characteristics
76.    while connecting SCRs in parallel,
the SCRs to be connected
in parallel should have closely
(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

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
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
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
80.    the
multivibrator characterized by one quasi-stable state is:
(a) bistable multivibrator (b) monostable multi vibrator
(c) astable multivibrator (d) Schmitt trigger
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
82.    one of the
following opamp type number is a comparator
(a) LM710 (b) LM 741
(c) LM748 (d) LM747
83.    the
operation of a thermocouple is based on :
(a) seebeck effect (b) peltier effect
(c) Thomson effect (d) faraday’s laws
84.    a high
Q-factor coil has:
(a) a flat response (b) a response with slightly lower
(c) a higher power loss (d) a peaked response
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
86.    pulse
communication system that is inherently highly immune to noise is
(a) PCM (b) PAM (c) PPM (d) PAM
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.
88.    one of the
following is a tracking radar
(a) monostatic radar
(b) bistatic radar
(c) monopulse radar (d) secondary surveillance radar

89.  the radar that has a
higher range resolution and that makes use of matched filter design is
(a) pulse compression radar (b) MTI
(c) pulse Doppler radar
(d) monopulse radar
90.    in the
radar guidance of missiles where the missile has its own radar and it extracts
the tracking data from the target reflected energy, the technique is known as
(a) command guidance (b) beam rider guidance (c)homming
guidance (d) none of these