Communication Systems, Laser Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In short wave communication which of the following
frequencies will be reflected back by the ionospheric layer,
having electron density 10
11
 per m
3
.
(a) 2.84  MHz (b) 10.42 MHz
(c) 12.24 MHz (d) 18.1 MHz
Q.2 In an amplitude modulated wave for audio frequency of
500 cycle/second, the appropriate carrier frequency will
be
(a) 50 cycles/sec (b) 100 cycles/sec
(c) 500 cycles/sec (d) 50, 000 cycles/sec
Q.3 Range of frequencies allotted for commercial FM radio
broadcast is
(a) 88 to 108 MHz (b) 88 to 108 kHz
(c) 8 to 88 MHz (d) 88 to 108 GHz
Q.4 The process of superimposing signal frequency (i.e. audio
wave) on the carrier wave is known as
(a) Transmission (b) Reception
(c) Modulation (d) Detection
Q.5 The characteristic impedance of a coaxial cable is of the
order of
(a) 50 W (b) 200 W
(c) 270 W (d) None of these
Page 2


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In short wave communication which of the following
frequencies will be reflected back by the ionospheric layer,
having electron density 10
11
 per m
3
.
(a) 2.84  MHz (b) 10.42 MHz
(c) 12.24 MHz (d) 18.1 MHz
Q.2 In an amplitude modulated wave for audio frequency of
500 cycle/second, the appropriate carrier frequency will
be
(a) 50 cycles/sec (b) 100 cycles/sec
(c) 500 cycles/sec (d) 50, 000 cycles/sec
Q.3 Range of frequencies allotted for commercial FM radio
broadcast is
(a) 88 to 108 MHz (b) 88 to 108 kHz
(c) 8 to 88 MHz (d) 88 to 108 GHz
Q.4 The process of superimposing signal frequency (i.e. audio
wave) on the carrier wave is known as
(a) Transmission (b) Reception
(c) Modulation (d) Detection
Q.5 The characteristic impedance of a coaxial cable is of the
order of
(a) 50 W (b) 200 W
(c) 270 W (d) None of these
2
DPP/ P 59
Q.6 If 
1
m and 
2
m are the refractive indices of the materials of
core and cladding of an optical fibre, then the loss of light
due to its leakage can be minimised by having
(a)
12
m >m (b)
12
m <m
(c)
12
m =m (d) None of these
Q.7 Maximum usable frequency (MUF) in F-region layer is x,
when the critical frequency is 60 MHz and the angle of
incidence is 70
o
. Then x is (cos 70° = 0.34)
(a) 150 MHz (b) 170 MHz
(c) 175 MHz (d) 190 MHz
Q.8 A laser is a coherent source because it contains
(a) many wavelengths
(b) uncoordinated wave of a particular wavelength
(c) coordinated wave of many wavelengths
(d) coordinated waves of a particular wavelength
Q.9 A laser beam is used for carrying out surgery because it
(a) is highly monochromatic
(b) is highly coherent
(c) is highly directional
(d) can be sharply focussed
Q.10 Laser beams are used to measure long distances because
(a) they are monochromatic
(b) they are highly polarised
(c) they are coherent
(d) they have high degree of parallelism
Q.11 An oscillator is producing FM waves of frequency
2 kHz with a variation of 10 kHz . What is the modulating
index?
(a) 0.20 (b) 5.0 (c) 0.67 (d) 1.5
Q.12 If 
a
f and f
f
 represent the carrier wave frequencies for
amplitude and frequency modulations respectively, then
(a)
af
ff >
(b)
af
ff <
(c)
af
ff =
(d)
af
ff ³
Q.13 An antenna is a device
(a) that converts electromagnetic energy into radio
frequency signal
(b) that converts radio frequency signal into
electromagnetic energy
(c) that converts guided electromagnetic waves into free
space electromagnetic waves and vice-versa
(d) None of these
Q.14 While tuning in a certain broadcast station with a receiver,
we are actually
(a) varying the local oscillator frequency
(b) varying the frequency of the radio signal to be picked
up
(c) tuning the antenna
(d) None of these
Q.15 In a communication system, noise is most likely to affect
the signal
(a) At the transmitter
(b) In the channel or in the transmission line
(c) In the information source
(d) At the receiver
Q.16 In an FM system a 7 kHz signal modulates 108 MHz
carrier so that frequency deviation is 50 kHz . The carrier
swing is
(a) 7.143 (b)8
(c) 0.71 (d) 350
Q.17 The phenomenon by which light travels in an optical fibres
is
(a) Reflection
(b) Refraction
(c) Total internal reflection
(d) Transmission
Q.18 In frequency modulation
(a) The amplitude of modulated wave varies as frequency
of carrier wave
(b) The frequency of modulated wave varies as amplitude
of modulating wave
(c) The amplitude of modulated wave varies as amplitude
of carrier wave
(d) The frequency of modulated wave varies as frequency
of modulating wave
Page 3


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In short wave communication which of the following
frequencies will be reflected back by the ionospheric layer,
having electron density 10
11
 per m
3
.
(a) 2.84  MHz (b) 10.42 MHz
(c) 12.24 MHz (d) 18.1 MHz
Q.2 In an amplitude modulated wave for audio frequency of
500 cycle/second, the appropriate carrier frequency will
be
(a) 50 cycles/sec (b) 100 cycles/sec
(c) 500 cycles/sec (d) 50, 000 cycles/sec
Q.3 Range of frequencies allotted for commercial FM radio
broadcast is
(a) 88 to 108 MHz (b) 88 to 108 kHz
(c) 8 to 88 MHz (d) 88 to 108 GHz
Q.4 The process of superimposing signal frequency (i.e. audio
wave) on the carrier wave is known as
(a) Transmission (b) Reception
(c) Modulation (d) Detection
Q.5 The characteristic impedance of a coaxial cable is of the
order of
(a) 50 W (b) 200 W
(c) 270 W (d) None of these
2
DPP/ P 59
Q.6 If 
1
m and 
2
m are the refractive indices of the materials of
core and cladding of an optical fibre, then the loss of light
due to its leakage can be minimised by having
(a)
12
m >m (b)
12
m <m
(c)
12
m =m (d) None of these
Q.7 Maximum usable frequency (MUF) in F-region layer is x,
when the critical frequency is 60 MHz and the angle of
incidence is 70
o
. Then x is (cos 70° = 0.34)
(a) 150 MHz (b) 170 MHz
(c) 175 MHz (d) 190 MHz
Q.8 A laser is a coherent source because it contains
(a) many wavelengths
(b) uncoordinated wave of a particular wavelength
(c) coordinated wave of many wavelengths
(d) coordinated waves of a particular wavelength
Q.9 A laser beam is used for carrying out surgery because it
(a) is highly monochromatic
(b) is highly coherent
(c) is highly directional
(d) can be sharply focussed
Q.10 Laser beams are used to measure long distances because
(a) they are monochromatic
(b) they are highly polarised
(c) they are coherent
(d) they have high degree of parallelism
Q.11 An oscillator is producing FM waves of frequency
2 kHz with a variation of 10 kHz . What is the modulating
index?
(a) 0.20 (b) 5.0 (c) 0.67 (d) 1.5
Q.12 If 
a
f and f
f
 represent the carrier wave frequencies for
amplitude and frequency modulations respectively, then
(a)
af
ff >
(b)
af
ff <
(c)
af
ff =
(d)
af
ff ³
Q.13 An antenna is a device
(a) that converts electromagnetic energy into radio
frequency signal
(b) that converts radio frequency signal into
electromagnetic energy
(c) that converts guided electromagnetic waves into free
space electromagnetic waves and vice-versa
(d) None of these
Q.14 While tuning in a certain broadcast station with a receiver,
we are actually
(a) varying the local oscillator frequency
(b) varying the frequency of the radio signal to be picked
up
(c) tuning the antenna
(d) None of these
Q.15 In a communication system, noise is most likely to affect
the signal
(a) At the transmitter
(b) In the channel or in the transmission line
(c) In the information source
(d) At the receiver
Q.16 In an FM system a 7 kHz signal modulates 108 MHz
carrier so that frequency deviation is 50 kHz . The carrier
swing is
(a) 7.143 (b)8
(c) 0.71 (d) 350
Q.17 The phenomenon by which light travels in an optical fibres
is
(a) Reflection
(b) Refraction
(c) Total internal reflection
(d) Transmission
Q.18 In frequency modulation
(a) The amplitude of modulated wave varies as frequency
of carrier wave
(b) The frequency of modulated wave varies as amplitude
of modulating wave
(c) The amplitude of modulated wave varies as amplitude
of carrier wave
(d) The frequency of modulated wave varies as frequency
of modulating wave
DPP/ P 59
3
Q.19 Audio signal cannot be transmitted because
(a) The signal has more noise
(b) The signal cannot be amplified for distance
communication
(c) The transmitting antenna length is very small to design
(d) The transmitting antenna length is very large and
impracticable
Q.20 For sky wave propagation of a 10 MHz signal, what should
be the minimum electron density in ionosphere
(a)
123
~ 1.2 10 m
-
´
(b)
63
~10m
-
(c)
143
~10m
-
(d)
223
~10m
-
Q.21What should be the maximum acceptance angle at the
aircore interface of an optical fibre if 
1
n and 
2
n are the
refractive indices of the core and the cladding, respectively
(a)
1
21
sin ( /) nn
-
(b)
1 22
12
sin nn
-
-
(c)
1 2
1
tan
n
n
-
éù
êú
ëû
(d)
1 1
2
tan
n
n
-
éù
êú
ëû
DIRECTIONS (Q.22-Q.24) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.22 In which of the following remote sensing technique is used?
(1) Forest density
(2) Pollution
(3) Wetland mapping
(4) Medical treatment
Q.23 What type of modulation is not employed in India for radio
transmission?
(1) A mixture of both frequency and pulse modulation.
(2) Pulse modulation
(3) Frequency modulation
(4) Amplitude modulation
Q.24Which of the following are the characteristics of Laser
beams?
(1) They are monochromatic
(2) They are coherent
(3) They have high degree of parallelism
(4) They are not monochromatic
DIRECTIONS (Q.25-Q.27) : Read the passage given below
and answer the questions that follows :
The electron density of a layer of ionosphere at a height 150 km
from the earth's surface is 9 × 10
9 
per m
3
. For the sky
transmission from this layer up to a range of 250 km,
Q.25 The critical frequency of the layer is
(a) 2 Hz (b) 2.7 Hz
(c) 2.78 kHz (d) 2.7 MHz
Q.26 Maximum usable frequency is
(a) 3.17 Hz
(b) 3.17 × 10
6 
HZ
(c) 3.17×10 
3
 Hz
(d) 3.17 × 10
10
Hz
Q.27 Angle of incidence of this layer is
(a) 0° (b) sec
–1
(1.51)
(c) sec
–1
(1.17) (d) 37°
Page 4


DIRECTIONS (Q.1-Q.21) : There are 21 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 In short wave communication which of the following
frequencies will be reflected back by the ionospheric layer,
having electron density 10
11
 per m
3
.
(a) 2.84  MHz (b) 10.42 MHz
(c) 12.24 MHz (d) 18.1 MHz
Q.2 In an amplitude modulated wave for audio frequency of
500 cycle/second, the appropriate carrier frequency will
be
(a) 50 cycles/sec (b) 100 cycles/sec
(c) 500 cycles/sec (d) 50, 000 cycles/sec
Q.3 Range of frequencies allotted for commercial FM radio
broadcast is
(a) 88 to 108 MHz (b) 88 to 108 kHz
(c) 8 to 88 MHz (d) 88 to 108 GHz
Q.4 The process of superimposing signal frequency (i.e. audio
wave) on the carrier wave is known as
(a) Transmission (b) Reception
(c) Modulation (d) Detection
Q.5 The characteristic impedance of a coaxial cable is of the
order of
(a) 50 W (b) 200 W
(c) 270 W (d) None of these
2
DPP/ P 59
Q.6 If 
1
m and 
2
m are the refractive indices of the materials of
core and cladding of an optical fibre, then the loss of light
due to its leakage can be minimised by having
(a)
12
m >m (b)
12
m <m
(c)
12
m =m (d) None of these
Q.7 Maximum usable frequency (MUF) in F-region layer is x,
when the critical frequency is 60 MHz and the angle of
incidence is 70
o
. Then x is (cos 70° = 0.34)
(a) 150 MHz (b) 170 MHz
(c) 175 MHz (d) 190 MHz
Q.8 A laser is a coherent source because it contains
(a) many wavelengths
(b) uncoordinated wave of a particular wavelength
(c) coordinated wave of many wavelengths
(d) coordinated waves of a particular wavelength
Q.9 A laser beam is used for carrying out surgery because it
(a) is highly monochromatic
(b) is highly coherent
(c) is highly directional
(d) can be sharply focussed
Q.10 Laser beams are used to measure long distances because
(a) they are monochromatic
(b) they are highly polarised
(c) they are coherent
(d) they have high degree of parallelism
Q.11 An oscillator is producing FM waves of frequency
2 kHz with a variation of 10 kHz . What is the modulating
index?
(a) 0.20 (b) 5.0 (c) 0.67 (d) 1.5
Q.12 If 
a
f and f
f
 represent the carrier wave frequencies for
amplitude and frequency modulations respectively, then
(a)
af
ff >
(b)
af
ff <
(c)
af
ff =
(d)
af
ff ³
Q.13 An antenna is a device
(a) that converts electromagnetic energy into radio
frequency signal
(b) that converts radio frequency signal into
electromagnetic energy
(c) that converts guided electromagnetic waves into free
space electromagnetic waves and vice-versa
(d) None of these
Q.14 While tuning in a certain broadcast station with a receiver,
we are actually
(a) varying the local oscillator frequency
(b) varying the frequency of the radio signal to be picked
up
(c) tuning the antenna
(d) None of these
Q.15 In a communication system, noise is most likely to affect
the signal
(a) At the transmitter
(b) In the channel or in the transmission line
(c) In the information source
(d) At the receiver
Q.16 In an FM system a 7 kHz signal modulates 108 MHz
carrier so that frequency deviation is 50 kHz . The carrier
swing is
(a) 7.143 (b)8
(c) 0.71 (d) 350
Q.17 The phenomenon by which light travels in an optical fibres
is
(a) Reflection
(b) Refraction
(c) Total internal reflection
(d) Transmission
Q.18 In frequency modulation
(a) The amplitude of modulated wave varies as frequency
of carrier wave
(b) The frequency of modulated wave varies as amplitude
of modulating wave
(c) The amplitude of modulated wave varies as amplitude
of carrier wave
(d) The frequency of modulated wave varies as frequency
of modulating wave
DPP/ P 59
3
Q.19 Audio signal cannot be transmitted because
(a) The signal has more noise
(b) The signal cannot be amplified for distance
communication
(c) The transmitting antenna length is very small to design
(d) The transmitting antenna length is very large and
impracticable
Q.20 For sky wave propagation of a 10 MHz signal, what should
be the minimum electron density in ionosphere
(a)
123
~ 1.2 10 m
-
´
(b)
63
~10m
-
(c)
143
~10m
-
(d)
223
~10m
-
Q.21What should be the maximum acceptance angle at the
aircore interface of an optical fibre if 
1
n and 
2
n are the
refractive indices of the core and the cladding, respectively
(a)
1
21
sin ( /) nn
-
(b)
1 22
12
sin nn
-
-
(c)
1 2
1
tan
n
n
-
éù
êú
ëû
(d)
1 1
2
tan
n
n
-
éù
êú
ëû
DIRECTIONS (Q.22-Q.24) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.22 In which of the following remote sensing technique is used?
(1) Forest density
(2) Pollution
(3) Wetland mapping
(4) Medical treatment
Q.23 What type of modulation is not employed in India for radio
transmission?
(1) A mixture of both frequency and pulse modulation.
(2) Pulse modulation
(3) Frequency modulation
(4) Amplitude modulation
Q.24Which of the following are the characteristics of Laser
beams?
(1) They are monochromatic
(2) They are coherent
(3) They have high degree of parallelism
(4) They are not monochromatic
DIRECTIONS (Q.25-Q.27) : Read the passage given below
and answer the questions that follows :
The electron density of a layer of ionosphere at a height 150 km
from the earth's surface is 9 × 10
9 
per m
3
. For the sky
transmission from this layer up to a range of 250 km,
Q.25 The critical frequency of the layer is
(a) 2 Hz (b) 2.7 Hz
(c) 2.78 kHz (d) 2.7 MHz
Q.26 Maximum usable frequency is
(a) 3.17 Hz
(b) 3.17 × 10
6 
HZ
(c) 3.17×10 
3
 Hz
(d) 3.17 × 10
10
Hz
Q.27 Angle of incidence of this layer is
(a) 0° (b) sec
–1
(1.51)
(c) sec
–1
(1.17) (d) 37°
4
DPP/ P 59
DIRECTIONS (Qs. 28-Q.30) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.28 Statement-1 : Television signals are not received through
sky-wave propagation.
Statement-2 : The ionosphere reflects electromagnetic
waves of frequencies greater than a certain critical
frequency.
Q.29Statement-1 : The electromagnetic waves of shorter
wavelength can travel longer distances on earth’s surface
than those of longer wavelengths.
Statement-2 : Shorter the wavelength, the larger is the
velocity of wave propagation.
Q.30 Statement-1 : A dish antenna is highly directional.
Statement-2 : This is because a dipole antenna is omni
directional.