Physics - Principles of Communication
Exam Duration: 45 Mins Total Questions : 30
A short circuited, uniform, lossless transmission line of 0.04 wavelength long, acts almost like an ideal
- (a)
capacitor
- (b)
inductor
- (c)
series resonant circuit
- (d)
parallel resonant circuit
For a 100% modulated AM wave, if the carrier wave is suppressed, the amount of power saved will be
- (a)
33%
- (b)
50%
- (c)
67%
- (d)
75%
Choose the CORRECT statement :
- (a)
Modulation index and modulation factor indicate the same quantity
- (b)
In frequancy modulation, the frequency of the carrier wave varies according to the amplitude of modulating signal
- (c)
Frequency modulation is superior to amplitude modulation because of noise elimination.
- (d)
Only (a) and (c) are correct
In an amplitrde modulated wave, the amplitude of the side band is
- (a)
indepentent of the carrier amplitude
- (b)
indepentent of the modulation index
- (c)
carrier amplitude \(\times\) modulation index
- (d)
1/2 \(\times\) carrier amplitude \(\times\) modulation index
The FM broadcast band is from
- (a)
550 to 1600 kHz
- (b)
88 to 108 kHz
- (c)
88 to 108 MHz
- (d)
1600 kHz to 5975 MHz
Detection is done by
- (a)
radio receiver
- (b)
mixer
- (c)
local oscillator
- (d)
transmitter
In AM wave for frequency 1 kHz the carrier frequency will be
- (a)
100 Hz
- (b)
1 kHz
- (c)
10 kHz
- (d)
100 kHz
If VHF and higher frequency radiation is to be focussed into a beam by an antenna, the antenna diameter required for a given beam width
- (a)
increases as the square of frequency
- (b)
increases directly with frequency
- (c)
decreases with frequency
- (d)
is independent of frequency
Which of the ionospheric layers is termed as the Kennelly-Heaviside layer?
- (a)
D-layer
- (b)
E-layer
- (c)
F1-layer
- (d)
F2-layer
The term "critical frequency" denotes
- (a)
the lowest frequency that is reflected by the ionosphere
- (b)
the highest frequency that is reflected by the ionosphere at vertical incidence
- (c)
the lowest frequency by which communication is possible between two given points
- (d)
NONE OF THESE
For optical waveguiding, best result is obtained when the refractive indices for the core and cladding materials are, respectively
- (a)
1.5, 1.45
- (b)
1.5, 1.4
- (c)
1.4, 1.45
- (d)
1.4, 1.5
Fibre optic communication is preferred at a wavelength of 1.55 \(\mu m\) because at this wavelength.
- (a)
GaAs laser diodes have maximum power
- (b)
Optical fibre has minimum dispersion
- (c)
Optical fibre has minimum dispersion and attenuation
- (d)
Optical detectors have lowest noise
Optical fibres whether made of glass or plastic, are
- (a)
fragile
- (b)
brittle
- (c)
insulators
- (d)
leaky
The main energy losses in an optical fibre consists of
- (a)
material loss
- (b)
loss due to light scattering
- (c)
band loss
- (d)
all of the above
An all-pllastic fibre is strong mechanically as compared to an all-glass fibre but has
A. higher loses
B. lower bandwidth
C. lower tensile strength
Mark
- (a)
If A is correct only
- (b)
If B is correct only
- (c)
If A, B is correct only
- (d)
If A, C is correct only
In an optical fibre, the propagation angle of light must be equal to or less than the
- (a)
acceptance angle
- (b)
critical angle
- (c)
refraction angle
- (d)
incidence angle
Choose INCORRECT statement :
- (a)
The core of an optical fibre and its cladding have the same optical characteristec
- (b)
Cladding of a glass fibre reduces energy loss from it
- (c)
The basic material for glass fibres is silicon oxide
- (d)
Optical fibres do not radiate energy carried by them
Choose CORRECT statement :
- (a)
In a fibre optic communication system, transmission is more secure and private
- (b)
Fibre optic transmission is immune to electromagnetic interference
- (c)
Fibre optic communication particularly in voice-telephone applications is largely digital
- (d)
ALL OF THE ABOVE
Choose INCORRECT statement :
- (a)
For overall performance in terms of data rate and attenuation, the single-mode step-index fibre has the best characteristics
- (b)
In a step-index fibre, the refractive index changes in step fashion from the centre of the fibre to its cladding
- (c)
As compared to single-mode fibres, multimode fibres have the worst performance characteristtics
- (d)
Multifibre cables are not suited for trunk transmission links in which many messages travel the same route
Choose INCORRECT statement :
- (a)
Usually, the losses in an optical fibre are expressed in decibel per kilometer
- (b)
As compared to an all glass fibre, an all-plastc fibre has poorer transmission characterstics
- (c)
All-plastic fibres have lower bandwidth than all-glass fibres
- (d)
Optical fibres are good conductors of electricity
For VHF television broadcasting, the frequency employed is generally
- (a)
54-72 MHz
- (b)
420-890 MHz
- (c)
540-1600 kHz
- (d)
88-108 kHz
The radio waves of frequency 30 MHz to 300 MHz belong to
- (a)
high frequency band
- (b)
very high frequency band
- (c)
ultra high frequency band
- (d)
super high frequency band
In an AM wave for audio frequency of 3400 cycle/s, the appropriate carrier frequency will be
- (a)
1000 Hz
- (b)
34000 MHz
- (c)
60000 Hz
- (d)
800000 Hz
The maximum peak to peak voltage of an AM wire is 24 mV and the minimum peak to peak voltage is 8 mV. The modulation factor is
- (a)
10%
- (b)
20%
- (c)
25%
- (d)
50%
An amplitude modulated wave is modulated to 50%. What is the saving in power, if carrier as well as one of the sidebands are suppressed?
- (a)
70%
- (b)
65.4%
- (c)
94.4%
- (d)
25.5%
The carrier frequency generated by a tank circuit containing 1 nF capacitor and \(10\mu H\) inductor is
- (a)
1592 Hz
- (b)
1592 MHz
- (c)
1592 kHz
- (d)
159.2 Hz
A male voice after modulation transmission sounds like that of female to the receiver. The problem is due to
- (a)
poor selection of modulation index (selected o <.... < 1)
- (b)
poor bandwidth selection of amplifiers
- (c)
poor selection of carrier frequency
- (d)
loss of energy in transmission
Match the communication services given in Column I with their frequency range given in Column II and select the correct option from the choices given below
Column I | Column II | ||
A. | FM broadcast | 1. | 76-88 MHz |
B. | Television | 2. | 3.7-6.4 GHz |
C. | Satellite communication | 3. | 88-108 MHz |
- (a)
A B C 1 2 3 - (b)
A B C 3 1 2 - (c)
A B C 3 2 1 - (d)
A B C 1 3 2
A diode detector is used to detect and amplitude modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance 100 \(k\Omega \) . Find the maximum modulated frequency which could be detected by it.
- (a)
10.62 MHz
- (b)
10.61 kHz
- (c)
5.31 MHz
- (d)
5.31 kHz