JEE Main Physics - Principles of Communication
Exam Duration: 60 Mins Total Questions : 30
A modulator
- (a)
generates constant frequency radiowaves
- (b)
generates variable frequency radiowaves
- (c)
improves signal-to-noise ratio
- (d)
improves thermal stablity
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
In amplitude modulation :
A. amplitude of a carrier wave is varied by signal voltage
B. frequency of the carrier wave remains unchanged
C. the wave shape of the modulated signal is different from that of the modulating signal
D. amplitude of the modulated wave varies at the modulating frequency.
- (a)
if A, B, C are correct
- (b)
if B, C, D are correct
- (c)
if C, D, A are correct
- (d)
All the correct
With 100% modulation in an AM wave, the tatio of sideband power to the total power is
- (a)
2/3
- (b)
1/3
- (c)
1/2
- (d)
1/4
For a 100% modulated A. M. wave, if the total power is 1200 W, power transmitted at each sideband is
- (a)
400 W
- (b)
800 W
- (c)
200 W
- (d)
300 W
The medium wave broadcast signals may get propagated via ionosphere. This happens
- (a)
both during day and night
- (b)
only during day
- (c)
only during night
- (d)
during day in winter and during night in summer
The absorption of radiowaves by the atmosphere depends upon the
- (a)
distance from the transmitter
- (b)
wave polarisation
- (c)
frequency of the waves
- (d)
polarisation of the absoubed waves
Voice frequency range in telephone system is restricted to about
- (a)
0 to 4000 Hz
- (b)
0 to 3400 Hz
- (c)
100 to 3600 Hz
- (d)
300 to 3400 Hz
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
The T.V. transmission tower in Delhi has a height of 240 m. The distance up to which the broadcast can be received is [given the radius of earth = 6400 km]
- (a)
50 km
- (b)
55 km
- (c)
60 km
- (d)
80 km
The emission line width will be narrowest for a
- (a)
Ruby laser
- (b)
He-Ne laser
- (c)
LED
- (d)
Hetrojunction laser
Amongst different types of fibres, sigle-mode step-index fibre has
- (a)
highest data rate
- (b)
lowest attenuation
- (c)
highest thickness
- (d)
both (a) and (b)
Inter model dispersion results from the fact that the light waves propagate through a fibre
- (a)
in different modes
- (b)
along different routes
- (c)
as a group of frequencies
- (d)
with same velocity
The structure of an optical fibre consists of
- (a)
multimode step-index
- (b)
graded index
- (c)
single-mode step-index
- (d)
all of the above
Till recently, electronic communication was accomplished by sending electrical signals through copper cables. Howeve, optical fibre communication, instead of electrical signals, uses
- (a)
light signals
- (b)
analog signals
- (c)
digital signals
- (d)
unmodulated signals
An optical fibre excels at rejecting
- (a)
electromagnetic interference
- (b)
radio-frequancy interference
- (c)
crossstalk
- (d)
all of the above
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
A plastic-clad fibre has similar characteristics as an all-glass fibre except that it is more sensitive to which kind of damage :
- (a)
chemical
- (b)
moisture
- (c)
corrosion
- (d)
abrasive
The numerical aperture of an optical fibre depends on
A. core refractive index
B. cladding refractive index
C. critical angle
Mark :
- (a)
if A, B are correct only
- (b)
if B, C are correct only
- (c)
if A, C are correct only
- (d)
if A, B, C all are correct
Very high-speed telephone line systems operate at more than
- (a)
1 GBd
- (b)
2 GBd
- (c)
3 GBd
- (d)
5 GBd
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
Choose INCORRECT statement :
- (a)
The optic fibres have greater information carrying capacities than metallic conductors
- (b)
The optic fibres are uneffected by lightning and sparking
- (c)
The optic fibres can carry large amount of information in either digital or analog form
- (d)
One of the important characteristecs is accurate signal radiation.
3-30 MHz frequency range is known as
- (a)
HF
- (b)
VHF
- (c)
UHF
- (d)
MF
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
Ozone layer above the earth's atmosphere will not
- (a)
prevent infrared radiations from sun reaching on the earth
- (b)
prevent infrared radiations originated from the earth from escaping the earth's atmosphere
- (c)
prevent ultraviolet rays from sun
- (d)
reflect back radio waves
Long distance short wave radio broadcasting uses
- (a)
ground wave
- (b)
sky wave
- (c)
direct wave
- (d)
space wave
In an amplitude modulated wave for audio frequency of 500 cycle/s, the appropriated carrier frequency will be
- (a)
50 cycle/s
- (b)
100 cycle/s
- (c)
500 cycle/s
- (d)
50000 cycle/s
A basic communication system consists of
(A) transmitter
(B) information source
(C) user of information
(D) receiver
Choose the correct sequence in which these are arranged in basic communication system.
- (a)
ABCD
- (b)
BADC
- (c)
BDAC
- (d)
All of these
What should be minimum length of antenna for efficient transmission of signals of wavelength \(\lambda \) ?
- (a)
\(\lambda \)/2
- (b)
\(\lambda \)/3
- (c)
\(\lambda \)/4
- (d)
\(\lambda \)/5