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JEE Questions for Physics Communication System Quiz 13 - MCQExams.com
JEE
Physics
Communication System
Quiz 13
Arrange the following communication frequency bands in the increasing order of frequencies 1. AM broadcast 2. Cellular mobile radio 3. FM broadcast 4. Television UHF 5. Satellite communication
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1 3 4 2 5
0%
1 2 3 4 5
0%
5 2 4 3 1
0%
1 3 2 4 5
The distance of coverage of a transmitting antenna is 12.8 km. Then, the height of the antenna is (Given that radius of earth = 6400 km)
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6.4 m
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12.8 m
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3.2 m
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16 m
The mobile telephones operate typically in the range of
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1–100 MHz
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100 – 200 MHz
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1000 – 2000 MHz
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800 – 950 MHz
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10 – 1000 kHz
A sky wave with a frequency 55 MHz is incident on D –¬region of earth\'s atmosphere at 45°. The angle of refraction is (electron density for D – region is 400 electrons/cm
3
)
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60°
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45°
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30°
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15°
In a diode AM–detector, the output circuit consists of R= 1 kΩ and C =10 pF. A carrier signal of 100 kHz is to be detected. Is it good
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Yes
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No
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Information is not sufficient
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None of the above
Consider an optical communication system operating at λ – 800 nm. Suppose, only 1% of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of 8 kHz
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4.8 × 108
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48
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6.2 × 108
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4.8 × 105
A photodetector is made from a semiconductor with E
g
= 0.73 eV. What is the maximum wavelength, which it can detect
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500 nm
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1000 nm
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1703 nm
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173 nm
An amplitude modulated wave is modulated to 50%. What is the saving in power if carrier as well as one of the side bands are suppressed
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70%
0%
65.4%
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94.4%
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25.5%
The audio signal used to modulate 60 sin (2π× 10
6
t) is 15 sin 300 πt. The depth of modulation is
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50%
0%
40%
0%
25%
0%
15%
The bit rate for a signal, which has a sampling rate of 8 kHz and where 16 quantization levels have been used is
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32000 bits/s
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16000 bits/s
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64000 bits/s
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72000 bits/s
Identify the incorrect statement from the following
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AM detection is carrier out using a rectifier and an envelop detector
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Pulse Position denotes the time of rise or fall of the pulse amplitude
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Modulation index µ is kept ≥ 1, to avoid distortion
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Facsimile (FAX) scans the contents of the document to create electronics signals
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Detection is the process of recovering the modulating signal from the modulated carrier wave
Assertion
Diode lasers are used as optical sources in optical communication.
Reason
Diode lasers consume less energy.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Television signals are received through sky-wave propagation.
Reason
The ionosphere reflects electromagnetic waves of frequencies greater than a certain critical frequency.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Electromagnetic waves with frequencies smaller than the critical frequency of ionosphere cannot be used communication using sky wave propagation.
Reason
The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Short waves bands are used for transmission of radio waves to a large distance.
Reason
Short waves are reflected by ionosphere.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
The electrical conductivity of earth\'s atmosphere decrease with altitude.
Reason
The high energy particles (i.e.,γ–rays and cosmic rays) coming from outer space and entering our earth\'s atmosphere cause ionization of the atoms of the gases present there and pressure of gases decreases with increase in altitude.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
The electromagnetic waves of shorter wavelength can travel longer distances on earth\'s surface than those of longer wavelengths.
Reason
Shorter the wavelength, larger is the velocity of wave propagation.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
The surface wave propagation is used for medium wave band and for television broadcasting.
Reason
The surface waves travel directly from transmitting antenna to receiver antenna through atmosphere.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
The television broadcasting becomes weaker with increases distance.
Reason
The power transmitted from TV transmitter varies inversely as the distance of the receiver
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Microwave propagation is better than the sky wave propagation.
Reason
Microwaves have frequencies 100 to 300 GHz, which have very good directional properties
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Satellite is an ideal platform for remote sensing.
Reason
Satellite in polar orbit can provide global coverage or continuous coverage of the fixed area in geostationary configuration.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Fax is a modulating and demodulating device.
Reason
It is necessary for exact reproduction of a document.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
A dish antenna is highly directional.
Reason
This is because a dipole antenna is omni directional.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Microwave communication is preferred over optical communication.
Reason
Microwaves provide large number of channels and bandwidths compared to optical signals.
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0%
If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
0%
If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
0%
If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
A portable AM radio set must be kept horizontal to receive the signals properly.
Reason
Radio waves are polarized electromagnetic waves.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Optical fibre communication has immunity to cross-talk.
Reason
Optical interference between fibres is zero.
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
Assertion
Transmission Electron Microscope (TEM) provides two dimensional images.
Reason
Scanning Electron Microscope (SEM) provides three dimensional images
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If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
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If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
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If Assertion is true but Reason is false.
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If the Assertion and Reason both are false.
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If Assertion is false but Reason is true.
A ground receiver station is receiving a signal at 5 MHz and transmitted from a ground transmitted at a height of 300 m, located at a distance of 100 km from the receiver station. The signal is coming via. (Radius of earth = 6.4 × 10
6
m. N
max
of ionosphere =10
12
m
3
)
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Space wave
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Sky wave propagation
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Satellite transponder
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All of these
In the given detector circuit, the suitable value ofcarrier frequency is
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<< 109 Hz
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<< 105 Hz
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>> 109 Hz
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None of these
The impedance of coaxial cable, when its inductance is 0.40 µH and capacitance is 1 × 10
–11
F, can be
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2 × 102 Ω
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100 Ω
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3 × 103 Ω
0%
3 × 10–2 Ω
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