JEE Questions for Physics Communication System Quiz 8 - MCQExams.com

The maximum line-of-sight distance dM between two antennas having heights hT and hR above the earth is

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  • 2)
    Physics-Communication System-64268.png

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The frequency band used in the downlink of satellite communication is
  • 9.5 to 2.5 GHz
  • 896 to 901 MHz
  • 3.7 to 4.2 GHz
  • 840 to 935 MHz
  • 3.7 to 4.2 MHz
In amplitude modulation, the bandwidth is
  • Twice the audio signal frequency
  • Thrice the audio signal frequency
  • Thrice the carrier wave frequency
  • Twice the carrier wave frequency
  • Sum of audio signal frequency and carrier wave frequency
1000 kHz carrier wave is amplitude modulated by the signal frequency 200-4000 Hz. The channel width of this case is
  • 8 kHz
  • 4 kHz
  • 7.6 kHz
  • 3.8 kHz
  • 400 kHz
A radar has a power of 1 kW and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance upto which it can detect object located on the surface of the earth (Radius of earth = 6.4 x 106m) is
  • 80 km
  • 16 km
  • 40 km
  • 64 km
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
  • Yes
  • No
  • Information is not sufficient
  • 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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  • 48

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A photodetector is made from a semiconductor with Eg = 0.73 eV. What is the maximum wavelength, which it can detect?
  • 1000 nm
  • 1703 nm
  • 500 nm
  • 173 nm
A transmitter supplies 9 kW to the aerial when unmodulated. The power radiated when modulated to 40% is
  • 5 kW
  • 9.72 kW
  • 10 kW
  • 12 kW
The antenna current of an AM transmitter is 8 A when only carrier is sent but increases to 8.96 A when the carrier is sinusoidally modulated. The percentage modulation is
  • 50%
  • 60%
  • 65%
  • 71%
The maximum range, dmax, of radar is
  • Proportional to the cube root of the peak transmitted power
  • Proportional to the fourth root of the peak transmitted power
  • Proportional to the square root of the peak transmitted power
  • Not related to the peak transmitted power at all
In AM, the centpercent modulation is achieved when
  • Carrier amplitude = signal amplitude
  • Carrier amplitude ≠ signal amplitude
  • Carrier frequency = signal frequency
  • Carrier frequency ≠ signal frequency
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?
  • 70%
  • 65.4%
  • 94.4%
  • 25.5%
A 500 Hz modulating voltage fed into an FM generator produces a frequency deviation of 2.25 kHz. If amplitude of the voltage is kept constant but frequency is raised to 6 kHz then the new deviation will be
  • 4.5 kHz
  • 54 kHz
  • 27 kHz
  • 15 kHz
The bit rate for a signal, which has a sampling rate of 8 kHz and where 16 quantisation levels have been used is
  • 32000 bits/s
  • 16000 bits/s
  • 64000 bits/s
  • 72000 bits/s
Statement I Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals.
Statement II The state of ionosphere varies from hour to hour, day to day and season to season
  • Statement I is true, statement II is true; statement II is a correct explanation for statement I
  • Statement I is true, statement II is true; statement II is not a correct explanation for statement I
  • Statement I is true, statement II is false
  • Statement I is false, statement II is true
Statement I Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals.
Statement II The state of ionosphere varies from hour to hour, day to day and season to season.
  • Statement I is true, statement II is true; statement II is a correct explanation for statement I
  • Statement I is true, statement II is true; statement II is not a correct explanation for statement I
  • Statement I is true, statement II is false
  • Statement I is false, statement II is true
Assertion Diode lasers are used as optical sources in optical communication.
Reason Diode lasers consume less energy.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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 eritical frequency.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • If Assertion is false but Reason is true.
Assertion Short waves bonds are used for transmission of radio waves to a large distance.
Reason Short waves are reflected by ionosphere.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • If Assertion is false but Reason is true.
Assertion The electrical conductivity of earth\'s atmosphere decreases 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 ionisation of the atoms of the gases present there and pressure of gases decreases with increase in altitude.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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 wavelength.
Reason Shorter the wavelength, larger is the velocity of wave propagation.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • if both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • 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.
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of the Assertion.
  • If Assertion is true but Reason is false.
  • If the Assertion and Reason both are false.
  • If Assertion is false but Reason is true.
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