JEE Questions for Physics Communication System Quiz 12 - MCQExams.com

The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to
  • h1/2
  • h
  • h3/2
  • h2
Sinusoidal carrier voltage of amplitude 50 V is amplitude voltage of frequency 10 modulation. The lower frequencies in kHz are
  • 1490, 1510
  • 1510, 1490

  • Physics-Communication System-64363.png

  • Physics-Communication System-64364.png
What is the modulation index of an over modulated wave
  • 1
  • Zero
  • < 1
  • > 1
If fa and ff represent the carrier wave frequencies for amplitude and frequency modulations respectively, then
  • fa>ff
  • faf
  • fa =ff
  • fa ≥ff
Which of the following is the disadvantage of FM over AM
  • Larger band width requirement
  • Larger noise
  • Higher modulation power
  • Low efficiency
If a number of sine waves with modulation indices n1, n2, n3 ....modulate a carrier wave, then total modulation index (n) of the wave is
  • n1 + n2... + 2 (n1 + n2 ...)
  • 2)
    Physics-Communication System-64367.png

  • Physics-Communication System-64368.png
  • None of the above
What type of modulation is employed in India for radio transmission
  • Amplitude modulation
  • Frequency modulation
  • Pulse modulation
  • None of the above
While tuning in a certain broadcast station with a receiver, we are actually
  • Varying the local oscillator frequency
  • Varying the frequency of the radio signal to be picked up
  • Tuning the antenna
  • None of the above
Monochromatic light of wavelength 667 nm is produced by a helium neon laser. The power emitted is 9 mW. The number of photons arriving per sec. on the average at a target irradiated by this beam is
  • 9 × 1017
  • 3 × 1016
  • 9 × 1015
  • 3 × 1019
Let A= light obtained by stimulated and B= light obtained by spontaneous emission, then
  • A is incoherent, B is incoherent
  • A is incoherent, B is coherent
  • A is coherent, B is coherent
  • A is coherent, B is incoherent
In an FM system a 7 kHz signal modulates 108 MHz carrier so that frequency deviation is 50 kHz. The carrier swing is
  • 7.143
  • 8
  • 0.71
  • 350
Audio signal cannot be transmitted because
  • The signal has more noise
  • The signal cannot be amplified for distance communication
  • The transmitting antenna length is very small to design
  • The transmitting antenna length is very large and impracticable
In which of the following remote sensing technique is not used
  • Forest density
  • Pollution
  • Wetland mapping
  • Medical treatment
For sky wave propagation of a 10 MHz signal, What should be the minimum electron density in ionosphere
  • ~1.2 × 1012 m–3
  • ~106 m–3
  • ~1014 m–3
  • ~1022 m–3
What should be the maximum acceptance angle at the aircore interface of an optical fibre ifn1 and n2 are the refractive indices of the core and the cladding,respectively

  • Physics-Communication System-64373.png
  • 2)
    Physics-Communication System-64374.png

  • Physics-Communication System-64375.png

  • Physics-Communication System-64376.png
IN He–Ne laser the most favorable ratio of helium to neon for satisfactory laser action is
  • 1 : 4
  • 4 : 1
  • 1 : 7
  • 7 : 1
For good demodulation of AM signal of carrier frequency f, the value of RC should be

  • Physics-Communication System-64378.png
  • 2)
    Physics-Communication System-64379.png

  • Physics-Communication System-64380.png

  • Physics-Communication System-64381.png
Of the following which is preferred modulation scheme for digital communication
  • Pulse Code Modulation (PCM)
  • Pulse Amplitude Modulation (PAM)
  • Pulse Position Modulation (PPM)
  • Pulse Width Modulation (PWM)
The SKIP ZONE in Radio Wave Transmission is that range where
  • There is no reception of either ground wave or sky wave
  • The reception of ground wave is maximum but that of sky wave is minimum
  • The reception of ground wave is minimum, but that of sky wave is maximum
  • The reception of both ground and sky wave is maximum
The area of the region covered by the TV broadcast by a TV tower of 100 m height is (radius of the earth = 6.4 × 106m)
  • 12.8π × 108 km2
  • 1.28π × 103 km2
  • 0.64π × 103 km2
  • 1.28 × 103 km2
The velocity of all radio waves in free space is 3 × 108 m/s. The frequency of a radio wave of wavelength 150 m is
  • 20 kHz
  • 2 kHz
  • 2 MHz
  • 1 MHz
The sky wave propagation is suitable for radio-waves of frequency
  • Upto 2 MHz
  • From 2 MHz to 20 MHz
  • From 2 MHz to 30 MHz
  • From 2 MHz to 50 MHz
Modulation is the process of superposing
  • Low frequency audio signal on high frequency waves
  • Low frequency radio signal on low frequency audio waves
  • High frequency audio signal on low frequency radio waves
  • Low frequency audio signal on low frequency radio waves
A transmitting antenna of height h and the receiving antenna of height 45 m are separated by a distance of 40 km for satisfactory communication in line of sight mode. Then the value of h is (given radius of earth is 6400 km)
  • 15 m
  • 20 m
  • 30 m
  • 25 m
  • 40 m
A 1000 kHz carrier wave is modulated by an audio signal of frequency range 100-5000 Hz. Then the width of the channel in kHz is
  • 10
  • 20
  • 30
  • 40
  • 45
The modulation in which pulse duration varies in accordance with the modulating signal is called
  • PAM
  • PPM
  • PWM
  • PCM
  • PFM
Which of the following frequencies will be suitable for beyond the horizon communication
  • 10 kHz
  • 10 MHz
  • 1 GHz
  • 1000 GHz
If both the length of an antenna and the wavelength of the signal to be transmitted are doubled, the power radiated by the antenna
  • Is doubled
  • Is halved
  • Remains constant
  • Is quadrupled
  • Increases 16 times
If the maximum amplitude of an amplitude modulated wave is 25 V and the minimum amplitude is 5 V, the modulation index is
  • 1/5
  • 1/3
  • 3/2
  • 2/5
  • 2/3
A modem is a
  • Modulating device only
  • Demodulating device only
  • Modulating and demodulating device
  • Transmitting device
  • Receiving device
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