JEE Questions for Physics Communication System Quiz 7 - MCQExams.com

What is the modulation index of an over modulated wave?
  • 1
  • Zero
  • < 1
  • > 1
Basically, the product modulator is
  • An amplifier
  • A mixer
  • A frequency separator
  • A phase separator
If fa and ff represent the carrier wave frequencies for amplitude and frequency modulations respectively, then
  • fa > ff
  • fa < ff
  • fa = ff
  • fa ≥ ff
Which of the following is the disadvantage of FM over AM?
  • Larger band width requirement
  • Large 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-64253.png

  • Physics-Communication System-64254.png
  • None of the above
An AM wave has 1800 watt of total power content. For 100% modulation the carrier should have power content equal to
  • 1000 watt
  • 1200 watt
  • 1500 watt
  • 1600 watt
The frequency of a FM transmitter without signal input is called
  • Lower side band frequency
  • Upper side band frequency
  • Resting frequency
  • None of the above
What type of modulation is employed in India for radio transmission?
  • Amplitude modulatio
  • Frequency modulation
  • Pulse modulation
  • None of these
When the modulating frequency is doubled, the modulation index is halved and the modulating voltage remains constant, the modulation system is
  • Amplitude modulation
  • Phase modulation
  • Frequency modulation
  • All of these
An antenna is a device
  • That converts electromagnetic energy into radio frequency signal
  • That converts radio frequency signal into electromagnetic energy
  • That converts guided electromagnetic waves into free space electromagnetic waves and vice-versa
  • None of the above
While tunning 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
In a communication system, noise is most likely to affect the signal
  • At the transmitter
  • In the channel or in the transmission line
  • In the information source
  • At the receiver
In a 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
Consider telecommunication through optical fibres. Which of the following statements is not true?
  • Optical fibres may have homogeneous core with a suitable cladding
  • Optical fibres can be of graded refractive index
  • Optical fibres are subject to electromagnetic interference from outside
  • Optical fibres have extremely low transmission loss
The phenomenon by which light travels in an optical fibres is
  • Reflection
  • Refraction
  • Total internal reflection
  • Transmission
Television signals on earth cannot be received at distances greater than 100 km from the transmission station. The reason behind this is that
  • The receiver antenna is unable to detect the signal at a distance greater than 100 km
  • The TV programme consists of both audio and video signals
  • The TV signals are less powerful than radio signals
  • The surface of earth is curved like a sphere
Advantage of optical fibre
  • High bandwidth and EM interference
  • Low bandwidth and EM interference
  • High bandwidth, low transmission capacity and no EM interference
  • High bandwidth, high data transmission capacity and no EM interference
In ruby laser, the stimulated emission is due to transition from
  • Metastable state to any lower state
  • Any higher state to lower state
  • Metastable state to ground state
  • Any higher state to ground state
The fundamental radio antenna is a metal rod which has a length equal to
  • λ, in free space at the frequency of operation
  • λ / 2 in free space at the frequency of operation
  • λ / 4 in free space at the frequency of operation
  • 3 λ /4 in free space at the frequency of operation
When a low flying aircraft passes over head, we sometimes notice a slight shaking of the picture on our TV screen. This is due to
  • Diffraction of the signal received from the antenna
  • Interference of the direct signal received by the antenna with the weak signal reflected by the passing aircraft
  • Change of magnetic flux occurring due to the passage of aircraft
  • Vibrations created by the passage of aircraft
When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is
  • 0 rad
  • (3π/rad
  • (π /rad
  • π rad
Which of the following device is fully duplex?
  • Mobile phone
  • Walky-talky
  • Loud speaker
  • Radio
The principle of LASER action involves
  • Amplification of particular frequency emitted by the system
  • Population inversion
  • Stimulated emission
  • All of the above
The wavelength of red light from He-Ne laser is 633 nm in air but 474 nm in the aqueous humor inside the eye ball. Then the speed of red light through the aqueous humor is

  • Physics-Communication System-64257.png
  • 2)
    Physics-Communication System-64258.png

  • Physics-Communication System-64259.png

  • Physics-Communication System-64260.png

  • Physics-Communication System-64261.png
In satellite communication
1. The frequency used lies between 5 MHz and 10 MHz
2. The uplink and downlink frequencies are different
3. The orbit of geostationary satellite lies in the equatorial plane at an inclination of 0°
In the above statements
  • Only 2 and 3 true
  • All are true
  • Only 2 true
  • Only 1 and 2 true
  • Only 1 and 3 true
A signal wave of frequency 12 kHz is modulated with a carrier wave of frequency 2.51 MHz. The upper and lower side band frequencies are respectively
  • 2512 kHz and 2508 kHz
  • 2522 kHz and 2488 kHz
  • 2502 kHz and 2498 kHz
  • 2522 kHz and 2498 kHz
  • 2512 kHz and 2488 kHz
A radio station has two channels. One is AM at 1020 kHz and the other FM at 89.5 MHz. For good results you will use
  • Longer antenna for the AM channel and shorter for the FM
  • Shorter antenna for the AM channel and longer for the FM
  • Same length antenna will work for both
  • Information given is not enough to say which one to use for which
A diode AM detector with the output circuit consisting of R = 1 kΩ and C =1µF would be more suitable for detecting a carrier signal of
  • 0.1 kHz
  • 0.5 kHz
  • 1 kHz
  • 0.75 kHz
  • 10 kHz
In optical communication system operating at 1200 nm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can be transmitted is
  • 2 million
  • 10 million
  • 0.1 million
  • 1 million
  • 0.5 million
A carrier frequency of 1 MHz and peak value of 10V is amplitude modulated with a signal frequency of 10 kHz with peak value 0.5 V. Then the modulation index and the side band frequencies respectively are
  • 0.05 and 1 ± 0.010 MHz
  • 0.5 and 1 ± 0.010 MHz
  • 0.05 and 1 ± 0.005 MHz
  • 0.5 and 1 ± 0.005 MHz
  • 0.05 and 1 ± 0.100 MHz
0:0:1


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