Class 12 Communication Systems CBSE Questions & Answers

Class 12 · Communication Systems

This is Physics Class 12 Communication Systems CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
need for modulation also arises from
  • A
    need to transmit a number of signals simultaneously on the same transmitter
    Correct
  • B
    to transmit 10 different signals at the same time we need 100 transmitters
  • C
    need to transmit same signal twice or thrice
  • D
    to transmit 10 different signals at the same time we need 20 transmitters
2
Given that a sinusoidal carrier is given by \(c\left( t \right) = {A_c}\sin \left( {{\omega _c} + \emptyset } \right)\), in amplitude modulation the quantity depends on baseband signal is
  • A
    none of these
  • B
    \({\omega _c}\)
  • C
    \(\emptyset \)
  • D
    \({A_c}\)
    Correct
3
Given that a sinusoidal carrier is given by \(c\left( t \right) = {A_c}\sin \left( {{\omega _c} + \emptyset } \right)\), in frequency modulation the quantity depends on baseband signal is
  • A
    \(\emptyset \)
  • B
    \({A_c}\)
  • C
    none of these
  • D
    \({\omega _c}\)
    Correct
4
Given that a sinusoidal carrier is given by \(c\left( t \right) = {A_c}\sin \left( {{\omega _c} + \emptyset } \right)\), in phase modulation the quantity depends on baseband signal is
  • A
    \({\omega _c}\)
  • B
    \({A_c}\)
  • C
    \(\emptyset \)
    Correct
  • D
    none of these
5
Pulse is specified by pulse height or the peak voltage, the pulse duration and pulse to pulse spacing. In pulse amplitude modulation (PAM) what changes with base band signal is
  • A
    pulse duration
  • B
    none of these
  • C
    pulse height or the peak voltage
    Correct
  • D
    pulse to pulse spacing
6
A special case of amplitude modulation is where the baseband signal is a pure sine wave. If \({\omega _c}\) is the carrier frequency and \({\omega _m}\) the base band signal, the spectrum of the modulated signal contains
  • A
    4 discrete values
  • B
    3 discrete values
    Correct
  • C
    5 discrete values
  • D
    2 discrete values
7
A special case of amplitude modulation is where the baseband signal is a pure sine wave. If \({\omega _c}\) is the carrier frequency and \({\omega _m}\) the base band signal, the spectrum of the modulated signal contains the values
  • A
    \({\omega _c}\), \({\omega _c}\)+ \({\omega _m}\) , \({\omega _c}\) -\(2{\omega _m}\)
  • B
    \({\omega _c}\), \({\omega _c}\)+ \(2{\omega _m}\) , \({\omega _c}\) -\({\omega _m}\)
  • C
    \(2{\omega _c}\), \({\omega _c}\)+ \({\omega _m}\) , \({\omega _c}\) -\({\omega _m}\)
  • D
    \({\omega _c}\), \({\omega _c}\) + \({\omega _m}\) , \({\omega _c}\) -\({\omega _m}\)
    Correct
8
If AC and AM are the amplitudes of the carrier and baseband signals then modulation index in amplitude modulation is
  • A
    \({{\rm{A}}_{\rm{M}}}/{\rm{ }}{{\rm{A}}_{\rm{C}}}\)
    Correct
  • B
    \({{\rm{A}}_{\rm{M}}}/{\rm{ 2}}{{\rm{A}}_{\rm{C}}}\)
  • C
    \({{\rm{A}}_{\rm{C}}}/{\rm{ }}{{\rm{A}}_{\rm{M}}}\)
  • D
    \({{\rm{A}}_{\rm{C}}}/{\rm{ 2}}{{\rm{A}}_{\rm{M}}}\)
9
To reduce the distortion in amplitude modulation, modulation index is kept
  • A
    small
    Correct
  • B
    very large
  • C
    equal to 1
  • D
    large
10
A message signal of frequency 10 kHz and peak voltage of 10 volts is used to modulate a carrier of frequency 1 MHz and peak Voltage of 20 volts. Determine the modulation index
  • A
    2
  • B
    0.25
  • C
    1
  • D
    0.5
    Correct
11
A message signal of frequency 10 kHz and peak voltage of 10 volts is used to modulate a carrier of frequency 1 MHz and peak voltage of 20 volts. Determine the side bands produced.
  • A
    1030 kHz and 990 kHz
  • B
    1020 kHz and 960 kHz
  • C
    1010 kHz and 990 kHz
    Correct
  • D
    1020 kHz and 980 kHz
12
One method of producing an amplitude modulation is to add the carrier and modulating signal and then
  • A
    a square law device followed by a high pass filter
  • B
    a cubic law device followed by a high pass filter
  • C
    a square law device followed by a low pass filter
    Correct
  • D
    a cubic law device followed by a low pass filter
13
Before transmission the AM produced by a square law device
  • A
    goes through a transconductance amplifier
  • B
    goes through a power amplifier
    Correct
  • C
    goes through a current amplifier
  • D
    goes through a voltage amplifier
14
The range of an AM broadcast depends
  • A
    carrier frequency only
  • B
    antenna power and carrier frequency
    Correct
  • C
    antenna power only
  • D
    none of these
15
AM produced by a square law device is passed through a power amplifier and fed to
  • A
    repeater
  • B
    antenna
    Correct
  • C
    none of these
  • D
    receiver