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
AM detection is
  • A
    recovering the modulating signal from the received signal
    Correct
  • B
    finding the type of modulation
  • C
    none of these
  • D
    detecting whether it is modulated
2
A rectifier and an envelope detector for AM uses
  • A
    transistors for rectification and zener diodes for storing the peaks
  • B
    none of these
  • C
    diodes for rectification and capacitors for storing the peaks
    Correct
  • D
    opamps for rectification and zener diodes for storing the peaks
3
Which of the following frequencies will be suitable for beyond-the horizon communication using sky waves?
  • A
    1000 GHz
  • B
    10 kHz
  • C
    1 GHz
  • D
    10 MHz
    Correct
4
Frequencies in the UHF range normally propagate by means of:
  • A
    Ground waves.
  • B
    Sky waves
  • C
    Space waves
    Correct
  • D
    Surface waves.
5
Digital signals, (i) do not provide a continuous set of values, (ii) represent values as discrete steps, (iii) can utilize binary system, and (iv) can utilize decimal as well as binary systems. Which of the above statements are true?
  • A
    (i) and (ii) only
  • B
    All of (i), (ii), (iii) and (iv).
  • C
    (i), (ii) and (iii) but not (iv)
    Correct
  • D
    (ii) and (iii) only
6
Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line-of-sight communication? A TV transmitting antenna is 81m tall. How much service area can it cover if the receiving antenna is at the ground level?
  • A
    No, 3345 \({\rm{k}}{{\rm{m}}^{\rm{2}}}\)
  • B
    No, 3258 \({\rm{k}}{{\rm{m}}^{\rm{2}}}\)
    Correct
  • C
    yes, 3000 \({\rm{k}}{{\rm{m}}^{\rm{2}}}\)
  • D
    No, 3000 \({\rm{k}}{{\rm{m}}^{\rm{2}}}\)
7
A carrier wave of peak voltage 12V is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of 75\(\% \)?
  • A
    9 V
    Correct
  • B
    7 V
  • C
    6 V
  • D
    8 V
8
Multiplexing is a scheme for transmitting multiple signals at the same time e.g. speeches of ten persons in different rooms on the same channel. How many transmitters will be required in any multiplexing scheme?
  • A
    two
  • B
    three
  • C
    one
    Correct
  • D
    ten
9
In Amplitude modulation if one of the two side bands is removed by a filter is it possible to recover the modulating signal?
  • A
    Yes
    Correct
  • B
    No if the signal is strong
  • C
    Yes if signal is weak
  • D
    No
10
Suppose that on an AM signal, the Maximum peak to peak voltage value read from the graticule on the oscilloscope screen is 5.9 divisions and the Minimum peak to peak voltage value is 1.2 divisions. What is the modulation index?
  • A
    0.562
  • B
    0.762
  • C
    0.462
  • D
    0.662
    Correct
11
A standard AM broadcast station is allowed to transmit modulating frequencies up to 5 kHz. If the AM station is transmitting on a frequency of 980 kHz, maximum and minimum upper and lower sidebands are
  • A
    995 kHz, 985
  • B
    985 kHz, 995
  • C
    985 kHz, 975 kHz
    Correct
  • D
    975 kHz, 975
12
A standard AM broadcast station is allowed to transmit modulating frequencies up to 5 kHz. If the AM station is transmitting on a frequency of 980 kHz, total bandwidth occupied by the AM station is
  • A
    10 kHz
    Correct
  • B
    15 kHz
  • C
    14 kHz
  • D
    12 kHz
13
A formula for computing the total power in an AM signal when the carrier power and the modulation index are known is PT = Pc \(\left( {1 + {{{m^2}} \over 2}} \right)\) . If the carrier of an AM transmitter is 1000 W and it is modulated 100 percent the total AM power is
  • A
    1000 W
  • B
    2000 W
  • C
    500 W
  • D
    1500 W
    Correct
14
A formula for computing the total power in an AM signal when the carrier power and the modulation index are known is \({{\rm{P}}_{\rm{T}}} = {\rm{Pc}}\) \(\left( {1 + {{{m^2}} \over 2}} \right)\) . if the carrier of an AM transmitter has a power = 30 W and it is modulated 85 percent the total AM power is
  • A
    44.8 W
  • B
    42.8 W
  • C
    40.8 W
    Correct
  • D
    46.8 W
15
A formula for computing the total power in an AM signal when the carrier power and the modulation index are known is \({{\rm{P}}_{\rm{T}}} = {\rm{ Pc}}\) \(\left( {1 + {{{m^2}} \over 2}} \right)\) . If the carrier of an AM transmitter has a power = 30 W and it is modulated 85 percent the power in one sideband is
  • A
    7.2 W
  • B
    5.4 W
    Correct
  • C
    8.1 W
  • D
    6.4 W