## Communication System Quiz-6

As per analysis for previous years, it has been observed that students preparing for NEET find Physics out of all the sections to be complex to handle and the majority of them are not able to comprehend the reason behind it. This problem arises especially because these aspirants appearing for the examination are more inclined to have a keen interest in Biology due to their medical background.

Furthermore, sections such as Physics are dominantly based on theories, laws, numerical in comparison to a section of Biology which is more of fact-based, life sciences, and includes substantial explanations. By using the table given below, you easily and directly access to the topics and respective links of MCQs. Moreover, to make learning smooth and efficient, all the questions come with their supportive solutions to make utilization of time even more productive. Students will be covered for all their studies as the topics are available from basics to even the most advanced.

Q51. A given fiber has core refractive index of 1.5 and a core cladding index difference factor (∆) of 0.01125. The numerical aperture is
•  0.252
•  0.225
•  0.5
•  2.25
Solution

Q52.A carrier is simultaneously modulated by two sine waves having modulation indices of 0.3 and 0.4. The total modulation index will be
•  0.1
•  0.5
•  0.7
•  0.35
Solution

Q53.  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
•  15
•  20
•  30
•  25
Solution

Q54. What is the minimum length of antenna required to transmit a radio signal of frequency 20 MHz?
•  5.0 m
•  7.5 m
•  2.0 m
•  3.75 m
Solution
Given, the frequency of radio signal v=20 MHz=20×106 Hz The wavelength of the antenna is Î»=c/v Î»=(3×108)/(20×106) or Î»=15 m ∴ For efficient radiation and reception, the height of transmitting and receiving antennas should be comparable to a quarter wavelength of the frequency used. ∵ The minimum length of antenna =Î»/4=15/4=3.75 m

Q55.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
•  Different 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
Solution
Interference of the direct signal received by the antenna with the weak signal reflected by the passing   aircraft

Q56. What should be minimum length of antenna for efficient transmission of signals of wavelength Î»?
•  Î»/2
• Î»/3
•  Î»/4
•  Î»/5
Solution
For efficient transmission of signals of wavelength’s Î», the minimum length of antenna should be Î»/4.

Q57.A laser is a coherent source it contains
•  Many wavelength
•  Uncoordinated waves of particular wavelength
•  Coordinated waves of many wavelength
•  Coordinated waves of particular wavelength
Solution
Laser is a coherent source of coordinated waves of particular wavelength

Q58.Primary constant of a transmission line are
•  Resistance and inductance
•  Capacitance and conductance
•  Both (a) and (b)
•  None of the above
Solution
A transmission line has four primary constants, resistance, inductance, capacitance and conductance

Q59.The glass of optical fiber has refractive index 1.55 and is clad with another glass of refractive index 1.51. When the surrounding is air, the numerical aperture will be
•  0.625
•  0.350
•  0.528
•  0.704
Solution

Q60. In frequency modulated wave
•  Frequency varies with time
•  Amplitude varies with time
•  Both frequency and amplitude vary with time
• Both frequency and amplitude are constant
Solution
In frequency modulation, frequency of carrier signal varies in accordance with the modulating signal. The amplitude of the carrier wave is fixed while its frequency is changing. When the instantaneous amplitude of the modulating voltage is large, the instantaneous carrier frequency is higher. It is lower when the modulation voltage is small.

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