## Communication System Quiz-3

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.

Q21. Which of the following explain that all galaxies are receding from us?
•  White dwarfs
•  Neutron stars
•  Black holes
•  Red shift
Solution
Hubble’s law is the statement in physical cosmology that the red shift in light coming from distant galaxies is proportional to their distance V=H0D
Where V is the recessional velocity due o red shift, H0 is Hubble’s constant, D is the proper distance that the light had travelled from the galaxy in the res frame of the observer. This effect helps us in explaining the fact that galaxies are receding from us.

Q22.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
Solution
The surface of earth is curved like a sphere

Q23.  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
Solution

Q24. An optical fiber made of glass with a core of refractive index of 1.55 and include with another glass with a refractive index of 1.51. Launching takes place from air. What is the value of critical angle for core-clad boundary?
•  65°
•  72°
•  77°
•  82°
Solution

Q25.In satellite communication, the communication satellite;
•  Acts as a reflector for a beam of modulated microwave from transmitter sent directly towards it
•  Acts as a repeater for a signal reaching there, without any change in frequency
•  Receives the coming modulated microwave signal, amplifies it and returns it to earth at a              different frequency
•  None of the above
Solution
A communication satellite receives the coming modulated microwave signal, amplifies it and return it to earth at a different frequency

Q26. The modulation index of a FM signal is 0.25. If modulating frequency is 2kHz, the maximum derivative in frequency would be
•  500 Hz
•  1000 Hz
• 1500 Hz
•  500 kHz
Solution

Q27.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 the above
Solution
Frequency modulation

Q28.The resistance of copper wire of diameter=2 mm is of the order of
Solution

Q29.The galaxy in which we live is
•  Milkyway
•  Spiral galaxy
•  None of the above
Solution
Milkway is a glowing belt in sky formed due to the combined light of the large number of stars constituting it. Our solar system is part of Milkway

Q30. If Ec=20sin105Ï€t and Em=10sin⁡400 Ï€t are carrier and modulating signals respectively, he modulation index is
•  56 %
•  30 %
•  50 %
• 40 %
Solution
m=Em/Ec =50%

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