## Communication System Quiz-7

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.

Q61. Which of the following statements is wrong?
•  Ground wave propagation can be sustained at frequencies 500 kHz to 1500 kHz
•  Satellite communication is useful for the frequencies above 30 MHz
•  Sky wave propagation is useful in the range of 30 to 40 MHz
•  Sky wave propagation takes place through tropospheric space
Solution
In ground wave propagation, radio waves travel along the surface of the earth (following the curvature of earth). Ground wave propagation can be sustained only at low frequencies (~ 500 kHz to 1500 kHz) or for radio broadcast at long wavelengths. Satellite communication is useful for the frequencies above 30 MHz which takes place through tropospheric space. The phenomenon involved in the sky wave propagation is total internal reflection.

Q62.For a body moving with relativistic speed, if the velocity is doubled, then
•  Its linear momentum is doubled
•  Its linear momentum will be less than double
•  Its linear momentum will be more than double
•  Its linear momentum remains unchanged
Solution

•   Ground wave
•  Ionospheric wave
•  Direct wave
•  Sky wave
Solution
Direct wave

Q64. An antenna is a device
•  That convert 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 these
Solution
An antenna is a metallic structure used to radiate or receive EM waves

Q65.In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be
•  50 cycles/s
•  100 cycles/s
•  500 cycles/s
•  50,000 cycles/s
Solution
Carrier frequency > audio frequency

Q66. Range of frequencies allotted for commercial UHF TV broadcast is
•  470-960 kHz
•  47-960 MHz
•  470-960 MHz
•  47-960 kHz
Solution
For commercial UHF, TV broadcasts, the range allotted is 470-960 MHz

Q67.The space wave propagation is utilized in
•  Only television communication
•  Can be reflected by ionosphere
•  Cannot be reflected by mesosphere
•  Cannot be reflected by any layer of earth's atmosphere
Solution
The space wave communication is utilized in all the three communication i.e, television, radar and microwave communication

Q68.What fraction of the surface area of earth can be covered to establish communication by one geostationary satellite?
•  1/2
•  1/3
•  1/4
•  1/8
Solution
We uses three geostationary satellites placed at the vertiex of an equilateral triangle, then the entire earth, can be covered by the communication network each satellite covers 1/3 of the globe.

Q69. The optical fibres have an inner core of refractive index n1 and a cladding of refractive index n2such that
•  n1=n2
•  n1>=n2
•  n1<n2
•  n1>n2
Solution
Optical fibre is made of a thin glass core (diameter 10 to 100Î¼m) surrounded by a glass coating called cladding is protected by a jacket of plastic. The refractive index of the glass used for making core (n1=1.7) is a little more than the refractive index of the glass (n2=1.5) used for making the cladding ie,n1>n2.

Q70. How many photons are emitted by a laser source of 5×10-3 W operating at 632.2 nm in 2s?
•  3.2×1016
•  1.6×1016
•  4×1016
•  None of these
Solution

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