## COMMUNICATION SYSTEM Quiz-19

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. .

Q1. The area of the region covered by the TV broadcast by a TV tower of 100 m height is (radius of the earth =6.4×106 m)
•  12.8Ï€×108 km2
•  1.28Ï€×103 km2
•  0.64Ï€×103 km2
•  1.28Ï€×103 km2
Solution
Area covered by T.V. signals A=2Ï€hR=2×3.14×100×6.4×106=128Ï€×108 ⇒A=1.28Ï€×103 km2

Q2.The sky wave propagation is suitable for radio-waves of frequency
•  Upto 2 MHz
•  From 2 MHz to 20 MHz
•  From 2 MHz to 30 MHz
•  From 2 MHz to 50 MHz
Solution
The sky waves are the radiowaves of frequency between 2 MHz to 30 MHz. These waves can propagate through atmosphere but reflected back by the ionosphere of earth’s atmosphere. These waves can propagate from transmitter to receiver through sky, therefore, their propagation is called sky wave propagation.

Q3. The special theory of relativity is based on the frame of reference which has constant?
•   Acceleration
•  Speed
•  Time interval
•  Space interval
Solution
The special theory of relativity is based on the frame of reference which moves with constant speed

Q4. Through which mode of propagation, the radio waves can be sent from one place to another
•  Ground wave propagation
•  Sky wave propagation
•  Space wave propagation
•  All of the above
Solution
The radio waves can be sent from one place to another through following propagation mode. (i) space wave propagation, sky wave propagation and ground wave propagation

Q5.Optical fiber communication is generally preferred over general communication system because
•  It is more efficient
•  It has signal security
•  It can be jammed as easily as radiowaves
•  All of the above
Solution
An optical fibre is move efficient, has signal security and cannnot be grounded as easily as radiowaves

Q6. In space communication, the sound waves can be sent from one place to another
•  Through space
•  Through wires
•  By superimposing it on undamped electromagnetic waves
•  By superimposing it on damped electromagnetic waves
Solution
In space communication, the sound waves can be sent from one place to another by superimposing it on undamped electromagnetic waves

Q7.A TV tower has a height of 150 m. The area of the region covered, the TV broadcast is (radius of earth=6.4×106m)
•  9.6Ï€×108 km2
•  19.2Ï€×108 km2
•  19.2Ï€×107 km2
•  1.92Ï€×103 km2
Solution
Area of region covered =Ï€d2=Ï€(2hR) =Ï€×2×150×6.4×106 =1.92 Ï€×109 m2=1.92 Ï€×103 km2

Q8.The maximum line-of-sight distance dM between two antennas having heights hT and hR above the earth is
•  √(R(hT+hR)
•  √(2R(hT+hR)
•  √RhT +√2RhR
•  √2RhT +√2RhR
Solution
√(2RhT )+√(2RhR )

Q9.For sky wave propagation of 10 MHz signal, what should be the minimum electron density in ionosphere?
•  ~ 1.2 ×1012 m-3
•  ~ 106 m-3
•  ~ 1014 m-3
•  ~ 1022 m-3
Solution
Area (A) covered by TV signal is given by A=Ï€d2 Where d is range given by d=√2Rh Where Ris radius of earth and h the height of antenna. ∴A=Ï€(2Rh) Given, A1=A,A2=2A ∴A1/A2 =h1/h2 ⇒ h1/h2 =1/2 ⇒h2=2h1 Hence, height of transmitting antenna will have to be doubled.

Q10. In frequency modulation
•  The amplitude of modulated wave varies as frequency of carrier wave
•  The frequency of modulated wave varies as amplitude of modulating wave
•  The frequency of modulated wave varies as frequency of modulating wave
•  The frequency of modulated wave varies as frequency of carrier wave
Solution
In frequency modulation the frequency of the modulated wave is the linear function of the amplitude of the modulating wave

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