Communication-System-Quiz-8

Communication System Quiz-8

Dear Readers,

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.

Q71. Which of the following is correct?

•  A single geostationary satellite can cover the whole part of the earth for microwave communication
•  At least three geostationary satellites in the same orbit around earths can cover the whole part of the earth for microwave communication
•  The first Indian communication satellite is Apple
•  The satellite communication is not like the line of sight microwave communication

Solution
At least three geostationary satellite in the same orbit around the earth can cover the whole part of the earth for microwave communication

Q72.A carrier frequency of 1MHz and peak value of 10V is amplitude modulated with a signal frequency of 10 kHz with peak value of 0.5 V. Then the modulation index and the side band frequencies respectively are

•  0.05 and 1±0.010 MHz
•  0.5 and 1±0.010 MHz
•  0.05 and 1±0.005 MHz
•  0.5 and 1±0.005 MHz

Solution
Modulation index, μ=A_m/A_c ⇒μ=0.5V/10V=0.05 The side bands frequencies are v_SB=v_c±v_m =1±0.010 MHz

Q73.  When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is

•  0 rad
•  (3π/2) rad
•  (π/2) rad
•  π rad

Solution
0 rad

Q74. In optical communication system operating at 1200 nm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can be transmitted is

•  2 million
•  10 million
•  0.1 million
•  1 million

Solution
                       

Q75.Consider an optical communication system operating at λ~800 nm. Suppose, only 1% of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of 8 kHz

•  4.8×10⁸
•  48
•  6.2×10⁸
•  4.8×10⁵

Solution             

                        

                       

Q76. In satellite communication 1. The frequency used lies between 5 MHz and 10 MHz 2. The uplink and downlink frequencies are different. 3. The orbit of geostationary satellite lies in the equatorial plane at an inclination of 0°. In the above statements

•  Only 2 and 3 are true
•  All are true
•  Only 2 is true
•  Only 1 and 2 are true

Solution
1. The frequency used for satellite communication is greater than 30 MHz.
2. Uplink and downlink frequencies are different to avoid interference.
3. Geostationary satellite lies in the equatorial plane of great circle. It should revolve in an orbit concentric and coplanar with the equatorial plane.

Q77.A 500 Hz modulating voltage fed into an FM generator produces a frequency deviation of 2.25 kHz. If amplitude of the voltage is kept constant but frequency is raised to 6 kHz then the new deviation will be

•  4.5 kHz
•  54 kHz
•  27 kHz
•  15 kHz

Solution
m_f=δ/f_m =2250/500=4.5
∴ New deviation =2(m_ff_m )=2×4.5×6=54 kHz

Q78.Audio signal cannot be transmitted because

• The signal has more noise
•  The signal cannot be amplified for distance communication
•  The transmitting antenna length is very small to design
• The transmitting antenna length is very large and impracticable

Solution
Following are the problems which are faced while transmitting audio signals directly.
(i) These signals are relatively of short range
(ii) If every body started transmitting these low frequency signals directly, mutual interference will render all of them ineffective
(iii) Size of antenna required for their efficient radiation would be larger, i.e., about 75 km

Q79.The maximum electron density in the ionosphere in the morning is 10¹⁰ m^-3. At noon time, it increases to 2×10¹⁰ m^-3.Find the ratio of critical frequency at noon and the critical frequency in the morning.

•  2.00
•  2.82
•  4.00
•  1.414

Solution
                          

Q80. Antenna is

•  Inductive
•  Capacitive
•  Resistive above its resonant frequency
•  Resistive at resonant frequency

Solution
An antenna is a form of tuned circuit consisting of inductance and capacitance, and as a result it has a resonant frequency, at the frequency where the capacitive and inductive reactance’s cancel each other out. At this point the antenna appears purely resistive, the reactance being a combination of the loss resistance and radiation resistance.