We have compiled the NCERT MCQ Questions for Class 12 Physics Chapter 15 Communication Systems with Answers Pdf free download covering the entire syllabus. Practice MCQ Questions for Class 12 Physics with Answers on a daily basis and score well in exams. Refer to the Communication Systems Class 12 MCQs Questions with Answers here along with a detailed explanation.
Communication Systems Class 12 MCQs Questions with Answers
Question 1.
Modulation index of an AM signal:
(a) depends upon the peak amplitude of the modulating signal and the carrier.
(b) depends upon the peak amplitude of modulating signal.
(c) is a function of carrier frequency.
(d) None of these.
Answer
Answer: (a) depends upon the peak amplitude of the modulating signal and the carrier.
Question 2.
In amplitude modulation
(a) the amplitude of the carrier remains constant.
(b) the amplitude of the carrier varies in accordance with the amplitude of the modulating signal.
(c) the amplitude of carrier varies in accordance with the frequency of the modulating signal.
(d) None of these.
Answer
Answer: (b) the amplitude of the carrier varies in accordance with the amplitude of the modulating signal.
Question 3.
In modulation process, radio frequency wave is termed as
(a) modulating wave
(b) modulated wave
(c) carrier wave
(d) none
Answer
Answer: (c) carrier wave
Question 4.
Digital signals:
(a) represent values as discrete steps.
(b) utilise binary code system.
(c) do not provide a continuous set of values.
(d) All of these.
Answer
Answer: (d) All of these.
Question 5.
Modulation index in an FM signal:
(a) Varies directly as the modulating frequency.
(b) Varies directly as frequency deviation and inversely as the modulating frequency.
(c) varies inversely as the frequency deviation. ‘
(d) None of these.
Answer
Answer: (b) Varies directly as frequency deviation and inversely as the modulating frequency.
Question 6.
The most commonly employed analog modulation technique in satellite communication is the
(a) amplitude modulation
(b) frequency modulation
(c) phase modulation
(d) All of the above.
Answer
Answer: (b) frequency modulation
Question 7.
Satellite transponders
(a) use a high frequency for reception and a lower frequency for retransmission of information to and from earth
(b) use a lower frequency for reception and a higher frequency for retransmission of information to and from earth.
(c) Use a single frequency for reception and retransmission of information to and from earth.
(d) none of the above.
Answer
Answer: (a) use a high frequency for reception and a lower frequency for retransmission of information to and from earth
Question 8.
For television transmission, the frequency employed is normally in the range
(a) 30-300 Hz
(b) 30-300 kHz
(c) 30-300 MHz
(d) 30-300 GHz.
Answer
Answer: (c) 30-300 MHz
Question 9.
Which one of the following can happen to the electromagnetic waves travelling in free space:
(a) Reflection
(b) Refraction
(c) absorption
(d) attenuation
Answer
Answer: (d) attenuation
Question 10.
High frequency waves are
(a) reflected by E layer.
(b) absorbed by F layer.
(c) affected by the solar cycle.
(d) capable of use for long-distance transmission.
Answer
Answer: (a) and (c).
Question 11.
Which of the following is invariably found on all communication satellites as a payload
(a) transponder
(b) photographic camera
(c) optical telescope
(d) None of these
Answer
Answer: (a) transponder
Question 12.
An antenna is
(a) capacitive
(b) reactive
(c) inductive above its resonance frequency.
(d) None of these
Answer
Answer: (c) inductive above its resonance frequency.
Question 13.
Microwave link repeaters are typically 50 km apart,
(a) because of atmospheric attenuation.
(b) because of the earth’s curvature.
(c) to ensure that signal voltage may not harm the repeater.
(d) None of these.
Answer
Answer: (b) because of the earth’s curvature.
Question 14.
Optical communication uses the frequency range of
(a) 109 to 1010 Hz
(b) 105 to 106 Hz
(c) 1014 to 1015 Hz
(d) 1016 to 1017 Hz.
Answer
Answer: (c) 1014 to 1015 Hz
Question 15.
Audio signals have frequency range.
(a) 20 Hz to 20 kHz
(b) 20 kHz to 20 MHz
(c) 20 MHz to 20 GHz
(d) All of these.
Answer
Answer: (a) 20 Hz to 20 kHz
Question 16.
The numbers of geostationary satellites needed for uninterrupted global coverage is
(a) 3
(b) 4
(c) 2
(d) 1
Answer
Answer: (a) 3
Question 17.
The maximum distance upto which T.V. signals can be received from an antenna of height h is
(a) \(\sqrt{2hr}\)
(b) h\(\sqrt{2R}\)
(c) R\(\sqrt{2h}\)
(d) None of these.
Answer
Answer: (a) \(\sqrt{2hr}\)
Question 18.
The information bearing signal is called
(a) Base band signal
(b) digital signal
(c) Analog signal
(d) None of these
Answer
Answer: (a) Base band signal
Question 19.
In a single reflection from the ionosphere, the sky waves cover a distance on ground not more than
(a) 400 m
(b) 4,000 m
(c) 400 km
(d) 4,000 km
Answer
Answer: (d) 4,000 km
Question 20.
AM is used for broadcasting because
(a) it is more noise immune than other modulation systems.
(b) it requires less transmitting power compared with other systems.
(c) its use avoids receiver complexity.
(d) no other modulation system can provide the necessary band width faithful transmission.
Answer
Answer: (c) its use avoids receiver complexity.
Fill in the Blanks
Question 1.
………………. is a device which converts energy from one form to another.
Answer
Answer: Transducer.
Question 2.
………………. separates out the audio signal from the modulated signal.
Answer
Answer: Demodulator.
Question 3.
Marconi antenna has length ………………. while Hertz antenna has a length equal to ……………….
Answer
Answer: \(\frac {λ}{4}\), \(\frac {λ}{2}\)
Question 4.
The length of antenna required to transmit a radio signal of frequency 1 MHz is about ……………….
Answer
Answer: 75 m.
Question 5.
The bandwidth of a complex audio signal is equal to ………………. of the audio signal.
Answer
Answer: Twice the maximum frequency.
Question 6.
In-frequency modulated signal the informatibn is contained in the ………………. and the bandwidth is ……………….
Answer
Answer: side bands, 2n × frequency of modulating signal where n is the number of significant side band pairs.
Question 7.
To achieve pulse code modulation an analog signal is ………………., ………………. and then coded.
Answer
Answer: sampled, quantised.
Question 8.
A digital signal is described by the ……………….
Answer
Answer: bit rate i.e., number of binary digits (bits) per second.
Question 9.
The electromagnetic waves of radio frequencies are reflected by ………………. and this effect is used for round the curved surface of earth.
Answer
Answer: Ionosphere, transmission of radio signals.
Question 10.
The bandwidth for AM radio station is ………………. and for an FM radio station, the bandwidth is ……………….
Answer
Answer: 10 kHz, 150 kHz.
Question 11.
The modulation index of an AM wave lies between ……………….
Answer
Answer: 0 and 1.
Question 12.
The rate at which a modem can transmit and receive data is expressed as ……………….
Answer
Answer: BPS (bits per second).
Question 13
………………. is preferred for high fidelity reception.
Answer
Answer: Frequency modulation.
Question 14.
Bit rate = ………………. × number of bits per sample.
Answer
Answer: Sampling rate.
Question 15
………………. are the relevant waves in telecommunication.
Answer
Answer: Microwaves.
Question 16.
We use short wave bands only for long distance radio broadcast because ……………….
Answer
Answer: Ionosphere easily reflects the waves in this band.
Question 17
………………. uses carrier signals having frequencies in the range 1012 Hz to 1016 Hz.
Answer
Answer: Optical communication.
Question 18.
The electromagnetic wave of frequency 120 MHz belongs to ……………….
Answer
Answer: Frequency modulated band.
Question 19.
The essential condition for demodulation is that the time period of high frequency carrier wave must be ……………….
Answer
Answer:
much smaller than the time constant of RC circuit i.e.,
Tc < < τ
\(\frac {1}{f_c}\) << RC
Question 20.
In amplitude modulation, the modulation index or degree of modulation is the ratio of ……………….
Answer
Answer:
amplitude of modulating signal to the amplitude of carrier wave.
m = \(\frac {E_m}{E_c}\) = \(\frac {V_m}{V_c}\)
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