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NCERT Solutions for class 12 Physics | Chapter 15 - Communication Systems

(1) Which of the following is not transducer?
[A] Loudspeaker
[B] Amplifier
[C] Microphone
[D] All
Answer: Amplifier
(2) The length of a half wave dipole at 30 mega-hertz is:
[A] 5 m
[B] 10 m
[C] 25 m
[D] 80 m
Answer: 5 m

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(3) Name the man who was first to place his foot on the moon and in which year:
[A] Neil Armstrong, 1969
[B] James Van A lien, 1971
[C] Leonov, 1965
[D] None of these
Answer: Neil Armstrong, 1969
(4) A loudspeaker converts:
[A] electrical signals into sound signals
[B] sound signals into electrical signals
[C] both (a) and (b)
[D] neither (a) nor (b)
Answer: electrical signals into sound signals
(5) In space communication, the sound waves can be sent from one place to another:
[A] through space
[B] through wires
[C] by superimposing it on undamped electro-magnetic waves
[D] by superimposing it on damped electro-magnetic waves
Answer: by superimposing it on undamped electro-magnetic waves
(6) A microphone converts:
[A] sound signals into electrical signals
[B] electrical signals into sound signals
[C] both (a) and (b)
[D] Neither (a) nor (b)
Answer: sound signals into electrical signals
(7) The modulation index in amplitude modulation is:
[A] Always zero
[B] Between 0 and 1
[C] Between 1 and ∞
[D] None of these
Answer: Between 1 and ∞
(8) The space waves which are affected seriously by atmospheric conditions are:
[A] MF
[B] HUF
[C] VHF
[D] UHF
Answer: UHF
(9) The area served by an antenna of height 100 m is:
[A] 109
[B] 4 × 109 m²
[C] 6 × 109
[D] 8 × 1010
Answer: 4 × 109 m²
(10) Broadcasting antenna are generally:
[A] Ommi directional type
[B] Vertical type
[C] Horizontal type
[D] None
Answer: Vertical type
(11) The audio frequencies range from:
[A] 20 Hz to 20.000 kHz
[B] 20 Hz to 20 kHz
[C] 20 kHz to 20.000 kHz
[D] None of these
Answer: 20 Hz to 20 kHz
(12) Who undertook the first space walk and in which year?
[A] Leonov 1965
[B] Neil Armstrong, 1969
[C] Rakesh Sharma. 1998
[D] None of these
Answer: Leonov 1965
(13) An antenna is:
[A] Inductive
[B] Capacitive
[C] Resistive
[D] A transformer
Answer: Inductive
(14) The sound produced by a tuning fork is a sort of:
[A] analog signal
[B] digital signal
[C] both (a) and (b)
[D] neither (a) nor (b)
Answer: analog signal
(15) The wavelength of a wave of frequency 10 kHz is:
[A] 30 m
[B] 300 m
[C] 30 km
[D] 300 km
Answer: 30 km
(16) The term used “to collect the information about an object and a place without physical contact” is called :
[A] modulation
[B] communication
[C] amplification
[D] remote sensing
Answer: remote sensing
(17) The velocity of electromagnetic wave is:
[A] 3 × 105 ms-1
[B] 3 × 106 ms-1
[C] 3 × 108 ms-1
[D] 3 × 1010 ms-1
Answer: 3 × 108 ms-1
(18) The output of a digital computer is an example of:
[A] digital signal
[B] analog signal
[C] both (a) and (b)
[D] neither (a) nor (b)
Answer: digital signal
(19) The output of a digital computer is an example of:
[A] digital signal
[B] analog signal
[C] both (a) and (b) above
[D] neither (a) nor (b)
Answer: digital signal
(20) AM is used for broadcasting because:
[A] it is more noise immune than other modulation system
[B] it requires less transmitting power compare with other systems
[C] its use avoids receiver complexity
[D] No other modulation system can provide the necessary bandwidth faithful transmission
Answer: its use avoids receiver complexity

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