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51.	If the highest modulating frequency of the wave is 10 kHz, what is the number of stations that can be accommodated in a bandwidth of 200 kHz?(a) 10(b) 20(c) 5(d) 15I got this question in an interview for job.This intriguing question comes from Communication Systems in section Communication Systems of Physics – Class 12
Answer» CORRECT answer is (a) 10 Best explanation: Number of stations = \(\FRAC {Total \, bandwidth}{(Bandwidth \TIMES STATION)}\). Number of stations = \(\frac {200}{(2 \times 10)}\) Number of stations = 10

52.	What is the maximum distance upto which the TV transmission can be received, if the TV tower has a height of 220 m?(a) 37.75 km(b) 20 km(c) 59.3 km(d) 40.55 kmThis question was posed to me in an interview for job.I'd like to ask this question from Communication Systems topic in division Communication Systems of Physics – Class 12
Answer» RIGHT CHOICE is (c) 59.3 KM Easy explanation: d = √2Rh. d = √2 × 220 × 8 × 10^6 d = 59329.58m ≈ 59330 m d = 59.3 km.

53.	Identify the layer where ozone is present.(a) Troposphere(b) Stratosphere(c) Ionosphere(d) MesosphereI have been asked this question in exam.I would like to ask this question from Communication Systems topic in portion Communication Systems of Physics – Class 12
Answer» The correct answer is (b) STRATOSPHERE Explanation: The OZONE layer is present in the stratosphere. The ozone layer BLOCKS the harmful ultraviolet radiation from reaching us. For this ultraviolet radiation, the wavelength is considered to be3 × 10^-7 m.

54.	Identify the limitation of amplitude modification.(a) The quality of the audio signal is high(b) Amplitude modulation suffers from noise(c) The efficiency of AM transmission is high(d) It does not require a wider channelThe question was posed to me during an online interview.This intriguing question originated from Communication Systems topic in section Communication Systems of Physics – Class 12
Answer» The correct answer is (b) Amplitude MODULATION suffers from noise Explanation: Amplitude modification suffers from noise, the quality of the audio signal is poor, and ALSO the EFFICIENCY of the amplitude modification transmission is low. The other STATEMENTS are not valid.

55.	Find the true statement.(a) The value of the harmonic is equal to its contribution to the waveform(b) The value of the harmonic is directly proportional to its contribution to the waveform(c) The value of the harmonic is independent of its contribution to the waveform(d) The value of the harmonic is inversely proportional to its contribution to the waveformI had been asked this question by my school principal while I was bunking the class.My question is from Communication Systems topic in portion Communication Systems of Physics – Class 12
Answer» RIGHT answer is (d) The value of the harmonic is inversely proportional to its contribution to the waveform The explanation is: When the bandwidth is large enough to ACCOMMODATE a few harmonics, the INFORMATION is not lost and the rectangular signal is more or LESS recovered. This is so because the HIGHER the harmonic, the less is its contribution to the waveform. Therefore, the value of the harmonic is inversely proportional to its contribution to the waveform.

56.	The communication system needed for a given signal depends on which of the following?(a) Band of frequencies(b) Length of the channel(c) Size of the transmitter(d) Size of the collectorThe question was asked in semester exam.The question is from Communication Systems topic in portion Communication Systems of Physics – Class 12
Answer» Right answer is (a) Band of frequencies To ELABORATE: Each of the message signals has different RANGES of frequencies. The type of communication system needed for a GIVEN signal depends on the bad of frequencies which are considered ESSENTIAL for the communication process.

57.	What happens in frequency modulation?(a) The amplitude of the modulated wave varies as the frequency of the carrier wave(b) The frequency of the modulated wave varies as the amplitude of the modulating wave(c) The amplitude of the modulated wave varies as the amplitude of the carrier wave(d) The frequency of modulated wave varies as the frequency of modulating waveThis question was addressed to me in a national level competition.My question is from Communication Systems in section Communication Systems of Physics – Class 12
Answer» The correct answer is (b) The FREQUENCY of the MODULATED wave VARIES as the AMPLITUDE of the modulating wave Easy explanation: The frequency of the modulated wave varies as the amplitude of the modulating wave. To generate a frequency modulated signal, the frequency of the radio CARRIER is changed in line with the amplitude of the incoming audio signal.

58.	The range of radio frequencies for communication through free space is which of the following?(a) Few hundreds of Hz to a few kHz(b) Few hundreds of MHz to a few GHz(c) Few hundreds of kHz to a few GHz(d) Few hundreds of Hz to a few thousands kHzThe question was posed to me during an online interview.I'm obligated to ask this question of Communication Systems in division Communication Systems of Physics – Class 12
Answer» Right option is (C) Few HUNDREDS of kHz to a few GHz The explanation: Communication through free space using radio WAVES TAKES place over a very wide range of FREQUENCIES, i.e. from a few hundreds of Hz to a few kHz. This range of frequencies is further subdivided and allocated for various services.

59.	A carrier of peak voltage 15 V is used to transmit a message signal. If the modulation index is 70%, then what will be the peak voltage of the modulating signal?(a) 25 V(b) 11 V(c) 10.5 V(d) 30 VI had been asked this question in a national level competition.This intriguing question comes from Communication Systems topic in chapter Communication Systems of Physics – Class 12
Answer» The correct option is (c) 10.5 V To EXPLAIN: μ = \(\FRAC {A_m}{A_c}\). Am = μ × Ac. Am = \( ( \frac {70}{100})\) × 15 V Am = 10.5 V.

60.	‘X’ refers to the frequency range over which equipment operates or the range over which the frequencies in a signal vary. Identify ‘X’.(a) Range(b) Repeater(c) Bandwidth(d) BasebandThis question was posed to me in final exam.My doubt stems from Basic Terminology Used in Electronic Communication Systems in portion Communication Systems of Physics – Class 12
Answer» Correct OPTION is (c) BANDWIDTH To EXPLAIN I would say: Bandwidth refers to the frequency range over which EQUIPMENT operates or the range over which the frequencies in a signal vary. It is the particular range of frequencies for transmitting a signal. THEREFORE, X is bandwidth.

61.	Identify the device which is a combination of a transmitter, an amplifier and a receiver which picks up a signal and retransmits it.(a) Multi-tandem transmitter(b) Repeater(c) Amplifier(d) ModemThis question was addressed to me in a job interview.The doubt is from Basic Terminology Used in Electronic Communication Systems in portion Communication Systems of Physics – Class 12
Answer» RIGHT CHOICE is (b) Repeater Best EXPLANATION: A repeater is a combination of a transmitter, an AMPLIFIER and a receiver which picks up a signal from the transmitter, amplifies and retransmits it to the receiver sometimes with a change of carrier frequency.

62.	A channel can be either in the form of wires or wireless.(a) True(b) FalseI have been asked this question in exam.Asked question is from Elements of a Communication System topic in section Communication Systems of Physics – Class 12
Answer» Correct option is (a) TRUE The explanation is: YES, this is a true statement. Depending upon the type of the communication SYSTEM, a channel can be in the FORM of wires or cables CONNECTING the transmitter and the receiver or it can also be wireless.

63.	‘X’ for an AM is the ratio of change in amplitude of the carrier wave to the amplitude of the original carrier wave. Identify ‘X’.(a) Automatic gain control(b) Modulation index(c) Phase index(d) Amplitude indexThis question was posed to me in an online quiz.My question comes from Communication Systems in section Communication Systems of Physics – Class 12
Answer» Right choice is (b) Modulation INDEX The explanation: The modulation index for an AM WAVE is DEFINED as the ratio of change in the amplitude of the CARRIER wave to the amplitude of the original carrier wave. μ = \(\FRAC {(Change \, in \, the \, amplitude \, of \, the \, carrier \, wave)}{(Amplitude \, of \, the \, original \, carrier \, wave)}\).

64.	The bandwidth of optic fiber is high.(a) True(b) FalseThis question was addressed to me by my school teacher while I was bunking the class.I'd like to ask this question from Communication Systems in section Communication Systems of Physics – Class 12
Answer» Right option is (a) True Explanation: Yes, this is a true statement. The bandwidth of optic fiber is high due to the speed with which data can be TRANSMITTED and also the RANGE of frequencies over which the data can travel without any attenuation. An optical fiber can offer a transmission bandwidth in excess of 100 GHz.

65.	Pick out the expansion of ITU.(a) Internal Telecommunication Union(b) International Telephone Union(c) International Telecommunication University(d) International Telecommunication UnionThis question was addressed to me during an interview for a job.My doubt stems from Communication Systems in portion Communication Systems of Physics – Class 12
Answer» Right OPTION is (d) International TELECOMMUNICATION UNION To ELABORATE: The expansion of ITU is the International Telecommunication Union. It is a specialized agency of the United Nations that is RESPONSIBLE for all the matters related to information and communication technologies. The ITU administers the present system of frequency allocations