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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
In AM waves, the amplitude of each side band frequency isA. `E_(c)`B. `mE_(c)`C. `(mE_(c))/2`D. 2mE |
| Answer» Correct Answer - C | |
| 52. |
Calculate modulation index of an FM signal in which modulating frequency is 2 k Hz and maximum deviation is 10 k Hz. |
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Answer» Here, `v_m = 2k Hz, lambda_(max) = 10k Hz` As `m_f = lambda_(max)/v_(m) :. m_(f) = 10/2 = 5` . |
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| 53. |
In amplitude modulation, sinusoidal carrier frequency used is denoted by `omega_(c)` and the signal frequency is denoted by `omega_(m)`. The handwidth `(Deltaomega_(m))` of the signal is such that `Deltaomega_(m)ltltomega_(c)`. Which of the following frequency is no =t contained in the modulated wave.A. `omega_(m)+omega_(c)`B. `omega_(c)-omega_(m)`C. `omega_(m)`D. All of these |
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Answer» Modulated wave has three frequencies `(omega_(m)+omega_(c)),omega_(c)` and `(omega_(c)-omega_(m))` It means `omega_(m)` is exluded. Thus option (c) is true. |
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| 54. |
A male voice after modulation-transmission sounds like that of a female to the receiver. The problem is due toA. Poor selection of modulation index (selected `0 lt m lt 1`)B. Poor bandwidth selection of amplifiersC. Poor selection of carrier frequencyD. Loss of energy in transmission |
| Answer» Correct Answer - B | |
| 55. |
What is modulation index of an FM wave ? |
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Answer» Modulation Index of FM wave `= ("maximum frequency deviation") /("modulation frequency")` `m_f = delta_(max)/v_m`. |
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| 56. |
A male voice after modulation-transmission sounds like that of a female to the receiver. The problem is due toA. poor selection of modulation index (selected 0 lt m lt 1)B. poor bandwidth selection of amplifiersC. poor selection of carrier frequencyD. loss of energy in transmission |
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Answer» Correct Answer - B The frequency of the female voice (pitch) is more than that of a male voice. In this case male voice after modulation sounds like a female voice in the receiver. This indicates that the frequency at the receiver end is more than that at the transmitter end. This happens due to poor bandwidth selection of the amplifier . In A.M., the bandwidth is twice the frequency of the modulating signal |
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| 57. |
What is the modulation index of an over modulated waveA. 1B. zeroC. `lt1`D. `gt1` |
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Answer» Correct Answer - D When `m_(a)gt1` then carrier is said to be over modulated. |
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| 58. |
In an amplitude modulation with modulation index 0.5 the ratio of the carrier wave to that of side band in the modulated wave isA. 4:1B. 1:2C. 1:1D. 2:1 |
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Answer» Here, `mu=0.5`, Amplitude of carrier wave `=A_(c)` Ratio `=(A_(c))/(muA_(c))xx2=(2)/(mu)=(2)/(0.5)=(4)/(1)=4:1` |
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| 59. |
The original electrical information signal to be transmitted is called asA. modulating signalB. base band signalC. carrier signalD. information /source signal |
| Answer» Correct Answer - D | |
| 60. |
What is modulation? In the given block diagram of a receiver for detection of amplitude modulated wave write the name of part X. |
| Answer» Intermediate frequency `(IF)` stage in adiition to facilitate further processing the carrier frequency is usually changed to a lower frequency y what is called an intermediate frequency `(IF)` stage precending the detection. | |
| 61. |
The waves used in telecommunication areA. IRB. UVC. MicrowaveD. Cosmic rays |
| Answer» Correct Answer - C | |
| 62. |
Find the amplitude of side bands in the above problem in terms of modulation index `mu` and carrier wave amplitude `A_c`. |
| Answer» Correct Answer - `(muA_c)/2` | |
| 63. |
What is the changed in amplitude modulation? |
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Answer» Amplitude of high frequency carrier wave is made proportional to the instantaneous amplitude of audio frequency nodulating voltage. |
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| 64. |
What is the meant by deviation in frequency of FM wave? |
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Answer» Deviation in frequency, `delta = v-v_c`, where `v_c` is constant frequency of carrier wave and v is instantaneous frequency of the FM wave at any time t. |
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| 65. |
How many number of satellites are needed for global communications? |
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Answer» Three satellites which are situated at an angular separation of `120^@` from each other, while orbiting around earth. |
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| 66. |
STATEMENT-1: In amplitude modulation, the frequency of amplitude variation is much smaller than the frequency of modulated wave STATEMENT-2 : Frequency of the signal is much smaller than the frequency of the carrier waveA. Statement-1 is True. Statement-2 is True Statement-2 is a correct explanation for statement-3B. Statement is True Statement-2 is True Statement-2 is NOT a correct explanation for Statement-3C. Statement-1 Is True Statement-2 is FalseD. Statement-1 is False. Statement 2 is True |
| Answer» Correct Answer - A | |
| 67. |
Major parts of communications systems are:A. transmitter and receiverB. receiver and communication channelC. transmitter and communication channelD. transmitter , receiver and communication channel |
| Answer» Correct Answer - D | |
| 68. |
An amplitude modulated wave is as shown in the figure. What is the percentage of modulation ? A. 0.5B. 0.6667C. 0.45D. 0.556 |
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Answer» Correct Answer - B From the figure, we find that Maximum voltage =`100/2`=50 V Minimum voltage =`20/2`=10 V Percentage modulation `mu=(V_"max"-V_"min")/(V_"max"+V_"min")xx100=((50-10)/(50+10))xx100` `=40/60xx100=66.67%` |
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| 69. |
What type of modulation is employed in india for radio transmissionA. amplitude modulationB. frequency modulationC. pulse modulationD. none of these |
| Answer» Correct Answer - A | |
| 70. |
Which of the following systems are digital ?A. clinical thermometerB. electronic counter used to count the persons visiting an exhibitionC. electronic calculatorD. both b and c |
| Answer» Correct Answer - D | |
| 71. |
A digital signal-A. is less reliable than analog signalB. is more reliable than analog signalC. is equally reliable as the analog signalD. not reliable |
| Answer» Correct Answer - B | |
| 72. |
What is the range of values of modulation index of an AM wave? |
| Answer» Modulation index of an AM wave lies between 0 and 1. | |
| 73. |
What is varied in a FM wave? |
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Answer» In frequency modulation, the frequency of carrier wave is varied in accordance with the instantaneous value of the modulating voltage. |
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| 74. |
In amplitude modulation, the modulation index mu, is kept less than or equal to 1 because.A. ` m gt 1` , will result in interference between carrier frequency and message frequency , resulting into distortionB. ` m gt 1` will result in overlapping of both side bands resulting into loss of informationC. `m gt 1` will result in change in phase between carrier signal and message signalD. ` m gt 1` indicates amplitude of message signal greater than amplitude of carrier signal resulting into distortion |
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Answer» Correct Answer - B::D The modulation index (m) of amplitude modulated wave is `m = (" amplitude of message signal" (A_(m)))/("amplitude of carrier signal" (A_(c)))` If `m gt 1 , then A_(m) gt A_(c)`. In this situation , there will be distortion of the resulting signal of amplitude modulated wave . Maximum modulation frequency `(m_(f)) of AM` wave is `m_(f) =(Deltav_(max))/(v_(m(max))) =("frequency deviation")/("maximum frequency value of modulating wave")` If `m_(f) gt 1` , then `Delta v_(max) gt v_(m)` . It means , there will be overlapping of both side bands of modulated wave resulting into loss of information. |
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| 75. |
Major parts of communications systems are:A. transmitter and receiverB. receiver and communication channelC. transmitter and communication channelD. transmitter, receiver and communication channel |
| Answer» Correct Answer - D | |
| 76. |
In the process of modulation, the radio frequency wave is known asA. a modulating waveB. a modulated waveC. a carrier waveD. a demodulated wave |
| Answer» Correct Answer - C | |
| 77. |
In frequency modulation, the frequency of the modulated wave varies asA. frequency of the modulating waveB. amplitude of the modulating waveC. frequency of the carrier waveD. intensity of the modulating wave |
| Answer» Correct Answer - B | |
| 78. |
A digital signal possessA. continuously verying valuesB. only two discrete valuesC. only four discrete valuesD. only five discrete values |
| Answer» Correct Answer - B | |
| 79. |
What is total modulation index when a carrier wave is modulated by a number of sine waves having modulation index `mu_1, mu_2, mu_3, …….mu_n`? |
| Answer» `mu_A = sqrt(mu_(1)^(2) + mu_(2)^(2) + mu_(3)^(2) + ………)`. | |
| 80. |
If a number of sine waves with modulation indices `n_(1),n_(2),n_(3)`… modulate a carrier wave, then total modulation index (n) of the wave isA. `n_(1)+n_(2)…. +2(n_(1)+n_(2)…..)`B. `sqrt(n_(1)-n_(2)+n_(3)…..)`C. `sqrt(n_(1)^(2)+n_(2)^(2)+n_(3)^(2)….)`D. none of these |
| Answer» Correct Answer - C | |
| 81. |
Modulation is the process of superposingA. low frequency audio signal of high frequency wavesB. low frequency radio signal on low frequency audio wavesC. high frequency ratio signal on low frequency audio signalD. low fequency radio signal on high frequency audio waves. |
| Answer» Modulatation is the process of superposing the low frequency audio signal on high frequency wave. | |
| 82. |
Communication channel consist of:A. transmission lineB. optical fibreC. free spaceD. all of the above |
| Answer» Correct Answer - D | |
| 83. |
Basic components of a transmitter are:A. message signal generator and antennaB. modulator and antennaC. signal generator and modulator and antennaD. message signal generator, modulator and antenna |
| Answer» Correct Answer - D | |
| 84. |
The frequency of a FM transmitter without signal input is calledA. Lower side band frequencyB. Upper side band frequencyC. Resting frequencyD. Critical frequency |
| Answer» Correct Answer - C | |
| 85. |
A carrier wave is modulated by n number of sine waves with modulation indices `mu_(1),mu_(2),mu_(3)+`.... The total modulation index `(mu)` of the wave isA. `mu_(1)+mu_(2)+mu_(3)+`....B. `sqrt(u_(1)^(2)+mu_(2)^(2)+mu_(3)^(2)+....)`C. `[(mu_(1)^(2)+mu_(2)^(2)+mu_(3)^(3)+....)/(n)]^(1//2)`D. `[(n)/(mu_(1)^(2)+mu_(2)^(3)+mu_(3)^(2)+......)]^(1//2)` |
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Answer» The total amplitude modulation index when a carrier wave is modulated by several sine waves simultaneously is given by `musqrt(mu_(1)^(2)+mu_(2)^(2)+mu_(3)^(2)+....)`. |
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| 86. |
For what value of `m_(a)` will the total power per cycle be maximum in the modulated wave?A. zeroB. TC. `1//2`D. `gt1` |
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Answer» As `p_(t)=p_(c)(1_(m_(a)^(2))/(2))` where `m_(a)` is the amplitude modulation index. Power `(P_(t))` will be maximum if the value of `m_(a)` is maximum i.e. `m_(a)=1` `therefore P_("max")=P_(c)(1+(1^(2))/(2))=(3)/(2)P_(c)=15P_(c)` Hence option (d) s true. |
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| 87. |
Basic components of a transmitter are:A. message signal generator and antennaB. modulator and antennaC. signal generator and modulatorD. message signal generator, modulator and antenna |
| Answer» Correct Answer - D | |
| 88. |
A device that converts one from of energy into another form is termed asA. a transducerB. a transmitterC. an amplifierD. a receiver |
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Answer» Correct Answer - A Transducer : e.g. microphone , loudspeaker , photocell, etc. |
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| 89. |
The message signalA. analog onlyB. digital onlyC. analog and digitalD. analog or digital |
| Answer» Correct Answer - D | |
| 90. |
A loud speaker convertsA. electrical signals into sound signalsB. sound signals into electrical signalsC. both (1) and (2) aboveD. neither (1) nor (2) |
| Answer» Correct Answer - A | |
| 91. |
A microphone convertsA. sound signals into electrical signalsB. electrical signals into sound signalsC. both (1) and (2) aboveD. neither (1) nor (2) |
| Answer» Correct Answer - A | |
| 92. |
Three waves A,B and C of frequencies 1600 kHz, 5 MHz and 60 MHz, respectively are to be transmitted from one place to another.Which of the following is the appropriate mode of communication?A. A is transmitted via space wave while B and C are transmitted via sky spaceB. A is transmitted via ground wave, B via sky wave and C via space waveC. B and C are transmitted via ground wave while A is transmitted via sky waveD. B is transmitted via ground wave while A and C are transmitted vai space wave |
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Answer» Correct Answer - B Mode of communication depends upon the frequency range. (b) is the correct choice. The frequency (A) of 1600 Hz is transmitted via ground wave, B(v= Hz) is transmitted via sky wave and C (v=60 MHz) is transmitted via space wave. |
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| 93. |
A ` 1 KW ` signal is transmitted using a communication channel which provides attenuatiom at the rate of ` - 2 dB per km` . If the communication channel has a total length of ` 5 km` , the power of the signal received is [ gain in `dB = 10 log ((P_(0))/(P_(i)))]`A. `900 W`B. `100 W`C. `990 W`D. `1010 W` |
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Answer» Correct Answer - B Here `P_(i) = 1 kW = 1000` watt , length of path `= 5 km , P_(0) = ?` Loss of power at a distance of ` 5 km = - 2 xx 5 = - 10 dB`. As gain in `dB = 10 log .(P_(0))/(P_(i)) :. - 10 = log .(P_(0))/(P_(i)) = - 10 log .(P_(i))/(P_(0))` or `log .(P_(i))/(P_(0)) = 1 = log 10 or (P_(i))/(P_(0)) = 10 or P_(0) = (P_(i))/(10) = (1000)/(10) = 100` watt |
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| 94. |
Assertion: The surface wave propagation is used for medium frequency and low frequency band. Reason: The attenuation of surface waves increased with increase in frequency.A. both, Assertion and Reason are true and the Reason is the correct explanation of the Assertion.B. both, Assertion and Reason are true but Reason is not a correct explanation of the Assertion.C. Assertion is true but the Reason is false.D. both, Assertion and Reason are false. |
| Answer» Both the assertion and reason are correct and reason is correct explanation of the assertion. | |
| 95. |
is the set up used in the transimiision of information from one place to another. The present day communication systems are electrical, electronic or optical in nature. Three parts of a communication system are: Transmitter: Communication Channer and Receiver. A signal is defined as a single valued function of time. This function has a unique value at every instant of time. Most of the speech or information signals cannot be transmitted directly over long distances. They have to be modulated suitably and then trasmitted. Communication channer carries the modulated wave from transmitter to receiver. The air, transmission lines and free space are the common communication channels. the reciever consisits of a pickup antenna, a with the help of the above passage, choose the most appropriate alternative to each of the following questions: Communication systems may beA. electricalB. electronicC. opticalD. any of the above |
| Answer» Communication systems may be electrical, electronic or optical in nature. | |
| 96. |
Assertion: Satellite is an ideal platform for remote sensing. Reasion: Satellite in poplar orbit can provide global coverage or continuous coverage of the fixed area in geostationary configuration.A. Statement-1 is true: Statement-2 is true, and Statement-2 is correct explanation of Statement-1.B. Statement-1 is true, Statement-2 is true, but Sttement-2 is not a correct explanation of Statement-1.C. Statement-1 is true, but Statement-2 is false.D. Statement-1 is false, but Statement-2 is true. |
| Answer» Both the statement are correct and statement-2 is correct explanation of statement-1. | |
| 97. |
Statement-1: Radio waves can be polarised. Statement-2: Sound waves in air are longitudinal in nature.A. Statement-1 is true: Statement-2 is true, and Statement-2 is correct explanation of Statement-1.B. Statement-1 is true, Statement-2 is true, but Sttement-2 is not a correct explanation of Statement-1.C. Statement-1 is true, but Statement-2 is false.D. Statement-1 is false, but Statement-2 is true. |
| Answer» both the statements are correct but the statements-2 is not correct explanation of statement-1. | |
| 98. |
If a carrier wave of 1000 kHz is used to carry the signal, the length of transmitting antenna will be equal to -A. 3 mB. 30 mC. 75 mD. 3000 m |
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Answer» Correct Answer - C `l = lambda/4` Now ` v = nlambda` ` :. lambda = v/n` Thus ` l = v/(4n)` ` = (3 xx 10^(8))/(4 xx 10^(3) xx 10^(3))` ` = 0.75 xx 10^(2)` ` = 75` m |
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| 99. |
When the antenna is held parallel to horizontal surface of earth , the electromagnetic wave would be ………. Polarised. |
| Answer» Correct Answer - horizontally | |
| 100. |
Name the two basic modes of communication. Which one is used for telephonic communication? |
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Answer» Two basic modes of communication are : (i) point to point mode (ii) broadcast mode. For telephonic communication, point to point mode is used. |
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