NEET Physics Class 12 Chapter 5 Principles Of Communication MCQ’s

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Chapter 5 Principles Of Communication Multiple Choice Questions Exercise-1

Question 1. A digital signal –

  1. Is less reliable than analog signal
  2. Is more reliable than analog signal
  3. Is equally reliable as the analog signal
  4. Signal reliability meaning

Answer: 2. Is more reliable than analog signal

Question 2. Modern communication systems use

  1. Analog circuits
  2. Digital circuits
  3. Combination of analog and digital circuits
  4. Discrete circuits

Answer: 2. Digital circuits

Question 3. The audio signal –

  1. Can be sent directly over the air for large distance
  2. Cannot be sent directly over the air for large distance
  3. Possess very high frequency
  4. Posses very high intently

Answer: 2. Cannot be sent directly over the air for large distance

Question 4. The process of changing some characteristic of a carrier wave per the intensity of the signal is called –

  1. Amplification
  2. Rectification
  3. Modulation
  4. Normalization

Answer: 3. Modulation

Question 5. If a carrier wave of 1000 kHz is used to carry the signal, minimum the length of the transmitting antenna will be equal to –

  1. 300 M
  2. 150 M
  3. 75 M
  4. 750 M

Answer: 3. 75 M

Question 6. The type of modulation used for continuous wave and analog signal are –

  1. One only
  2. Two only
  3. Three only
  4. None of these

Answer: 3. Three only

Question 7. In amplitude modulation what changes in the carrier wave –

  1. Only the amplitude is changed but the frequency remains the same
  2. Both the amplitude and frequency change equally
  3. The amplitude and frequency change unequally
  4. Only phase changes

Answer: 1. Only the amplitude is changed but the frequency remains the same

Question 8. Modulation factor determines –

  1. Only the strength of the transmitted signal
  2. Only the quality of the transmitted signal
  3. Both the strength and quality of the signal
  4. None of the above

Answer: 3. Only the quality of the transmitted signal

Question 9. The degree of modulation is kept –

  1. At any value
  2. Less than 100%
  3. Greater than 100 %
  4. May be at any value from 100% to 200%

Answer: 2. Less than 100%

Question 10. If the maximum and minimum voltage of an am wave are vmax. And vmin. Respectively the modulation factor–

  1. \(m=\frac{v_{\text {max. }}}{V_{\text {max. }}+V_{\text {min. }}}\)
  2. \(m=\frac{v_{\text {min. }}}{V_{\text {max. }}+V_{\text {min. }}}\)
  3. \(m=\frac{v_{\text {max. }}+V_{\text {min. }}}{V_{\text {max. }}-V_{\text {min } .}}\)
  4. \(m=\frac{v_{\text {max. }}-V_{\text {min. }}}{V_{\text {max. }}+V_{\text {min. }}}\)

Answer: 4. \(m=\frac{v_{\text {max. }}-V_{\text {min. }}}{V_{\text {max. }}+V_{\text {min. }}}\)

Question 11. The am wave contains three frequencies, viz :

  1. \(\frac{f_c}{2}, \frac{f_c+f_s}{2}, \frac{f_c-f_s}{2}\)
  2. 2Fc, 2(fc + fs), 2(fc –fs)
  3. Fc,(fc + fs), (fc – fs)
  4. Fc, fc, fc

Answer: 3. Fc,FC + fs), (fc – fs)

Question 12. In a wave, carrier power is given by

  1. \(p_c=\frac{2 e_c^2}{r}\)
  2. \(p_c=\frac{e_c^2}{r}\)
  3. \(p_c=\frac{e_c^2}{2 r}\)
  4. \(p_c=\frac{e_c^2}{\sqrt{2} r}\)

Answer: 3. \(p_c=\frac{e_c^2}{2 r}\)

Question 13. The fraction of total power carried by side bands is given by\

  1. \(\frac{p_s}{p_t}=m^2\)
  2. \(\frac{p_s}{p_t}=\frac{1}{m^2}\)
  3. \(\frac{p_s}{p_t}=\frac{2+m^2}{m^2}\)
  4. \(\frac{p_s}{p_t}=\frac{m^2}{2+m^2}\)

Answer: 4. \(\frac{p_s}{p_t}=\frac{m^2}{2+m^2}\)

Question 14. Which of the following is/are the limitations of amplitude modulation?

  1. Clear reception
  2. High efficiency
  3. Small operating range
  4. Good audio quality

Answer: 3. Small operating range

Question 15. To avoid noise the frequency above which transmission of electrical energy is practical?

  1. 0.2 khz
  2. 2Khz
  3. 20 Khz
  4. 200Khz

Answer: 3. 20 Khz

Question 16. What type of modulation is employed in India for radio transmission?

  1. Pulse modulation
  2. Frequency modulation
  3. Amplitude modulation
  4. None of these

Answer: 3. Amplitude modulation

Question 17. For a carrier frequency of 100 kHz and a modulating frequency of 5 khz what is the bandwidth of a transmission–

  1. 5 kHz
  2. 10Khz
  3. 20 kHz
  4. 200 kHz

Answer: 2. 10Khz

Question 18. Which one of the following subsystems is used for the satellite’s orbit position and altitude?

  1. Thrust subsystem
  2. Power subsystem
  3. Antenna subsystem
  4. Stabilization subsystem

Answer: 1. Thrust subsystem

Question 19. Intelsat satellite works as a:

  1. Transmitter
  2. Repeater
  3. Absorber
  4. None of these

Answer: 2. Repeater

Question 20. Intelsat satellite is used for:

  1. In-house radio communication
  2. Intercontinental communication
  3. Radar communication
  4. None of the above

Answer: 2. Intercontinental communication

Question 21. A geosynchronous satellite is :

  1. Located at a height of 35,860 km to ensure global coverage
  2. Appears stationary over the Earth’s magnetic pole
  3. Not stationary at all, but orbits the earth 24 hrs
  4. Motionless in space (except for its spin)

Answer: 3. Not stationary at all, but orbits the earth 24 hrs

Question 22. The frequency band used for radar relay systems and television –

  1. Uhf
  2. Vlf
  3. Vhf
  4. Ehf

Answer: 1. Uhf

Question 23. Fading applies to :

  1. Troposcatter propagation
  2. Ionospheric propagation
  3. Faraday rotation
  4. Atmospheric storms

Answer: 1. Troposcatter propagation

Question 24. When microwave signals follow the curvature of the earth, this is known as :

  1. Window
  2. The faraday effect
  3. Ionospheric reflection
  4. Ducting

Answer: 4. Ducting

Question 25. In which of the regions of the earth’s atmosphere temperature decreases with height?

  1. Ionosphere
  2. Stratosphere
  3. Troposphere
  4. Mesosphere

Answer: 3. Troposphere

Question 26. Major parts of a communications system are :

  1. Transmitter and modulator receiver
  2. Receiver demodulator and communication channel
  3. Transmitter and communication channel
  4. Transmitter, receiver, and communication channel

Answer: 4. Transmitter, receiver, and communication channel

Question 27. Communication channels may consist of :

  1. Transmission line
  2. Optical fiber
  3. Free space
  4. All of the above

Answer: 4. All of the above

Question 28. The basic components of a transmitter are :

  1. Message signal generator and antenna
  2. Modulator and antenna
  3. Signal generator and modulator
  4. Message signal generator, modulator, and antenna

Answer: 4. Message signal generator, modulator, and antenna

Question 29. The message signal can be :

  1. Analog only
  2. Digital only
  3. Analog and digital
  4. Analog or digital

Answer: 4. Analog or digital

Question 30. A microphone converts

  1. Sound signals into electrical signals
  2. Electrical signals into sound signals
  3. Both and above
  4. Neither nor (2)

Answer: 1. Sound signals into electrical signals

Question 31. A loudspeaker converts

  1. Electrical signals into sound signals
  2. Sound signals into electrical signals
  3. Both and above
  4. Neither nor (2)

Answer: 1. Electrical signals into sound signals

Question 32. Which is more advantageous?

  1. Analog data communication
  2. Digital data communication?
  3. Analog data communication
  4. Digital data communication
  5. Both are equally good
  6. Depends on the application

Answer: 2. Digital data communication

Question 33. The message signal is usually of :

  1. Audio frequency range
  2. Radiofrequency range
  3. Audio or radio frequency range
  4. Mixture of both

Answer: 1. Audio frequency range

Question 34. Modulation is the phenomenon of :

  1. Superimposing the audio frequency signal over a carrier wave
  2. Separating the audio frequency signal from the carrier wave
  3. Separating carrier wave from the modulated wave
  4. Any of (1),(2),above

Answer: 1. Superimposing the audio frequency signal over a carrier wave

Question 35. In amplitude modulation, carrier wave frequencies are:

  1. Lower compared to those in frequency modulation
  2. Higher compared to those in frequency modulation
  3. Same as in frequency modulation
  4. Lower sometimes and higher sometimes than those in frequency modulation

Answer: 1. Lower compared to those in frequency modulation

Question 36. The transmission media can be :

  1. Guided only
  2. Unguided only
  3. Both and
  4. Neither nor (2)

Answer: 3. Both and

Question 37. A 1000 kHz carrier is modulated with 800 hz audio signals. What are the frequencies of the first pair of sidebands:

  1. 1000.8 khz, 999.2 khz
  2. 999.2 kHz, 998.4 kHz
  3. 1001.6 khz, 1000.8 khz
  4. 1000 kHz, 800 Hz

Answer: 1. 1000.8 kHz, 999.2 kHz

Question 38. In an amplitude-modulated wave, for an audio frequency of 500 cps, the appropriate carrier frequency will be:

  1. 50 C/s
  2. 100 C/s
  3. 500 C/s
  4. 50000 C/s

Answer: 4. 50000 C/s

Question 39. In a.m., The total modulation index should not exceed one or else :

  1. The system will fail
  2. Distortion will result
  3. The amplifier will be damaged
  4. None of the above

Answer: 2. Distortion will result

Question 40. Electromagnetic waves are caused polarized because it –

  1. Undergoes reflection
  2. Undergoes refraction
  3. Transverse nature
  4. Longitudinal in nature

Answer: 3. Transverse nature

Question 41. The velocity of electromagnetic waves in a dielectric medium ( r = 4) is –

  1. 3 × 108 Metre/second
  2. 1.5 × 108 meter/second
  3. 6 × 108 Metre/second
  4. 7.5 ×107 metre/second

Answer: 4. 7.5 ×107 metre/second

Question 42. An ‘antenna’ is :

  1. Inductive
  2. Capacitive
  3. Resistive above its resonance frequency
  4. None of the above

Answer: 1. Inductive

Question 43. The characteristic impedance of a loss-less transmission line is given by

  1. \(z_0=\sqrt{l c}\)
  2. \(z_0=\sqrt{l / c}\)
  3. \(z_0=\sqrt{c / l}\)
  4. Z0 = lc

Answer: 2. \(z_0=\sqrt{l / c}\)

Question 44. The q of a resonant transmission line is

  1. \(q=\frac{\omega}{l r}\)
  2. \(q=\frac{\omega r}{l}\)
  3. \(q=\frac{l}{r}\)
  4. \(q=\frac{\omega l}{r}\)

Answer: 3. \(q=\frac{l}{r}\)

Question 45. The distance between consecutive maxima and minima on a transmission line is given by –

  1. λ/2
  2. 2λ
  3. λ
  4. λ/4

Answer: 4. λ/4

Question 46. Through which mode of propagation, the radiowaves can be sent from one place to another –

  1. Ground wave propagation
  2. Sky wave propagation
  3. Space wave propagation
  4. All of them

Answer: 4. All of them

Question 47. The frequencies of electromagnetic waves employed in space communication vary over a range of –

  1. 104 Hz to 107 Hz
  2. 104 Hz to 1011 Hz
  3. 1 Hz to 104 Hz
  4. 1 Hz to 1011 Hz

Answer: 2. 104 Hz to 1011 Hz

Question 48. The wavelength of electromagnetic waves employed for space communication lies in the range of-

  1. 1 Mm to 30 m
  2. 1Mm to 300 m
  3. 1 Mm to 3 km
  4. 1 Mm to 30 km

Answer: 4. 1 Mm to 30 km

Question 49. The radiowaves of frequency 300 MHz to 3000 MHz belong to –

  1. High-frequency band
  2. Very high frequency band
  3. Ultra high-frequency band
  4. Super high frequency band

Answer: 3. Ultra high frequency band

Question 50. The maximum range of ground or surface wave propagation depends on –

  1. The frequency of the radiowaves only
  2. The power of the transmitter only
  3. Both of them
  4. None of them

Answer: 3. Both of them

Question 51. In which frequencies range space waves are normally propagated –

  1. Hf
  2. Vhf
  3. Uhf
  4. Shf

Answer: 3. Uhf

Question 52. For television broadcasting, the frequency employed is normally –

  1. 30 – 300 M hz
  2. 30 – 300 G hz
  3. 30 – 300 K Hz
  4. 30 – 300 Hz

Answer: 1. 30 – 300 M hz

Question 53. The sound waves after being converted into electrical waves are not transmitted as such because –

  1. They travel with the speed of sound
  2. The frequency is not constant
  3. They are heavily absorbed by the atmosphere
  4. The height of the antenna has to be increased several times

Answer: 3. They are heavily absorbed by the atmosphere

Question 54. The process of superimposing signal frequency (i.e. Audio wave) on the carrier wave is known as –

  1. Transmission
  2. Reception
  3. Modulation
  4. Detection

Answer: 3. Modulation

Question 55. In an amplitude-modulated wave for an audio frequency of 500 cycles/second, the appropriate carrier frequency will be –

  1. 50 Cycles/sec
  2. 100 Cycles/sec
  3. 500 Cycles/sec
  4. 50,000 Cycles/sec

Answer: 4. 50,000 Cycles/sec

Question 56. The tv. The transmission tower in Delhi has a height of 240 m. The distance up to which the broadcast can be received, (taking the radius of earth to be 6.4 x 106 m) is –

  1. 100 Km
  2. 60 Km
  3. 55. Km
  4. 50 Km

Answer: 3. 55. Km

Question 57. Radio waves of constant amplitude can be generated with –

  1. Filter
  2. Rectifier
  3. Amplifier
  4. Oscillator

Answer: 4. Oscillator

Question 58. The range of frequencies allotted for commercial FM radio broadcasts is –

  1. 88 To 108 MHz
  2. 88 To 108 kHz
  3. 8 To 88 MHz
  4. 88 To 108 GHz

Answer: 1. 88 To 108 MHz

Question 59. Intel set satellite works as a –

  1. Transmitter
  2. Receiver
  3. Absorber
  4. Repeater

Answer: 4. Repeater

Question 60. The space waves that are affected seriously by atmospheric conditions are

  1. MF
  2. Hf
  3. Vhf
  4. Uhf

Answer: 4. Uhf

Question 61. A sky wave with a frequency of 55 MHz is incident on the d-region of Earth’s atmosphere at 45°. The angle of refraction is (electron density for d-region is 400 electron/cc.) –

  1. 60°
  2. 45°
  3. 30°
  4. 15°

Answer: 2. 45°

Question 62. Which of the following is not a transducer?

  1. Loudspeaker
  2. Amplifier
  3. Microphone
  4. Human ear

Answer: 2. Amplifier

Question 63. Am is used for broadcasting because:

  1. It is more noise-immune than other modulation systems
  2. It requires less transmitting power compared with other systems
  3. Its use avoids receiver complexity
  4. No other modulation system can provide the necessary bandwidth faithful transmission.

Answer: 3. Its use avoids receiver complexity

Question 64. If μ1 and μ2 are the refractive indices of the materials of the core and cladding of an optical fiber, then the loss of light due to its leakage can be minimized by having

  1. μ1 > μ2
  2. μ1 < μ2
  3. μ1 = μ2
  4. None of these

Answer: 1. μ1 > μ2

Question 65. An antenna behaves as a resonant circuit only when its length is

  1. \(\frac{\lambda}{2}\)
  2. \(\frac{\lambda}{4}\)
  3. λ
  4. \(\frac{\lambda}{2} \text { or integral multiple of } \frac{\lambda}{2}\)

Answer: 4. \(\frac{\lambda}{2} \text { or integral multiple of } \frac{\lambda}{2}\)

Question 66. The electromagnetic waves of frequency 2 MHz to 30 MHz are

  1. In-ground wave propagation
  2. In sky wave propagation
  3. In microwave propagation
  4. In satellite communication

Answer: 2. In sky wave propagation

Question 67. A laser is a coherent source because it contains

  1. Many wavelengths
  2. The uncoordinated wave of a particular wavelength
  3. Coordinated waves of many wavelengths
  4. Coordinated waves of a particular wavelength

Answer: 4. Coordinated waves of a particular wavelength

Question 68. Laser beams are used to measure long distances because

  1. They are monochromatic
  2. They are highly polarised
  3. They are highly interested
  4. They have a high degree of spatial coherence

Answer: 4. They have a high degree of spatial coherence

Question 69. An oscillator produces fm waves of frequency 2 khz with a variation of 10 khz. What is the modulating index

  1. 0.20
  2. 5.0
  3. 0.67
  4. 1.5

Answer: 2. 5.0

Question 70. The phenomenon by which light travels in optical fibers is

  1. Reflection
  2. Refraction
  3. Total internal reflection
  4. Transmission

Answer: 3. Total internal reflection

Question 71. Television signals on earth cannot be received at distances greater than 100 km from the transmission station. The reason behind this is that

  1. The receiver antenna is unable to detect the signal at a distance greater than 100 km
  2. The tv program consists of both audio and video signals
  3. TV signals are less powerful than radio signals.
  4. The surface of the earth is curved like a sphere

Answer: 4. The surface of the earth is curved like a sphere

Question 72. Advantages of optical fiber

  1. High bandwidth and em interference
  2. Low bandwidth and em interference
  3. High bandwidth, low transmission capacity, and no em interference
  4. High bandwidth, high data transmission capacity, and no em interference

Answer: 4. High bandwidth, high data transmission capacity, and no em interference

Question 73. Long distance short wave radio broadcasting uses

  1. Ground wave
  2. Ionospheric wave
  3. Direct wave
  4. Skywave

Answer: 3. Direct wave

Question 74. The characteristic impedance of a coaxial cable is of the order of

  1. 50Ω
  2. 200Ω
  3. 270Ω
  4. None of these

Answer: 3. 270Ω

Question 75. A laser beam of pulse power 1012 watts is focussed on an object is 10–4 cm2. The energy flux in watt/cm2 at the point of focus is

  1. 1020
  2. 1016
  3. 108
  4. 104

Answer: 2. 1016

Question 76. The carrier frequency generated by a tank circuit containing 1 nf. The capacitor and 10 h inductor is

  1. 1592 Hz
  2. 1592 Mhz
  3. 1592 Khz
  4. 159.2 hz

Answer: 3. 1592 Khz

Question 77. Broadcasting antennas are generally

  1. Omnidirectional type
  2. Vertical type
  3. Horizontal type
  4. None of these

Answer: 2. Vertical type

Question 78. The attenuation in optical fiber is mainly due to

  1. Absorption
  2. Scattering
  3. Neither absorption nor scattering
  4. Both 1 and 2

Answer: 4. Both 1 and 20

Question 79. The process of superimposing signal frequency (i.e., Audio wave) on the carrier wave is known as

  1. Transmission
  2. Reception
  3. Modulation
  4. Detection

Answer: 3. Modulation

Question 80. In short-wave communication waves which of the following frequencies will be reflected by the ionospheric layer, having electron density 1011 per m3

  1. 2 Mhz
  2. 10 Mhz
  3. 12 Mhz
  4. 18 Mhz

Answer: 1. 2 Mhz

Question 81. The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to

  1. H1/2
  2. H
  3. H3/2
  4. H

Answer: 1. H1/2

Question 82. A laser beam is used for carrying out surgery because it

  1. Is highly monochromatic
  2. Is highly coherent
  3. Is highly directional
  4. Can be sharply focussed

Answer: 4. Can be sharply focussed

Question 83. Consider telecommunication through optical fibers. Which of the following statements is not true

  1. Optical fibers may have homogeneous cores with suitable cladding
  2. Optical fibers can be of graded refractive index
  3. Optical fibers are subject to electromagnetic interference from outside
  4. Optical fibers have extremely low transmission los

Answer: 3. Optical fibers are subject to electromagnetic interference from outside

Chapter 5 Principles Of Communication Multiple Choice Questions Exercise -2

Question 1. A TV tower has a height of 150 m. What is the population density around the TV tower if the total population covered is 50 lakh?

  1. 82.6 km–2
  2. 800.6 km–2
  3. 828.6 km–2
  4. 876.6 km–2

Answer: 3. 828.6 km–2

Question 2. Calculate the phase velocity of an electromagnetic wave having electron density and frequency for the D layer, N = 400 electron/ cc, = 300 kHz –

  1. 3 × 108 m/s
  2. 3.75 × 108 m/s
  3. 6.8 × 108 m/s
  4. 1.1 × 109 m/s

Answer: 2. 3.75 × 108 m/s

Question 3. A step-index fiber has a relative refractive index of 0.88% What is the critical angle at the core-cladding interface (sin 84º24′ = 0.9912)

  1. 60º
  2. 75º
  3. 45º
  4. None of these

Answer: 4. None of these

Question 4. The maximum useable frequency (MUF) in the F-region layer is x when the critical frequency is 60 MHz and the angle of incidence is 70º. Then x is

  1. 150 MHz
  2. 170 MHz
  3. 175 MHz
  4. 190 MHz

Answer: 3. 175 MHz

Question 5. The velocity factor of a transmission line x, if the dielectric constant of the medium is 2.6, the value of x is

  1. 0.26
  2. 0.62
  3. 2.6
  4. 6.2

Answer: 2. 0.62

Chapter 5 Principles Of Communication Multiple Choice Questions Exercise – 3 Jee (Main) / Aieee Problems (Previous Years)

Question 1. This question has Statement –1 and Statement –2. Of the four choices given after the statements, choose the one that best describes the two statements. Statement 1: Sky wave signals are used for long-distance radio communication. These signals are in general, less stable than ground wave signals. Statement 2: The state of the ionosphere varies from hour to hour, day to day, and season to season.

  1. Statement –1 is true, statement –2 is false.
  2. Statement –1 is true, Statement –2 is true, Statement –2 is the correct explanation of Statement –1
  3. Statement –1 is true, Statement –2 is true, Statement –2 is not the correct explanation of Statement–1
  4. Statement–1 is false, Statement –2 is true

Answer: 4. Statement–1 is false, Statement –2 is true

Question 2. Which of the following four alternatives is not correct? We need modulation:

  1. To Reduce The Time Lag Between Transmission And Reception Of The Information Signal
  2. To Reduce The Size Of Antenna
  3. To Reduce The Fractional Band Width, That Is The Ratio Of The Signal Band Width To The Centre Frequency
  4. To Increase The Selectivity.

Answer: 2. To Reduce The Size Of Antenna

Question 3. A radar has a power of 1kW and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500m. The maximum distance upto which it can detect objects located on the surface of the earth (Radius of earth = 6.4 × 106 m) is:

  1. 80 km
  2. 16 km
  3. 40 km
  4. 64 km

Answer: 1. 80 km

Question 4. A diode detector is used to detect an amplitude-modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100-kilo ohm. Find the maximum modulated frequency that could be detected by it.

  1. 10.62 MHz
  2. 10.62 kHz
  3. 5.31 MHz
  4. 5.31 kHz

Answer: 2. 10.62 kHz

Question 5. A signal of 5 kHZ frequency is amplitude modulated on a carrier wave of frequency 2 MHz. The frequencies of the resultant signal is/are:

  1. 2 MHz only
  2. 2005 kHz, and 1995 kHz
  3. 2005 kHz, 2000 kHz and 1995 kHz
  4. 2000 kHz and 1995 kHz

Answer: 3. 2005 kHz, 2000 kHz and 1995 kHz

Question 6. Choose the correct statement :

  1. In amplitude modulation, the frequency of high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal
  2. In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.
  3. In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the frequency of the audio signal
  4. In amplitude modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal

Answer: 4. In amplitude modulation the amplitude of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal

Question 7. In amplitude modulation, the sinusoidal carrier frequency used is denoted by c and the signal frequency is denoted by m. The bandwidth (m) of the signal is such that m<< c. Which of the following frequencies is not contained in the modulated wave?

  1. ωc – ωm
  2. ωm
  3. ωc
  4. ωm + ωc

Answer: 2. ωm

Question 8. A telephonic communication service is working at a carrier frequency of 10 GHz. Only 10% of it is utilized for transmission. How many telephonic channels can be transmitted simultaneously if each channel requires a bandwidth of 5 kHz?

  1. 2×105
  2. 2 × 106
  3. 2 × 103
  4. 2 × 104

Answer: 1. 2×105

Question 9. A TV transmission tower has a height of 140 m and the height of the receiving antenna is 40 m. What is the maximum distance upto which signals can be broadcasted from this tower in LOS (Line of sight) mode? (Given : radius of earth = 6.4 × 106 m)

  1. 80 km
  2. 40 km
  3. 48 km
  4. 65 km

Answer: 4. 65 km

Question 10. An amplitude-modulated signal is plotted below :

NEET Physics Class 12 Notes Chapter 5 Principles Of Communication MCQs An amplitude modulated signal is plotted

Answer: 3.

Question 11. Which one of the following best describes the above signal?

  1. (9 + sin(2.5π × 105t))sin(2π × 104t) V
  2. (1 + 9sin(2π × 104t))sin(2.5π × 105t)V
  3. (9 + sin(2π × 104t))sin(2.5π × 105t)V
  4. (9 + sin(4π × 104t))sin(5π × 105t)V

Answer: 1. (9 + sin(2.5π × 105t))sin(2π × 104t) V

Question 12. A 100 V carrier wave is made to vary between 160 V and 40 V by a modulating signal. What is the modulation index?

  1. 0.4
  2. 0.6
  3. 0.5
  4. 0.3

Answer: 2. 0.6

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