NEET UG Physics Communication System MCQs

SUMMARY

• Main elements of the communication system are :
(1) Transmitter (2) Transmission channel and (3) Receiver.

• Transducer : The device which transforms one form of energy into another form of energy is called a transducer.

• Transmission Channel : Transmission channel is a link or medium between transmitter and receiver. The signals of information are propagating through this medium and received at receiver.

• Noise : Noise is an unwanted signal. They get admixed with the information signal in the transmission channel and distort the information signal.

• Signal : For a transmission, the information is transformed into electric signal is called a signal. There are two types of signals. (1) Analog signal and (2) Digital signal.

Communication Systems 263

• Bandwidth : In communication system the difference of maximum frequency and minimum frequency efficiently transmitted by the system is called the bandwidth of the system. The bandwidth of audio signal is 20 kHz and bandwidth of video signal is 4.2 MHz.

• Modulation : The process of superposing low frequency audio signals on high frequency is called modulation. Low frequency is called the modulating signal and high frequency wave is called the carrier waves. The resultant wave is known as modulated wave. There are three types of the modulation. (1) Amplitude modulation (AM), (2) Frequency modulation (FM) and (3) Phase modulation (PM).

• Amplitude Modulation : A modulation in which the amplitude of the carrier wave is changed according to instantaneous value of the modulating wave is called amplitude modulation. Here, phase and frequency of carrier wave remain unchanged. Modulation

Index : The ratio of the amplitude of modulating wave and amplitude of carrier wave is called a modulation index. m_a  = E_m/E_c  Value of ma is always less than 1. 

• Demodulation : The process of separating information signal from carrier wave is called demodulation. This process is performed in the receiver. The circuit which performs the process of demodulation is called a detector circuit. 

• Propagation of an Electromagnetic Waves : (1) The wave propagating along the surface of the earth are called ground wave or surface wave. The frequencies up to 2 MHz is propagating through ground waves. 

(2) The waves returned to the earth after getting reflected by the ionosphere at a height of about 60-400 km is known as sky waves. 2 MHz to 30 MHz frequencies are propagating through the sky waves. (3) The waves from the transmitting antenna, reaching a receiver in a straight line after the reflection from the ground are called space waves.

(1) Type of communication Possible by Modem duplex is _______.
(A) Half duplex
(B) Simplex
(C) Double Duplex
(D) Full duplex

(2) To transmit 1Kh_Z frequency signal, wave length of the signal should be m.
(A) 3×10³ 
(B) 3×10⁵
 (C) 3×10⁷ 
(D) 3×10¹⁰

(3) What should be the minimum length of the antenna capable of emitting audio signal of wave length l ?
(A) λ/4
(B) λ/8
(C) λ
(D) λ/2

(4) is used as a medium an space communication
(A) Two wire line
(B) Space
(C) Amplifier
(D) Optical fibre

(5) The band width of Audio signal is
(A) 20 H_Z 
(B) 20 KH_Z
 (C) 20 MH_z 
(D) 20 GH_z

(6) ground waves are polarised at direction.
(A) vertically upward
(B) horizontal
(C) tangential direction to the surface of the earth
(D) in all four.

(7) Intensity of electric field of ground waves is in of the distance travelled by it.
(A) Square
(B)inverse of root
(C) proportion
(D) inverse

(8) In radio and television broadcast, the information signal is in the form of
(A) analog signal
(B) digital signal
(C) Both analogy and digit signals
(D) neither analog nor digital signal

(9) In light modulation, which characteristic of the carrier light wave is varied?
(A) Amplitude
(B) Frequency
(C) Phase
(D) intensity

(10) Though which mode of communication can radio waves be sent from one Plate to another?
(A) Ground wave Propagation
(B) sky wave Propagation
(C) Space wave Propagation
(D) All of the above

(11) Which range of Frequencies is Suitable for sky wave Propagation ?
(A) 1 KH_z to 500 KH_z
 (B) 1 MH_z to 2 MH_z
(C) 2 MHz to 20 MH_z
 (D) Above 30 MH_z

(12) Which of the Following is not a component of communication System ?
(A) Transmitter
(B) Transmission channel
(C) Noise
(D) Receiver

(13) Device which transform one form of energy in to another form of energy is called a
(A) Transducer
(B) Transformer
(C) Transponder
(D) Transistor

(14) is a link between the transmitter and receiver
(A) Microphone
(B) Transmission Channel
(C) transducer
(D) telephone

(15) in the receiver section are used to reduce the level of noise signal
(A) filter circuit
(B) Modulator
(C) de modulator
(D) Amplifier

(16) The minimum distance a up to which T.V transmission from a T.V. tower of height h can be received is Proportional to
(A)h^1/2
 (B) h
(C) h^3/2 
(D) h2

(17) The energy attenuation in optical fibre is mainly due to
(A) absorption
(B) scattering
(C) both a and b
(D) neither absorption nor scattering

(18) The electromagnetic waves of frequency 2 MHz to 30 MHz are
(A) in ground wave propagation
(B) in sky wave propagation
(C) in micro wave propagation
(D) in satellite communication

(19) Coaxial cable offers a band width approximately MHz
(A) 1 (B) 20
(C) 250
(D) 1000

(20) Modulation is used to_____
(A) reduce the band width used
(B) separate the transmission of different areas
(C) ensure that information may be transmitted to long distance
(D) allow the use of practical antennas

(21) An antenna can transmit radiation with more efficiency.
(A) low frequency
(B) high frequency
(C) long wave length
(D) None of these

(22) For an amplitude modulated wave, the maximum amplitude is found to be 9V while the minimum amplitude is found to be 3V. The modulation index is
(A) 100%
(B) 75%
(C) 50%
(D) 25%

(23) AM is used for broadcasting because
(A) it is more noise innumerable than other modulation system
(B) it requires less transmitting power compared with other system
(C) it's are avoids receiver complexity....
(D) No other modulation system can provide the necessary band width faithful transmission 

(24) Frequencies in the UHF range normally propagation by means of
(A) ground waves
(B) sky waves
(C) surface waves
(D) space waves

(25) The area to be covered for T.V telecast is doubled. Then the height to transmitting antenna will have to be
(A) doubled
(B) halved
(C) quadrupled
(D) kept unchanged

(26) Which of the following is related to telecommunication
(A) X-rays
(B) r-rays
(C) sound wave
(D) microwaves

(27) Suppose the amplitade of modulated wave equal to the signal amplitude. Then modulatation is
(A) 10%
(B) 25%
(C) 50%
(D) 100%

(28) Space waves are generally propagated in
(A) UHF
(B) VHF
(C) HF
(D) None of there

(29) If the frequency of 3 KHz has to be transmitted through amplitude modulation. Which of the following frequency should use as a carrier frequency ?
(A) 30 Hz
(B) 300 Hz
(C) 3000 Hz
(D) 3 MHz

(30) The range of frequencies allotted for commercial FM radio broadcast is
(A) 88 to 108 MHz
(B)88 to 108 KHz
(C) 8 to 88 MHz
(D) 88 to 108 GHz

(31) The process of superimposing signal frequency on the carrier wave is known as
(A) transmission
(B) reception
(C) modulation
(D) detection

(32) A T.V tower has a height 150m. What is the population density around the T.V tower if the total population covered is 50 lakh ? (Reduse of earth = 6.4× 10⁶ m)
(A) 82.6/km²
(B) 800.6/km²
(C) 828.6/km²
(D) 876.6/km²

(33) In which frequency range, space waves are normally propagated ?
(A) HF
(B) VHF
(C) UHF
(D) SHF

(34) If M₁ & M₂ are the refractive indices of the material of core and cladding of an optical fibre, than the loss of light due to its leakage can be minimized by having
(A) M₁ > M₂
(B) M₁ < M₂
(C) M₁ = M₂
(D) None of these

(35) Through which mode of propagation, the raido waves can be sent from one place to another ?
(A) ground wave propagation
(B) sky wave propagation
(C) space wave propagation
(D) all of them

(36) A radio can tune to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wave lenght band ?
(A) 400m - 250m
(B) 40m - 25m
(C) 4m - 2.5m
(D) None of these

Assertion Reason type Question

In the following questaion from (37 to 40) statement-1 (Assertion) is followed by statement-2 (Reason) Each question has the following four choice out of which only one choice is correct

(a) Statement-1 is true, statement-2 is true.
      Statement-2 is a correct explanation for statement-1.

(b) Statement-1 is true, statement-2 is true, statement-2 is not a correct enplanation for statement-1.

(c) Statement-1 is true, statement-2 is false

(d) Statement-1 is false, statement-2 is true.

 

(41) The refractive inden of the ionosphere
(A) increase as we go from the lower to upper layer of the ionosphere
(B) decrease as we go from the lower to upper layer of the ionosphere
(C) remain the same through out the ionosphere
(D) is equal to unity

(42) A T.V tower has a height of 80 m. The maximum distance up to which T.V transmission can be received is equal to . (radius of earth = 6.4×106m)
(A) 16 km
(B) 32 km
(C) 80 km
(D) 160 km

(43) A receiving station on the ground is receiving a signal of frequency 10 MHz, then the mode of transmission is
(A) ground wave propagation
(B) sky wave propagation
(C) both ground wave and sky wave propagation
(D) neither ground wave nor sky wave propagation

 

(64) If a radio receiver amphifier all the signal frequencies equally well, it is said to have high
(A) fidality
(B) distortion
(C) sensibility
(D) sensitivity

(65) In frequency modulation
(A) the amplitude of modulated wave varies as frequency of carrier wave.
(B) the frequency of modulated wave varies as amplitude of modulating wave.
(C) The amplitude of modulated wave varies as amplitude of carrier wave.
(D) The frequency of modulated wave varies as frequency of modulating wave.

(66) A silicon optical fibre with a care diameter large enough has a care refractive inder of 1.50 and cladding refractive inder 1.47. The critical angle at the care cladding interface is _____ .
(A) 87.5°
(B) 78.5°
(C) 38.5°
(D) 45°

(67) In satellite communication
(1) The frequency used lies between 5 MHz and 1 MHz
(2) The uplink and downlink frequencies are different.
(3) The orbit of geostationary staellite lies in the equatorial plane at an indication of 0o.
In the above statements.
(A) Only 2 and 3 are true
(B) all are true
(C) Only 2 is true
(D) Only 1 and 3 are true

(68) A signal wave of frequency 12 KHz is modulated with a carrier wave of freaquency 2.51 MHz.The upper and lower side band frequency are respectively.
(A) 2512 Hz and 2508 KHz
(B) 2522 KHz and 2488 KHz
(C) 2502 KHz and 2498 KHz
(D) 2512 KHz and 2498 KHz

 

72) An insulater ared in a transmission line has dierectrie unstant equal to 0.25 What is the velocity factor of the transmission line ?
(A) 4/3
(B) 2
(C) 3/4
(D) 4

(73) What is the working principal of optical fibre ?
(A) Refraction
(B) Total internal reflection
(C) Dispersion
(D) Scattering

(74) For efficient transmission of a 100 MH_Z  frequency wave, the minimum lenght of an antenna should be
(A) 3 m
(B) 3/4 m
(C) 10 m
(D) 100 m

(75) A photo director area light of wavelenght 1400nm Band gap of the Semiconductor used in the photo detector is (h = 6.63×10^-34 JS ;C = 3×10⁸ m / s)
(A) 0.7eV
(B) leV
(C) 2 eV
(D) 2.5 eV

(76) In modulation procrss radio signal is called
(A) modulating wave
(B) Carrier wave
(C) modulated wave
(D) transmitting wave

(77) Tank Circuit Contains lnf capcpcitor and 10 microhenry inductor What is the carrier frequency generated by it ?
(A)1629 MH_z 
(B) 1592 MHz
 (C) 1582 MHz 
(D) 156.2 MHz

(78) The effective power radiated by an antenna varies
(A) inverscly as the lenght of antenna
(B) inverscly as the square of the length of the antenna
(C) directly as the lenght of antenna
(D) directly as the square of the lenght of the antenna

 

(85) For 100% modulation, What is the value of minimum amplitude (E_min)of the modulated wave ?
(A) Zero
(B) 1
(C) 2
(D) 3

(86) When electromagnetic waves enter the ionised layer of ionosphere, the relative permitting of the ionised layer
(A) remain constant
(B) appears to decreure
(C) appears to increare
(D) chenger randomly

(87) IN which of the following media the wave propagation occurs with out attenation ?
(A) Conductor
(B) perfect dielecrei medium
(C) Semi conductor
(D) None of the above

(88) The step index fibre has a relative refractive index difference of 0.86% what is the critical angle at the core cladding interface ?
(A) 28.4°
(B) 82.4°
(C) 24.8°
(D) 75.6°

(89) A silicon optical fibre has a core refractive index of 1.50 and a cladding refractive inden 1.47 what is the numerical aperture of the fibre ?
(A) 0.90
(B) 0.60
(C) 0.45
(D) 0.30

(90) Which of the following alternative is not nature Noise ?
(A) Thunder of light
(B) Radiation coming from sun.
(C) Radiation coming from stars
(D) Radiation produced by flickering of tube light

(91) In optical fibre communication, the APD semi conductor divece is ared
(A) to convert radio single into optical single
(B) to obtain intanxty modulayed signal
(C) to covert optical signal into electrical signal
(D) to covert optical signal into electri signal.