Title 15.COMMUNICATION SYSTEMS - Questions.pdf ✅

15.COMMUNICATION SYSTEMS (1.)The characteristic impedance of a co-axial cable is160 Ω. If its inductance is 0.4 mH, its capacitance would be (a.) 15.6 μF (b.) 1.6 F c) 15.6 nF d) 15.6 pF (2.)In amplitude modulation, carrier wave frequencies are (a.) Lower compared to those in frequency modulation (b.) Higher compared to those in frequency modulation c) Same as in frequency modulation d) Lower sometimes and higher sometimes to those in frequency modulation (3.)What type of modulation is employed in India for radio transmission (a.) Amplitude modulation (b.) Frequency modulation c) Pulse modulation d) None of these (4.)In the above question, if oscillator output is modulated by audio frequencies upto 10 kHz, the frequency range occupied by the side bonds will be (a.) 711.9 kHz to 712.1 kHz (b.) 692 kHz to 732 kHz c) 702 kHz to 722 kHz d) 71.2 kHz to 70.2 kHz (5.)If an electromagnetic wave is transmitted to the height equal to 150 km with maximum frequency 300 kHz and critical frequency 100 kHz, the skip distance is (a.) 426 km (b.) 636 km c) 824 km d) 849 km (6.)The diameter of an optical fiber is (a.) 10−5m (b.) 10−4m c) 10−3 cm d) 10−2 cm (7.)The population inversion necessary for laser action used in solid state lasers is (a.) Electrical discharge (b.) Inelastic atom-atom collisions c) Direct conversion d) Optical pumping (8.)What fraction of the surface area of earth can be covered to establish communication by one geostationary satellite? (a.) 1/2 (b.) 1/3 c) 1/4 d) 1/8 (9.)Calculate the phase velocity of electromagnetic wave having electron density and frequency of D- layer, N = 400 electron cc −1 , v = 200 kHz (a.) 3 × 108ms −1 (b.) 3.5 × 108ms −1 c) 6.9 × 108ms −1 d) 1.1 × 109ms −1 (10.)A laser beam of pulse power 1012 W is focused on an object of area10−4 cm2 . the energy flux in Wcm2 at the point of focus is (a.) 1020 (b.) 1016 c) 108 d) 104 (11.)In satellite communication, the communication satellite; (a.) Acts as a reflector for a beam of modulated microwave from transmitter sent directly towards it (b.) Acts as a repeater for a signal reaching there, without any change in frequency c) Receives the coming modulated microwave signal, amplifies it and returns it to earth at a different frequency d) None of the above (12.)The losses in transmission lines are (a.) Radiation losses only (b.) Conductor heating only c) Dielectric heating only d) All of the above (13.)What should be the maximum acceptance angle at the aircore interface of an optical fibre if n1 and n2 are the refractive indices of the core and the cladding, respectively (a.) sin−1 (n2/n1) (b.) sin−1 √n1 2 − n2 2 c) [tan−1 n2 n1 ] d) [tan−1 n1 n2 ] (14.)The space wave propagation is utilized in (a.) Only television communication
(b.) Can be reflected by ionosphere c) Cannot be reflected by mesosphere d) Cannot be reflected by any layer of earth's atmosphere (15.)Ozone layer blocks the radiations of wavelength (a.) Less than 3 × 10−7 m (b.) Equal to 3 × 10−7 m c) More than 3 × 10−7 m d) All of these (16.)The modulation technique used for transforming digital data into analog signals are (a.) Amplitude shift keying (ASK) only (b.) Frequency shift keying (FSK) only c) Phase shift keying (PSK) only d) All of the above (17.)What is the range of the characteristic impedance of a coaxial cable? (a.) Between 150 W to 600 W (b.) Between 50 W to 70 W c) Between 0 W to 50 W d) Between 100 W to 150 W (18.)Advantage of optical fibre is (a.) High band width and EM interference (b.) Low band width and EM interference c) High band width low transmission capacity and no EM interference d) High band width, high data transmission capacity and no EM interference (19.)What should be the velocity of an object so that it’s mass becomes twice of its rest mass? (a.) 3 × 108 ms−1 (b.) 2.59 × 108 ms−1 c) 4 × 108 ms−1 d) None of these (20.)In pulse modulation of analog signals, common pulse system employed are (a.) Pulse amplitude modulation (PAM) (b.) Pulse position and pulse duration modulation (PPM and PDM) c) Pulse code modulation (PCM) d) All of the above (21.)In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frequency will be (a.) 50 cycles/s (b.) 100 cycles/s c) 500 cycles/s d) 50,000 cycles/s (22.)Consider an optical communication system operating at λ~800 nm. Suppose, only 1% of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of 8 kHz (a.) 4.8 × 108 (b.) 48 c) 6.2 × 108 d) 4.8 × 105 (23.)Through which mode of propagation, the radio waves can be sent from one place to another (a.) Ground wave propagation (b.) Sky wave propagation c) Space wave propagation d) All of the above (24.)The fundamental radio antenna is a metal rod which has a length equal to (a.) λ in free space at the frequency of operation (b.) λ/2 in free space at the frequency of operation c) λ/4 in free space at the frequency of operation d) 3λ/4 in free space at the frequency of operation (25.)In optical communication system operating at 1200 nm, only 2% of the source frequency is available for TV transmission having a bandwidth of 5 MHz. The number of TV channels that can be transmitted is (a.) 2 million (b.) 10 million c) 0.1 million d) 1 million (26.)The waves relevant to telecommunications are (a.) Visible light (b.) Infrared c) Ultraviolet d) Microwave (27.)A laser device produces amplification in the (a.) Microwave region (b.) Ultraviolet or visible region c) Infrared region d) None of the above (28.)In which frequencies range space waves normally propagated (a.) HF (b.) VHF c) UHF d) SHF (29.)The electromagnetic waves of frequency 2 MHz to 30 MHz are used (a.) In ground wave propagation (b.) In sky wave propagation c) In microwave propagation d) In satellite communication (30.)Venus looks brighter than other stars, due to (a.) Atomic fusion takes place on its surface (b.) It is closer to the earth than other stars
c) It has higher density than other stars d) It is heavier than other stars (31.)What is the refractive index of the fiber core? (a.) 1.556 (b.) 1.453 c) 1.425 d) 1.626 (32.)Which of the following explain that all galaxies are receding from us? (a.) White dwarfs (b.) Neutron stars c) Black holes d) Red shift (33.)In earth's atmosphere, for E-layer, the virtual height and critical frequency are (a.) 80 km and 3MHz (b.) 90 km and 3.5 MHz c) 120 km and 4.5 MHz d) 110 km and 4 MHz (34.)A laser beam is used for carrying out surgery because it (a.) Is highly monochromatic (b.) Is highly coherent c) Is highly directional d) Can be sharply focused (35.)An antenna is a device (a.) That convert electromagnetic energy into radio frequency signal (b.) That converts radio frequency signal into electromagnetic energy c) That converts guided electromagnetic waves into free space electromagnetic waves and vice- versa d) None of these (36.)The distance of coverage of a transmitting antenna is 12.8 km. Then, the height of the antenna is (Given that radius of earth = 6400 km) (a.) 6.4 m (b.) 12.8 m c) 3.2 m d) 16 m (37.)The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to (a.) h 1/2 (b.) h c) h 3/2 d) h 2 (38.)The velocity factor of a transmission line is x. If dielectric constant of the medium is 2.6, the value of x is (a.) 0.26 (b.) 0.62 c) 2.6 d) 6.2 (39.)The normalised fiber frequency is expressed by (a=fiber core radius, λ0=free space wavelength, μ1, μ2= refractive index of core and cladding) (a.) 2πa λ0 (μ1 2 − μ2 2 ) 2 (b.) 2πa λ0 (μ1 2 − μ2 2 ) 1/2 c) 2πa λ0 (μ1 2 − μ2 2 ) −1/2 d) 2πa λ0 (μ1 2 − μ2 2 ) (40.)The range of characteristics impedance for co- axial wire lines is (a.) 40 Ω to 150 Ω (b.) 400 Ω to 1500 Ω c) 4 Ω to 15 Ω d) 40 kΩ to 150 kΩ (41.)Long distance short-wave radio broadcasting uses (a.) Ground wave (b.) Ionospheric wave c) Direct wave d) Sky wave (42.)The characteristic impedance of a coaxial cable is of the order of (a.) 50 W (b.) 200 W c) 270 W d) None of these (43.)If μ1 and μ2 are the refractive indices of the material of core and cladding of an optical fiber, then the loss of light due to its leakage can be minimised by having (a.) μ1 > μ2 (b.) μ1 < μ2 c) μ1 = μ2 d) None of these (44.)A broken ligament is being ‘welded’ back in place using 20 ms pulses from a 0.5 W laser operating at a wavelength of 632 nm. The number of photons in 5 pulses of laser are (a.) 1.59 × 10−18 (b.) 3.18 × 10−17 c) 1.59 × 1023 d) 3.18 × 10−16 (45.)A laser beam is used for locating distant objects because (a.) It is monochromatic (b.) It is coherent
c) It is not absorbed d) It has small angular speed (46.)The mobile telephones operate typically in the range of (a.) 1 − 100 MHz (b.) 100 − 200 MHz c) 1000 − 2000MHz d) 800 − 950MHz (47.)The velocity of a particle at which the kinetic energy is equal to its rest energy is (a.) ( 3c 2 ) (b.) 3 c √2 c) (3c) 1 2 2 d) c√3 2 (48.)Which of the following is not the main characteristic of laser beam? (a.) High irradiance (b.) High divergence c) Highly monochromatic d) Highly coherent (49.)The frequency band used in the downlink of satellite communication is (a.) 9.5 to 2.5 GHz (b.) 896 to 901 MHz c) 3.7 to 4.2 GHz d) 840 to 935 MHz (50.)The maximum range, dmax of radar is (a.) Proportional to the cube root of the peak transmitted power (b.) Proportional to the fourth root of the peak transmitted power c) Proportional to the square root of the peak transmitted power d) Not related to the peak transmitted power at all (51.)Flash spectrum confirms a/an (a.) Magnetic stom (b.) Earthquake c) Lunar eclipse d) Total solar eclipse (52.)The ratio waves of frequency 30 MHz to 300 MHz belong to (a.) High frequency band (b.) Very high frequency band c) Ultra high frequency band d) Super high frequency band (53.)In earth's atmosphere, for F1-layer; the virtual height and critical frequency are (a.) 150 km and 3 MHz (b.) 160 km and 3.5 MHz c) 170 km and 4.5 MHz d) 180 km and 5 MHz (54.)Special theory of relativity states that (a.) Mass remains unaffected in any inertial frame (b.) Velocity of light remains unaffected in any inertial frame c) Time remains same in all inertial frames d) None of the above (55.)If a radio receiver amplifies all the signal frequencies equally well, it is said to have high (a.) Fidelity (b.) Distortion c) Sensibility d) Sensitivity (56.)For good demodulation of AM signal of carrier frequency f, the value of RC should be (a.) RC = 1 f (b.) RC < 1 f c) RC ≥ 1 f d) RC >> 1 f (57.)The relation between the maximum electron density Nmax and the critical frequency fc for the ionosphere can be given as (a.) fc = √9 Nmax (b.) fc = √9 Nmax c) fc = 9√ Nmax d) None of these (58.)Antenna is (a.) Inductive (b.) Capacitive c) Resistive above its resonant frequency d) Resistive at resonant frequency (59.)If fa and ff represent the carrier wave frequencies for amplitude and frequency modulations respectively, then (a.) fa > ff (b.) fa < ff c) fa = ff d) fa ≥ ff (60.)You are using light of wavelength 1400 nm in a photodetector. Which of the following semiconductor is to be used having band gap as? (h = 6.63 × 10−34Js; c = 3 × 108ms −1 ) (a.) 1eV (b.) 2eV c) 3eV d) 3.5eV (61.)In a communication system, noise is most likely to affect the signal (a.) At the transmitter (b.) In the channel or in the transmission line c) In the information source d) At the receiver (62.)Which of the following is correct?