CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma
CBSE CLASS XII
Communication System
Q.3) How does the power radiated by an antenna vary with wavelength? (H) ( 1 mark ) (Q.4) What do you mean by bandwidth? ( 1 mark )
(Q.5) Find the length of the dipole antenna for a carrier wave of wavelength λ ? ( 1 mark ) (Q.6) Why is short wave band used for long distance radio broadcast? (1mark ) (Q.7) The power in a transmission line travels ( 1 mark )
(a) inside the conductors
(b) outside the conductors
(c) both inside and outside theconductors
(d) perpendicularly to the surface of the conductors(Q.8) Long distance shoirt-wave radio broad-casting uses ( 1 mark )
(a) Ground wave
(b) Ionospheric wave
(c) Direct wave
(d) Sky wave(Q.10) Given that radius of earth is 6.4 × 106 m and a transmitting antenna at the top of a tower has a height 40 m and the height of the receiving antenna is 50 m. What is the maximum distance between them for satisfactory communication in LOS mode? ( 1 mark )
(a) 45 km
(b) 48 km
(c) 50 km
(d) 57 km(Q.12) At longer wavelengths, the antenna ( 1 mark )
(a) Should have large physical size and located on or very near to the ground
(b) Should have large physical size but far from the ground
(c) Should have small physical size and very near to the ground
(d) Should have small physical size and far from the ground(Q.13) Radio waves of constant amplitude can be generated with ( 1 mark )
(a) Filter
(b) Rectifier
(c) FET
(d) Oscillator(Q.14) The numbers of AM broadcast stations that can be accommodated in a 400 kHz bandwidth for the highest modulating frequency 20 kHz will be (H) ( 1 mark )
(a) 2
(b) 10
(c) 5
(d) 8(Q.16) In a communication system, out of three elements which of the following is the physical medium that connects the other two? ( 1 mark )
(a) Transmitter
(b) Channel
(c) Receiver
(d) Speaker(Q.17) Alternation is ( 1 mark )
(a) Adevice that converts one form of energy into another
(b) Referred to as unwanted signal that disturbs the transmission
(c) The loss of strength of a signal
(d) Adevice which extracts the designed message signals.(Q.18) In communication using radio waves, an antenna at the transmitter radiates which of the following type of wave?(1mark )
(a) Electrical waves
(b) Sound waves
(c) em waves
(d) Radio waves(Q.19) To radiate signals with high efficiency, the antennas should have a size ( 1 mark )
(a) Equal to wavelength 1
(b) Smaller than wavelength 1
(c) Larger than wavelength 1
(d) Comparable to wavelength 1(Q.20) At what height, a peak ionization occurs? ( 1 mark )
(Q.21) The effective power radiated by a long wavelength base band signal would be ( 1 mark )
(a) Small
(b) Large
(c) Comparable
(d) Very small(Q.22) A message signal of frequency 12 kHz and peak voltage of 20 volts is used to modulate a carrier frequency of 2 MHz and peak voltage of 30 volts. Then modulation index is (H) ( 1 mark )
(Q.23) In amplitude modulation ( 1 mark )
(a) μ <= 1
(b) μ >= 1
(c) μ = 1
(d) μ = 0(Q.24) Broadcast frequencies (carrier waves) are sufficiently spaced out so that ( 1 mark )
(a) Sidebands are clear
(b) Sidebands do not overlap
(c) Only one side band will produce
(d) Two side bands only(Q.26) Modulated carrier wave contains the frequencies(H) ( 1 mark )
(a) ωc, ωc+ωm
(b) ωc± ωm
(c) ωc- ωm, ω
(d) ωc , ωc± ωm(Q.27) Many channels get allowed when transmission frequency is ( 1 mark )
(a) Low
(b) High
(c) Very high
(d) Very low(Q.28) With altitude, the electrical conductivity of the earth’s atmosphere ( 1 mark )
(a) Does not change
(b) Decreases
(c) Increase
(d) Does not depend on altitude(Q.29) For ionospheric transmissions, it is desirable to use ( 1 mark )
(a) As high frequency as possible
(b) As low frequency as possible
(c) Not very and not very low frequency
(d) Very low frequency(Q.30) In which frequencies range space waves are normally propagated ( 1 mark )
(a) HF
(b) VHF
(c) UHF
(d) SH(Q.31) Optical fibers are the best medium of transmission over copper wires because ( 1 mark )
(a) The loss of data in optical fibres is large
(b) It is cheap
(c) Easy to construct
(d) The optical fibre can take large number of telephonic message at a time(Q.32) The radio waves of frequency 300 MHz to 3000 MHz belongs to ( 1 mark )
(a) High frequency band
(b) Very high frequency band
(c) Ultra high frequency band
(d) Super high frequency band(Q.33) A transmitting antenna at the top of a tower has a height 32 m and the height of the receiving antenna is 50 m. What is the maximum distance between them for satisfactory communication in LOS mode? (Given radius of earth 6.4x106 m) (H) ( 1 mark )
(a) 35.5 km
(b) 42.5 km
(c) 45.5 km
(d) 10.45 km(Q.34) What is audio frequency range? ( 1 mark )
(a) 20 Hz to 20 kHz
(b) 10 Hz to 10 kHz
(c) 15 Hz to 15 kHz
(d) 30 kHz(Q.35) The length of a half wave dipole at 30 MHz is ( 1 mark )
(a) 10 m
(b) 50 m
(c) 5 m
(d) 100 m(Q.36) Radio waves of constant amplitude can be generated with (H) ( 1 mark )
(a) Filter
(b) Rectifier
(c) FET
(d) Oscillator(Q.37) What should be the length of a dipole antenna for a carrier wave having frequency 3x108 Hz? ( 2 Marks )
(Q.38) What are the four primary constants of a transmission line? ( 2 Marks )
(Q.39) Give two advantages of optical fibre communication? ( 2 Marks )
(Q.40) What is geostationary satellite ? What are its two characteristics? ( 2 Marks )
(Q.42) How would the following be affected in the absence of atmosphere around the earth?( a) Surface temperature of earth.
(b) Range of radio waves transmission.
Give brief explanation in support of your answer. (H) ( 2 Marks )(Q.43) What are the merits and demerits of satellite communication? ( 3 Marks )
(Q.44) What is satellite communication ? Explain its working. ( 3 Marks ) (Q.46) Explain how communication is possible with the help of sky wave propagation? ( 3 Marks )(Q.47) What is amplitude modulation? What is modulation index? Derive the expression for modulation index(H). ( 5 Marks )
Submitted By Mr. Ajay Sharma
Email Id : [email protected]
