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COMMUNICATIONS - QUESTIONS FROM PREVIOUS CBSE PAPERS |
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Written by Master
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Monday, 09 November 2009 09:45 |
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CBSE VERY SHORT ANSWER TYPE QUESTIONS FROM COMMUNICATION
- What type of modulation is required for television broadcast?
- What type of modulation is required for commercial broadcast of voice signals?
- What should be the frequency of a carrier wave with reference to message signal for the process of modulation?
- Why is the transmission of signals through a coaxial cable not possible for frequencies greater than 20 MHz?
- Why is short wave band used for long distance radiobroadcast?
- Name the types of communication systems according to the mode of transmission.
- Name an appropriate communication channel needed to send a signal of bandwidth 100 kHz over a distance of 8 km.
- What is the function of cladding in a typical optical fibre?
- How does the effective power radiated by an antenna vary with wavelength?
- What is groundwave?
- What is a sky wave?
- Name the type of communication in which the signal is a discrete and binary coded version of the message or information.
- Name the principle on which an optical fibre works.
- Why frequency modulation preferred to amplitude modulation for transmission of music?
- What is the purpose of modulating a signal in transmission?
- What should be the length of dipole antenna for a carrier wave of frequency 5 x 108 Hz?
CBSE SHORT ANSWER QUESTIONS (2 OR 3 MARKS) PREVIOUSLY ASKED IN BOARD EXAMS FROM THE CHAPTER COMMUNICATIONS
- Differentiate an analog signal and a digital signal. How can an analog signal be converted to a digital signal?
- What is meant by modulation? Explain with the help of a block diagram, how the process of modulation is carried out in radio broadcast?
- Write three special characteristics of the light source used in optical communication. Name any one optical detector. Explain the meaning of the term sensitivity of a detector.
- How do we make the choice of a communication channel? A messsage signal has a bandwidth of 5 MHz. Suggest a possible communication channel for its transmission.
- With the help of block diagram explain the working of a modern (fibre optic) communication link.
- The TV transmission tower at a particular station has a height of 160 m. (i) What is the coverage range? (ii) What is the population covered by the transmission, if the average population density around the tower is 1200 km-2?
- By how much should the height of antenna be increased to double the coverage range? Radius of earth is 6400 km.
- Give two main advantages of optical communication. State two special characteristics of (i) light sources and (ii) detector used in optical communication.
- Explain briefly the principle of transmitting signals using a satellite. State two main advantages of using satellite for transmitting signals.
- With the help of a block diagram, explain the principle of an optical communication system. Give its two advantages over cable communication system.
- Why cannot (i) ground waves (ii) space waves and (ii) sky waves be sustained for long distance communication beyond 10 to 20 MHz?
- Explain the following (i) Ground Wave (ii) Sky Wave (iii) Space Wave
- Distinguish between analog and digital communication. Write any two modulation techniques employed for the digital data. Describe briefly one of the techniques used.
- Draw a schematic diagram of a single optical fibre structure. Explain briefly how an optical fibre is fabricated. Describe in brief, the mechanism of propagation of light signal through an optical fibre.
- Explain the need of modulating a low frequency information signal. What is pulse modulation? With the help of diagrams differentiate between PAM and PDM.
- Define the term modulation. Name three different types of modulation used for a message signal using a sinusoidal continuous carrier wave.
- Distinguish between frequency modulation and amplitude modulation. Why is an FM signal less susceptible to noise than an AM signal?
- Name two factors which determine the choice of a communication channel. Explain the use of coaxial cables as a communication channel with the help of a simple diagram.
- What is sky wave propagation of waves? Explain why sky wave transmission of electromagnetic waves cannot be used for TV transmission?
- What do you mean by LOS communication? Name the type of waves that are used for this communication. Which of the two - height of transmitting antenna and height of receiving antenna can affect the range over which the mode of communication remains effective?
- Define the term modulation index for an AM wave. What would be the modulation index for an AM wave for which the maximum amplitude is 'a' while the minimum amplitude is 'b'?
- What is space wave propagation? Which two communication methods make use of this mode of propagation? If the sum of transmitting and receiving antennas be fixed at h, show that the range of transmission is maximum when the two antennae have a height h/2 each.
- Draw a block diagram of a communication system. What is meant by 'detection' of a modulated carrier wave? Describe briefly the essential steps involved in detection.
- A transmitting antenna at the top of tower has a height of 36 m and the height of the receiving antenna is 49 m. What is the maximum distance between them for satisfactory communication in the LOS mode.
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Last Updated on Monday, 09 November 2009 10:42 |
