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Physics · Class 12 Science

Ch 15Communication System — Class 12 Physics, concept-first.

This unit turns from the study of individual electromagnetic and electronic phenomena to a practical question: how is information actually sent from one place to another? A communication system is any arrangement built to carry a message -- speech, music, a picture, or a stream of digital data -- from a sender to one o…

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Key concepts

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Elements of a Communication System

A communication system, regardless of what it carries, is built from three essential blocks connected in a chain: a transmitter, a channel, and a receiver, with noise capable of entering and corrupting the signal at any…

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Chapter contents

The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.

10.1

Introduction

This unit turns from the study of individual electromagnetic and electronic phenomena to a practical question: how is information actually sent from one place to another? A communication system is any…

10.2

Elements of a Communication System

The three elements. Every communication system, however elaborate, is built from exactly three functional blocks, connected in series and shown in this section's block diagram: a transmitter, a channe…

10.3

Need for Modulation

Why modulation is unavoidable. A message signal such as speech (roughly 20 Hz to 20 kHz in principle, though ordinary conversational speech is dominated by a much narrower band) cannot simply be radia…

10.4

Amplitude Modulation

Definition. In amplitude modulation (AM), the amplitude of a high-frequency carrier wave is made to vary in direct proportion to the instantaneous value of a lower-frequency message (modulating) signa…

10.5

Frequency Modulation

Definition. In frequency modulation (FM), it is the carrier's instantaneous frequency, not its amplitude, that is made to vary in proportion to the instantaneous value of the message signal -- the car…

10.6

Bandwidth of Signals

What bandwidth means. The bandwidth of a signal is the width, on the frequency axis, of the band of frequencies that the signal actually contains (or that must be preserved for the signal to be reprod…

10.7

Bandwidth of Transmission Medium

What it means for a medium. Just as a signal has its own bandwidth requirement (Section 10.6), the physical transmission medium carrying it -- a length of cable, or a slice of radio spectrum used for…

10.8

Propagation of Electromagnetic Waves in the Atmosphere

Three ways to reach the receiver. Once a message signal has been modulated onto a carrier and radiated as an electromagnetic wave from a transmitting antenna, it must still physically travel through t…

10.8.1

Ground Wave Propagation

Mechanism. In ground-wave (or surface-wave) propagation, the radiated wave travels close to and essentially along the Earth's surface, its path bending very slightly to follow the curvature of the gro…

10.8.2

Sky Wave Propagation

Mechanism. In sky-wave propagation, the wave is deliberately directed upward, at an angle, toward the ionosphere rather than along the ground.

10.8.3

Space Wave Propagation

Mechanism. At frequencies too high for the ionosphere to reflect (very-high frequency, VHF, and above, roughly above 30 MHz) and too high for the ground wave to carry any meaningful distance, an elect…

Summary

Elements of a communication system: every system is built from a transmitter (prepares and sends the message), a channel (the physical medium, which attenuates and adds noise), and a receiver (recover…

Sample & Board Papers

Sample papers and previous-year board questions for this subject.

+Show 12 questions12 questions
  1. Q1Why is satellite used for TV transmission to far places? **OR** What do you mean by demodulation? What is the importance of modulation index…Preview
  2. Q2Satellite communication is done with (a) ground wave (b) sky wave (c) space wave (d) none of thesePreview
  3. Q3A TV tower is 120 m high. How much more height is to be added to it if its coverage range is to become double? **OR** Draw a neat diagram of…Preview
  4. Q4In communication system, noise is most likely to affect the signal (a) at the transmitter (b) in the transmission medium (c) in the informat…Preview
  5. Q5Draw a labelled block diagram of a communication system.Preview
  6. Q6The process in which the amplitude of the carrier wave is made proportional to the instantaneous amplitude of the signal wave is called (a)…Preview
  7. Q7What is space wave propagation? Why is it limited to small distance over earth's surface? [1+1] **OR** If the highest modulating frequency o…Preview
  8. Q8The electromagnetic waves used in satellite communications are (a) microwaves (b) γ-rays (c) infrared rays (d) UV-raysPreview
  9. Q9The maximum and minimum amplitudes of an amplitude modulated wave are 10 V and 2 V respectively. The magnitude of the modulation index will…Preview
  10. Q10A TV tower is 120 m high. How much more height of the tower is to be increased to it if its coverage range is doubled? **OR** Find the lengt…Preview
  11. Q11The equation of a modulated wave is V = [10 + 4 sin(2πt × 10^3)] sin(2πt × 10^6). What type of modulation is used for the wave? Calculate th…Preview
  12. Q12i) What is an antenna? ii) The height of a TV tower is 80 m. What is the maximum distance from which the signal broadcasted by this tower ca…Preview

More questions

20 Q
+Show 12 questions12 questions
  1. Example 1State and briefly describe, with the help of a block diagram, the three basic elements common to every communication system.Free
  2. Example 2Explain, in the context of a communication system, what is meant by a transducer, a signal, noise, attenuation, amplification and the range…Free
  3. Example 3What is meant by 'modulation'? Why must a low-frequency message signal such as speech be superimposed on a high-frequency carrier wave befor…Free
  4. Example 4Explain briefly why the practical size of a transmitting antenna and the power that antenna can efficiently radiate together make it impossi…Preview
  5. Example 5Describe the principle of amplitude modulation. In particular, explain how the envelope of the modulated carrier wave is related to the orig…Preview
  6. Example 6Define the modulation index of an amplitude-modulated wave and state the condition its value must satisfy for the modulated wave to remain u…Preview
  7. Example 7Describe the principle of frequency modulation and explain, in outline, how a frequency-modulated wave is produced from a message signal and…Preview
  8. Example 8State two important respects in which a frequency-modulated wave differs from an amplitude-modulated wave, and explain qualitatively why FM…Preview
  9. Example 9Explain what is meant by the 'bandwidth' of a signal, and state, with reasons, the approximate bandwidth needed to transmit (i) a telephone-…Preview
  10. Example 10How is the bandwidth required to transmit digital data related to its bit rate? Explain qualitatively why a higher bit rate demands a larger…Preview
  11. Example 11Explain what is meant by the 'bandwidth of a transmission medium', and briefly compare the typical bandwidths available on a twisted-pair ca…Preview
  12. Example 12Explain ground-wave (surface-wave) propagation of an electromagnetic wave. Why is this mode used mainly for low- and medium-frequency broadc…Preview
+Show 8 questions8 questions
  1. Q13Explain sky-wave propagation of an electromagnetic wave. What role does the ionosphere play in it, and what is meant by the 'critical freque…Free
  2. Q14Define 'skip distance' in the context of sky-wave propagation, and explain briefly why short-wave broadcasts can sometimes be received at ve…Free
  3. Q15Explain space-wave propagation and define 'line-of-sight communication'. Why must space-wave (very-high-frequency and above) communication n…Free
  4. Q16A TV transmitting antenna is mounted at the top of a tower of height 175 m. Taking the radius of the Earth as $6.4\times10^{6}$ m, calculate…Preview
  5. Q17The transmitting antenna of a TV tower has a height of 100 m, and the receiving antenna is also raised to a height of 25 m above the ground.…Preview
  6. Q18In an amplitude-modulated wave, the maximum and minimum values of the envelope amplitude are found to be 12 V and 4 V respectively. Calculat…Preview
  7. Q19A sinusoidal message signal of frequency 10 kHz amplitude-modulates a carrier wave. Calculate the bandwidth required to transmit this amplit…Preview
  8. Q20Tabulate and compare the three modes of electromagnetic-wave propagation in the atmosphere -- ground wave, sky wave and space wave -- with r…Preview