Chapter 15 Communication Systems
NCERT Class 12 Physics - Chapter 15: Communication Systems
Topics Covered
- Introduction to Communication Systems
- Elements of a Communication System
- Basic Terminology Used in Electronic Communication Systems
- Bandwidth of Signals
- Bandwidth of Transmission Medium
- Propagation of Electromagnetic Waves
- Modulation and Its Necessity
- Types of Modulation
- Amplitude Modulation (AM)
- Frequency Modulation (FM)
- Phase Modulation (PM)
- Demodulation
- Satellite Communication
- Optical Communication
- Internet
Introduction to Communication Systems
Communication systems are used to transmit information from one place to another. They play a crucial role in modern technology and society.
Example
Television, radio, and mobile phones are examples of communication systems.
Elements of a Communication System
A communication system typically consists of a transmitter, a communication channel, and a receiver.
Example
In a mobile phone call, the caller's phone acts as the transmitter, the cellular network as the communication channel, and the receiver's phone as the receiver.
Basic Terminology Used in Electronic Communication Systems
Key terms include signal, noise, modulation, demodulation, transmitter, receiver, and communication channel.
Example
Signal refers to the information being transmitted, while noise refers to unwanted interference.
Bandwidth of Signals
Bandwidth is the range of frequencies within a given band that a signal occupies. It determines the data rate of the communication system.
Example
A higher bandwidth allows for the transmission of more data, resulting in faster internet speeds.
Bandwidth of Transmission Medium
The transmission medium's bandwidth limits the range of frequencies that can be transmitted. Different media have different bandwidth capacities.
Example
Optical fibers have a much higher bandwidth compared to traditional copper cables.
Propagation of Electromagnetic Waves
Electromagnetic waves can propagate through different mediums such as air, vacuum, and solid materials. The mode of propagation depends on the frequency and the medium.
Example
Radio waves can travel long distances through the atmosphere, while microwaves are used for satellite communication.
Modulation and Its Necessity
Modulation is the process of varying a carrier signal to transmit information. It is necessary to transmit signals over long distances without significant loss or interference.
Example
AM radio uses amplitude modulation to transmit audio signals.
Types of Modulation
There are three main types of modulation: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).
Amplitude Modulation (AM)
In amplitude modulation, the amplitude of the carrier wave is varied in proportion to the information signal.
Example
AM radio stations broadcast audio signals by varying the amplitude of the carrier wave.
Frequency Modulation (FM)
In frequency modulation, the frequency of the carrier wave is varied in proportion to the information signal.
Example
FM radio stations broadcast audio signals by varying the frequency of the carrier wave.
Phase Modulation (PM)
In phase modulation, the phase of the carrier wave is varied in proportion to the information signal.
Example
Phase modulation is used in digital signal processing and telecommunications.
Demodulation
Demodulation is the process of extracting the information signal from the modulated carrier wave. It is the reverse process of modulation.
Example
A radio receiver demodulates the incoming signal to reproduce the original audio signal.
Satellite Communication
Satellite communication uses satellites in orbit to relay signals between distant locations on Earth. It enables global communication and broadcasting.
Example
Satellite TV channels are transmitted via communication satellites.
Optical Communication
Optical communication uses light to transmit information through optical fibers. It offers high bandwidth and low signal attenuation.
Example
Fiber optic internet provides high-speed data transmission using optical fibers.
Internet
The internet is a global network of interconnected computers and communication systems. It enables the exchange of information and access to various online services.
Example
Email, social media, and online streaming are services available through the internet.
Word Meanings
Communication
The process of transmitting information from one place to another.
Transmitter
A device that sends out signals in a communication system.
Receiver
A device that receives signals in a communication system.
Signal
The information being transmitted in a communication system.
Noise
Unwanted interference that affects the transmission of signals.
Modulation
The process of varying a carrier signal to transmit information.
Demodulation
The process of extracting the information signal from a modulated carrier wave.
Bandwidth
The range of frequencies within a given band that a signal occupies.
Carrier Wave
A high-frequency wave that is modulated to carry information.
Amplitude Modulation (AM)
Modulation technique where the amplitude of the carrier wave is varied in proportion to the information signal.
Frequency Modulation (FM)
Modulation technique where the frequency of the carrier wave is varied in proportion to the information signal.
Phase Modulation (PM)
Modulation technique where the phase of the carrier wave is varied in proportion to the information signal.
Satellite
An artificial body placed in orbit around the earth or moon or another planet to collect information or for communication.
Optical Fiber
A flexible, transparent fiber made of glass or plastic, used to transmit light signals.
Internet
A global network of interconnected computers and communication systems.
Propagation
The movement of waves through a medium or space.
Attenuation
The reduction in the strength of a signal as it travels through a medium.
Global Communication
The ability to communicate with people all around the world.
Digital Signal
A signal that represents data as a sequence of discrete values.
Telecommunications
The transmission of information over long distances by electronic means.
FAQs
1. What is a communication system?
A communication system is a system that transmits information from one place to another.
2. What are the basic elements of a communication system?
The basic elements of a communication system are the transmitter, communication channel, and receiver.
3. What is modulation?
Modulation is the process of varying a carrier signal to transmit information.
4. Why is modulation necessary?
Modulation is necessary to transmit signals over long distances without significant loss or interference.
5. What is demodulation?
Demodulation is the process of extracting the information signal from a modulated carrier wave.
6. What is amplitude modulation (AM)?
Amplitude modulation is a modulation technique where the amplitude of the carrier wave is varied in proportion to the information signal.
7. What is frequency modulation (FM)?
Frequency modulation is a modulation technique where the frequency of the carrier wave is varied in proportion to the information signal.
8. What is phase modulation (PM)?
Phase modulation is a modulation technique where the phase of the carrier wave is varied in proportion to the information signal.
9. What is a satellite in communication systems?
A satellite is an artificial body placed in orbit to collect information or for communication purposes.
10. What is optical communication?
Optical communication is the use of light to transmit information through optical fibers.
11. What is the internet?
The internet is a global network of interconnected computers and communication systems.
12. What is the bandwidth of a signal?
The bandwidth of a signal is the range of frequencies within a given band that the signal occupies.
13. What is noise in a communication system?
Noise is unwanted interference that affects the transmission of signals in a communication system.
14. How does a transmitter work?
A transmitter sends out signals in a communication system by converting the information into a form suitable for transmission.
15. How does a receiver work?
A receiver receives signals in a communication system and converts them back into the original information.
16. What is signal attenuation?
Signal attenuation is the reduction in the strength of a signal as it travels through a medium.
17. What is global communication?
Global communication is the ability to communicate with people all around the world.
18. What is a digital signal?
A digital signal represents data as a sequence of discrete values.
19. What is telecommunications?
Telecommunications is the transmission of information over long distances by electronic means.
20. What are some examples of communication systems?
Examples of communication systems include television, radio, mobile phones, and the internet.