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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 15 COMMUNICATION SYSTEMS

Communication systems

Block diagram of communication system

Modes of communication

Point-to-point communication

Point to multipoint communication-broadcast

Terms related to communication

Transmitter

Receiver

Communication channel

Transducer

Attenuation

Amplification

Repeater

Range of communication

Bandwidth

Bandwidth of some media types

Some wireless frequency bands

Different types of signals

Electrical signal

Noise signal

Analog signal

Digital signal

Coding systems

Rectangular waves

Role of atmosphere in propagation of electromagnetic waves

Different types of waves used in communication

Ground waves

Sky waves

Space waves

Modulation

Demodulation

Baseband signal

Need for modulation

How does size of the antenna related to the frequency of transmitted wave?

How is the effective power radiated by an antenna related to the frequency of transmitted wave?

How does mixing up of signals from different transmitters make modulation necessary?

Mechanism of modulation

Sinusoidal carrier

Pulsed shaped carrier

Amplitude modulation

Modulation index

Side bands

Production and transmission of amplitude modulated wave

Band pass filter

Detection of amplitude modulated wave

Internet

Main applications of Internet

Facsimile (FAX)

Mobile telephony

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 15 COMMUNICATION SYSTEMS

The Internet

It is an interconnection of billions of (users) systems worldwide. It permits communication and sharing of all types of information between any two or more computers connected through a large and complex network. It was started in 1960’s and opened for public use in 1990’s.

Main applications of Internet

  1. E mail – It permits exchange of text/graphic material using email software. We can write a letter and send it to the recipient through ISP’s (Internet Service Providers) who work like the dispatching and receiving post offices.

  2. File transfer – FTP (File Transfer Protocol) allows transfer of files/software from one computer to another connected to the Internet.

  3. World Wide Web (WWW) – Computers that store specific information for sharing with others provide websites either directly or through web service providers. Government departments, companies, NGO’s (Non-Government Organisations) and individuals can post information about their activities for restricted or free use on their websites. This information becomes accessible to the users. Several search engines like Google, Yahoo! etc. help us in finding information by listing the related websites.

  4. Hypertext is a powerful feature of the web that automatically links relevant information from one page on the web to another using HTML (hypertext markup language).

  5. E-commerce – Use of the Internet to promote business using electronic means such as using credit cards is called E-commerce. Customers view images and receive all the information about various products or services of companies through their websites. They can do on-line shopping from home/office. Goods are dispatched or services are provided by the company through mail/courier.

  6. Chat – Real time conversation among people with common interests through typed messages is called chat. Everyone belonging to the chat group gets the message instantaneously and can respond rapidly.
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