Information and communication technology: Class 10 Physics

Key points

Information is meaningful data such as a message, a picture or a sound. Communication is the transfer of information from a sender to a receiver. Information and communication technology (ICT) is the use of electronic devices, networks and software to collect, store, process and send information. It includes telephones, radio, television, computers, mobile phones and the internet.

Parts of a communication system:

• Transmitter (sender): changes the message into a signal suitable for sending.
• Channel (medium): the path along which the signal travels, such as a wire, optical fibre or air.
• Receiver: collects the signal and changes it back into the message.
• Noise: unwanted signals that disturb the message in the channel.

A signal can be analogue or digital. An analogue signal changes continuously and can take any value in a range. A digital signal has only two levels, 1 and 0. Digital signals resist noise better, can be stored and processed by computers, and can be sent again by repeaters without loss of quality. Speech from a microphone is converted to digital form by sampling it many times per second and writing each sample as a binary number.

Transmission media:

• Twisted pair cable: two insulated copper wires twisted together. It is cheap and used in telephone lines and local networks.
• Coaxial cable: a copper core with an insulator and a metal shield. It carries higher frequencies and is used for cable television.
• Optical fibre: a thin glass strand that carries pulses of light by total internal reflection. It has a very high data capacity, low loss and no electrical interference.
• Wireless media: radio waves, microwaves and infrared pass through air or space without any cable.

Radio and other electromagnetic waves travel at the speed of light, c = 3 × 10⁸ m/s, in air or vacuum. They obey v = f λ. Radio waves have the longest wavelengths in the electromagnetic spectrum. Long waves follow the ground, and medium and short waves are reflected by the ionosphere, so they can reach distant places. Very high frequency waves, such as FM radio, TV and mobile signals, pass through the ionosphere and need a line of sight. Microwaves are used for satellite links and radar.

The human voice has a low frequency and cannot travel far by itself. To send it, a high frequency radio wave called the carrier is used. Modulation is the process of making the carrier carry the message. In amplitude modulation (AM) the amplitude of the carrier changes in step with the message while the frequency stays fixed. In frequency modulation (FM) the frequency of the carrier changes while the amplitude stays fixed. FM is less affected by noise and gives better sound quality, while AM signals can travel farther. At the receiver, demodulation separates the message from the carrier.

A mobile phone network divides the area into regions called cells. Each cell has a base station with an antenna. The phone sends radio signals to the nearest base station, which connects the call through the network. As the user moves, the call is handed over from one cell to the next. Because the same frequencies can be reused in cells that are far apart, many people can use the network at once.

A communication satellite orbits the Earth and relays signals. A geostationary satellite orbits above the equator at a height of about 36 000 km and takes 24 hours for one orbit, the same as the Earth's rotation, so it stays above the same place. It receives a signal from one station (uplink), amplifies it and sends it back to Earth (downlink) at a different frequency. Satellites carry television, telephone and internet links over long distances. The Global Positioning System (GPS) uses a group of satellites that send time signals, and a receiver on Earth uses the signals from several satellites to find its position.

The internet is a worldwide network of connected computer networks. It uses common rules called protocols to send data in small packets. Each device has an address. Common internet services are the World Wide Web, e-mail, video calls, online learning and online banking. A web browser is software that displays web pages. A search engine helps find information. Users should protect accounts with strong passwords, avoid sharing private details and use trusted websites.

The speed at which data is sent is the data rate, measured in bits per second (bps), or in kilobits (kbps), megabits (Mbps) and gigabits (Gbps) per second. One byte is 8 bits. A file of size S bytes sent at data rate R bits per second takes t = 8 S / R seconds. Bandwidth is the range of frequencies a channel can carry, and a wider bandwidth allows a higher data rate. Optical fibre has a far larger bandwidth than copper cable.

ICT has made life easier through online education, e-commerce, telemedicine, e-government and remote work. It also brings problems such as hacking, spreading of false information, loss of privacy and too much screen time. Responsible use of technology and good security habits are important for every user.

Study tip: Make a short table of transmission media with one use of each, and one for AM and FM. In numericals convert prefixes (kilo, mega, giga) first and keep c = 3 × 10⁸ m/s. For long answers on satellites or mobile phones, draw a simple block diagram with labels and then explain it in three or four short steps.

Definitions and flashcards

Say the meaning first, then open the card to check.

Formula sheet

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Short questions with model answers

These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.

Numericals with worked steps

Common mistakes

• Confusing bits and bytes. 1 byte = 8 bits, and speeds are quoted in bits per second.
• Forgetting to change MHz and kHz to Hz before using c = f λ.
• Mixing AM and FM. In AM the amplitude changes, in FM the frequency changes.
• Saying that a geostationary satellite is fixed in space. It is fixed over one point of the Earth because it moves with the Earth's rotation.
• Treating the internet and the World Wide Web as the same thing. The web is one service on the internet.

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