Chapter 3 — Electricity: Circuits and Their Components

Chapter 3, 'Electricity: Circuits and their Components', introduces students to the basic components of an electrical circuit — electric cells, batteries, incandescent lamps, LED lamps, switches, and wires — and explains how current flows through a complete circuit. It also covers conductors and insulators and how to draw circuit diagrams.

An electric cell is a portable source of electrical energy. It has two terminals: the positive (+ve) terminal, which is the small protruding metal cap, and the negative (–ve) terminal, which is the flat metal disc on the other side.

A battery is a combination of two or more cells connected so that the positive terminal of one cell is connected to the negative terminal of the next. Connecting more than one cell provides energy to the circuit for a longer time and/or more energy. (Note: the term 'battery' is also commonly used for a single cell, such as the one that powers a mobile phone.)

The filament is a thin wire inside the glass bulb of an incandescent lamp. When electric current passes through it, the filament gets hot and glows to produce light. If the filament breaks, the lamp 'fuses' and stops glowing because the broken filament stops the flow of current.

An incandescent lamp has a filament that heats up and glows when current passes through it; current can flow through it regardless of which terminal connects to positive or negative. An LED (Light Emitting Diode) has no filament, and current can pass through it in one direction only — its positive terminal (longer wire) must connect to the positive terminal of the battery, and its negative terminal (shorter wire) to the negative terminal.

Current can pass through an LED in one direction only. The LED glows only when its positive terminal (the longer wire) is connected to the positive terminal of the battery and its negative terminal (the shorter wire) is connected to the negative terminal. Reversing the connections blocks current flow and the LED does not glow.

An electrical circuit is a setup that provides a complete path for electric current to flow. A lamp glows only when one terminal of the lamp is connected to one terminal of the electric cell and the other terminal of the lamp to the other terminal of the cell, forming a complete circuit. If the circuit is broken anywhere, current stops and the lamp does not glow.

A switch is a simple device that either completes or breaks a circuit. In the ON position the circuit is closed and current flows, making the lamp glow. In the OFF position there is a gap in the circuit that prevents current flow and the lamp does not glow. A switch can be placed anywhere in a circuit.

A circuit diagram is a representation of an electrical circuit using standard symbols for components such as cells, batteries, lamps, LEDs, switches, and wires. Using symbols makes it easier to draw and understand circuits. International organisations like IEC, ANSI, and IEEE create these standard symbols so people from different countries and industries can understand each other easily.

Conductors are materials through which electric current can flow easily — metals are conductors, and silver, copper, and gold are the best. Insulators are materials through which current cannot pass, such as rubber, plastic, ceramics, wood, glass, and wax. Copper is used for electrical wires because of its lower cost and abundant supply, while insulators like rubber and plastic are used to coat wires and protect people from electric shocks.

Rubber and plastic are electrical insulators — current cannot pass through them. Wires are covered with these materials to protect people from electric shocks, since our body is a conductor of electricity and electric current passing through it can cause severe injury or even death.

Electricity from batteries is called Direct Current (DC) and usually powers small devices. The electricity from power plants that comes to wall sockets is called Alternating Current (AC) and can run larger appliances.

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