TOPIC 2


Energy transfer in electrical systems UNIT 1 Circuits and current electricity In this unit you will learn about:


• how an electric circuit works. • the components of a circuit.


LET US CHECK ✔ An electrical circuit is a system that transfers electrical energy.


New words


current – the move- ment of charge in an electric circuit


complete circuit – a circuit in which electricity can flow in a continuous unbroken pathway


filament – a very thin metal wire found in some light bulbs


incandescent – gives off light when heated


Current electricity and complete circuits Current electricity is different to static electricity. With current electricity, the charges do not stay still but flow through an electrical circuit. The flow of electric charges is called a current. In Grade 6 you found out that a complete circuit is needed to make a device in the circuit, such as a light bulb, light up. A complete (closed) circuit is one in which there are no breaks in the circuit and the electricity can flow in a continuous pathway around the circuit. A circuit is a complete conducting path along which the current can flow.


A circuit has a number of components connected together to make it work. We can describe the flow of the electric current along a pathway like this:


light bulb


positive terminal


battery


negative terminal


conducting wire


1 The electric current flows from the positive terminal.


2 The current flows along metal conducting wire.


3 The electricity goes through an output device such as the metal filaments of an incandescent light bulb.


4 The current flows back to the other terminal of the cell or battery.


Figure 1 The circuit is complete, so the bulb lights up 106 Topic 2 Energy transfer in electrical systems


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