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Electricity Distribution 1 of 9 © Boardworks Ltd 2015 What is a transformer? The voltage of an alternating current can be changed using a device called a transformer. A transformer contains two coils that are wound around a soft iron core. iron core The alternating current in the primary (input) coil produces an alternating magnetic field. This alternating magnetic field induces an alternating current in the secondary (output) coil. 2 of 9 primary coil secondary coil © Boardworks Ltd 2015 How does a transformer change voltage? The voltage induced in the secondary (output) coil depends on the number of turns on the primary and secondary coils. A step-up transformer has more turns on the secondary coil and so increases voltage. 3 of 9 A step-down transformer has fewer turns on the secondary coil and so decreases voltage. © Boardworks Ltd 2015 Transformer power Transformers not only change voltage; they also change current. If the voltage increases, such as in a step-up transformer, the current decreases. This is because for any transformer: power in = power out And because: power = voltage × current If the voltage increases, the current must decrease to ensure that power out remains the same as power in. 4 of 9 © Boardworks Ltd 2015 Why use high voltages for distribution? 5 of 9 © Boardworks Ltd 2015 Example uses for transformers Step-up transformers are mainly used in power transmission to increase voltage to reduce energy loss. Some household appliances (such as older style CRT TVs) also increase voltages using step-up transformers. Step-down transformers are used in electricity substations to reduce the voltage to 230 V for domestic use. Appliances generally reduce this again, as most electronic circuits use 5–12 V. 6 of 9 © Boardworks Ltd 2015 Transformers and the supply chain 7 of 9 © Boardworks Ltd 2015 The electricity supply chain 8 of 9 © Boardworks Ltd 2015 Want to see more? This is only a sample of one of thousands of Boardworks Science presentations. To see more of what Boardworks can offer, order a full presentation completely free: www.boardworks.co.uk/sciencepresentation 9 of 9 © Boardworks Ltd 2015