UNIT 2 Output devices in complex circuits


In this unit you will learn about: • different kinds of output devices.


Output devices New word


output device – a component in an electrical circuit that changes electrical energy into useful forms of energy


An output device changes electrical energy into useful forms of energy, such as light, sound or movement. For example, a bulb is an output device that produces light. You have worked with simple circuits using a bulb as the output device. More complex circuits use a variety of output devices such as beepers and buzzers, LED (light emitting diodes) and motors.


Light emitting diodes (LEDs)


LEDs are output components that emit light when current flows through them. They are made in three standard colours: green, yellow and red. LEDs do not get hot when current flows through them. This makes them suitable for use as indicators, for example to show whether an appliance is turned on or off.


LEDs are much smaller than normal bulbs. They also use less energy and last longer. They are used in advertising signs, car lighting and traffic signals.


Always make sure that you connect the longer terminal of the LED to the positive terminal of the cell or battery. If you connect it the other way round the LED will not work. If you want to use a LED in a circuit powered by a battery with a voltage higher than 2 V, you must protect it by connecting it in series with a suitable resistor.


Figure 1 LEDs come in many colours 124 Topic 3 Series and parallel circuits


Figure 2 LEDs are used in traffic lights


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