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Electrical Circuits 1 of 10 © Boardworks Ltd 2015 What is an electric circuit? An electric circuit is a path for electric charge to flow along. Like all electrical devices, this portable MP3 player contains electric circuits to enable it to play music. What is needed for an electric circuit to work? source of energy a complete loop a component no short circuits 2 of 10 © Boardworks Ltd 2015 How are wires shown in circuit diagrams? Wires or leads are used to carry the current around a circuit between the components. They are usually made from thin copper wires twisted together and covered with a plastic sleeve. circuit symbol for a wire Circuit diagrams can be complex and it is important to be able to distinguish between wires that are joined together and those that cross without being joined. two wires that are connected 3 of 10 two wires that cross (i.e. not connected) © Boardworks Ltd 2015 What is the source of energy in a circuit? Mains electricity is often used to power electric circuits. When mains electricity is unsuitable, cells or batteries can be used as the source of electrical energy. This remote control uses batteries. Circuit symbol for a cell Circuit symbol for a battery 4 of 10 V © Boardworks Ltd 2015 Circuit components 5 of 10 © Boardworks Ltd 2015 Which circuit diagram? 6 of 10 © Boardworks Ltd 2015 What is current? Current is a measure of the rate of flow of electric charge in a circuit. Electric charge is measured in coulombs. Current is measured in amperes (A) using an ammeter. It is calculated using the equation: A current = charge time or I = Q t A current of 1 A is 1 coulomb of charge flowing every second. So, a current of 5 A is 5 coulombs of charge flowing every second. 7 of 10 An ammeter must be connected in series as it measures the current flowing through it. © Boardworks Ltd 2015 What is potential difference? Potential difference is the work done (or energy transferred) between two points in a circuit, per coulomb of charge. Potential difference is also called voltage. Voltage is measured in volts (V) using a voltmeter. voltage = work done or V = W charge Q A 1 V cell gives 1 joule (J) of energy to each coulomb of charge. V A voltmeter must be connected in parallel So, a 12 V battery gives 12 J of as it measures the energy to each coulomb of charge. potential difference The voltage of a battery is the “push” across the component. it gives the charges in the circuit. 8 of 10 © Boardworks Ltd 2015 How can battery voltage be increased? Using more cells in a battery increases the voltage. If several cells are connected in series, the total voltage across the battery can be found by adding the voltages of the cells. So, if 2 cells with a voltage of 1.5 V are connected together, the voltage across the battery is 3 V. When three cells of 1.5 V are connected, what is the voltage across the battery? 9 of 10 1.5 V V 3V V 4.5 V V © Boardworks Ltd 2015 Current and voltage – true or false? 10 of 10 © Boardworks Ltd 2015