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Early experiments with electricity Benjamin Franklin was a scientist in the 18 th century. He carried out many experiments with electricity, including this one. Franklin proved the link between lightning and electricity using a kite attached to a metal key. Don’t try this at home! 3 of 38 © Boardworks Ltd 2008
What is an electrical circuit? An electrical circuit is like a central heating system: l There is a pump that pushes water around the system. l The water everywhere starts to move at the same time. l There are pipes that carry the water. l The water flows through the pipes. 4 of 38 © Boardworks Ltd 2008
What is an electrical circuit? 5 of 38 © Boardworks Ltd 2008
Drawing electrical circuits Scientists don’t draw circuits as they look in real life. This is because it takes too long and each person would draw something slightly different. Instead, they use circuit symbols to represent each component in the circuit. They are drawn exactly the same way each time! Wires are drawn as straight lines. They don’t have to represent the real lengths of the wires. 6 of 38 © Boardworks Ltd 2008
Match the circuit symbols 7 of 38 © Boardworks Ltd 2008
Components in an electrical circuit 8 of 38 © Boardworks Ltd 2008
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What is a series circuit? This is a simple series circuit. In a simple series circuit, everything is connected in one loop across the terminals of the battery. There are no points where the current can split or join (these are called junctions). This circuit has two lamps connected in series. Circuits are always drawn using straight lines. 10 of 38 © Boardworks Ltd 2008
Examples of series circuits Here are some other simple series circuits: 1. Two resistors connected in series. 11 of 38 2. A variable resistor (or rheostat) and a bulb connected in series. © Boardworks Ltd 2008
Measuring current The unit of measurement for current is the amp, which has the symbol A. Current is measured using a device called an ammeter. In a circuit diagram, an ammeter is shown by an ‘A’ in a circle. When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component. 12 of 38 © Boardworks Ltd 2008
Experiment 1: current in a series circuit 13 of 38 © Boardworks Ltd 2008
Current in a series circuit: summary 14 of 38 © Boardworks Ltd 2008
Measuring voltage Voltage is measured using a device called a voltmeter. In a circuit diagram, a voltmeter is given the symbol V. When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. This is still a series circuit, as the voltmeter does not affect the circuit. The voltage supplied by the battery is shared between all the components in a series circuit. 15 of 38 © Boardworks Ltd 2008
Experiment 2: voltage in a series circuit 16 of 38 © Boardworks Ltd 2008
Voltage in a series circuit: summary 17 of 38 © Boardworks Ltd 2008
Current or voltage? 18 of 38 © Boardworks Ltd 2008
Experiment 3: cells in a series circuit 19 of 38 © Boardworks Ltd 2008
Cells in a series circuit: summary 20 of 38 © Boardworks Ltd 2008
Series circuits – key ideas 1. In a series circuit the current is the same in all parts of the circuit. Series circuits are found in torches and strings of Christmas lights. 2. The supply voltage is shared between the components in a series circuit. (The sum of the voltage across each component is the same as the total supply voltage. ) 3. The current depends on the voltage in any circuit. 21 of 38 © Boardworks Ltd 2008
Make your own series circuit 22 of 38 © Boardworks Ltd 2008
Series circuits: summary 23 of 38 © Boardworks Ltd 2008
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What is a parallel circuit? A parallel circuit is one that contains a point (a junction) where the current can split (point A) or join (point B). This means that there is more than one path around the circuit. A 25 of 38 B © Boardworks Ltd 2008
Modelling parallel circuits 26 of 38 © Boardworks Ltd 2008
Measuring current in a parallel circuit 1. Set up the circuit as shown. 2. Place an ammeter, in turn, at positions 1, 2, 3 and 4 and record the readings in a table. Ammeter Current (A) A 1 A 2 A 3 A 4 27 of 38 © Boardworks Ltd 2008
Current in a parallel circuit In a parallel circuit, the current that leaves the cell is the same as the current that returns to the cell. The ammeter readings for A 1 and A 4 should be the same. This is because the current does not get used up by the circuit, just the energy that the current is carrying. 28 of 38 © Boardworks Ltd 2008
Current in a parallel circuit The current splits up at the first junction and then joins together at the second junction. The following is always true for this type of parallel circuit: A 1 = (A 2 + A 3) = A 4 If the bulbs are identical, then the current will split evenly. If the bulbs are not identical, then the current will not split evenly. 29 of 38 © Boardworks Ltd 2008
Measuring voltage in a parallel circuit Connect up this circuit and measure, in turn, the voltage at V 1, V 2 and V 3. Record your results in the table. Voltmeter Voltage (V) V 1 V 2 V 3 What do you notice about the results? How can you explain this? 30 of 38 © Boardworks Ltd 2008
Make your own parallel circuit 31 of 38 © Boardworks Ltd 2008
Cells in a parallel circuit: summary 32 of 38 © Boardworks Ltd 2008
Series and parallel circuits: summary 33 of 38 © Boardworks Ltd 2008
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Glossary 35 of 38 © Boardworks Ltd 2008
Anagrams 36 of 38 © Boardworks Ltd 2008
Multiple-choice quiz 37 of 38 © Boardworks Ltd 2008
True or false? 38 of 38 © Boardworks Ltd 2008
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