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# 7 j electrical circuits (boardworks)

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### 7 j electrical circuits (boardworks)

1. 1. KS3 Physics 7J Electrical Circuits 1 of 41 20 © Boardworks Ltd 2004 2005
2. 2. Contents 7J Electrical Circuits Introducing circuits Series circuits Parallel circuits Energy in circuits Summary activities 1 of 41 20 2 © Boardworks Ltd 2004 2005
3. 3. What is an electrical circuit? An electrical circuit is like a central heating system in a house. There is a pump that pushes water around the system. The water everywhere starts to move at the same time. There are pipes that carry the water. In the pipes the water is flowing. 1 of 41 20 3 low pressure boiler and pump high pressure radiator radiator flow of water © Boardworks Ltd 2004 2005
4. 4. What is an electrical circuit? The bulb in the circuit is like a radiator. An electrical device uses electrical energy supplied by the circuit. Instead of a flow of water, electricity flows in an electrical circuit. The wires are like pipes; they carry the flow of electricity (called current) around the circuit. The electrical current is pushed by the cell (or battery), which has the same function as the pump and boiler. The strength of push provided by the battery is called its voltage. 1 of 41 20 4 © Boardworks Ltd 2004 2005
5. 5. Components in an electrical circuit 1 of 41 20 5 © Boardworks Ltd 2004 2005
6. 6. Contents 7J Electrical Circuits Introducing circuits Series circuits Parallel circuits Energy in circuits Summary activities 1 of 41 20 6 © Boardworks Ltd 2004 2005
7. 7. 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. So there aren’t any 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. 1 of 41 20 7 © Boardworks Ltd 2004 2005
8. 8. Examples of series circuits Here are some other simple series circuits: 1. Two resistances (resistors) connected in series: R1 R2 2. A rheostat (or variable resistor) and a bulb connected in series: 1 of 41 20 8 © Boardworks Ltd 2004 2005
9. 9. Measuring current The unit of measure 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 the symbol A . When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component. A 1 of 41 20 9 © Boardworks Ltd 2004 2005
10. 10. Experiment 1: Current in series circuit Circuit 1 1 A R1 A 2 1. Set up the circuit as shown above. 2. Measure the current using the ammeter at positions 1 and 2. 1 of 20 10 of 41 © Boardworks Ltd 2004 2005
11. 11. Experiment 1: Current in a series circuit Circuit 2 1 A A R1 A 3 R2 2 1. Add another resistor into the circuit (R2) and another ammeter after it. 2. Now measure the current using the ammeter at positions 1, 2 and 3. 1 of 20 11 of 41 © Boardworks Ltd 2004 2005
12. 12. Experiment 1: Current in a series circuit – results Circuit 1 1 Circuit 2 A 1 R1 A 2 A A 3 R1 A 2 R2 Circuit 1 results: Circuit 2 results: Current at position 1 = Current at position 1 = Current at position 2 = Current at position 2 = Current at position 3 = 1 of 20 12 of 41 © Boardworks Ltd 2004 2005
13. 13. Experiment 1: Current in a series circuit – summary Circuit 1 Circuit 2 A A R1 A A R1 A R2 Circuit 1 The current at different positions in the circuit, before and after the resistor, was the _______. Current is _____ used up by the components in the circuit. Circuit 2 Increasing the number of components in the circuit ________ the current. The current at all points in a series circuit is the _______. same / same / decreased / not 1 of 20 13 of 41 © Boardworks Ltd 2004 2005
14. 14. 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. V1 This is still a series circuit. V2 V3 The voltage supplied by the battery is shared between all the components in a series circuit. 1 of 20 14 of 41 © Boardworks Ltd 2004 2005
15. 15. Measuring voltage across a resistance or a bulb Voltage is measured by connecting the voltmeter across (or in parallel with) the component. V Voltage is measured in volts and the symbol for this is V. A Components component here R V 1 of 20 15 of 41 © Boardworks Ltd 2004 2005
16. 16. Experiment 2: Voltage in a series circuit Circuit 1 V R1 V 1. Set up the circuit as shown above. 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. 3. Then connect the voltmeter across the resistance (R) and measure this voltage. 1 of 20 16 of 41 © Boardworks Ltd 2004 2005
17. 17. Experiment 2: Voltage in a series circuit Circuit 2 V R1 R2 V1 V2 1. Add another resistor (R2) to the circuit as shown. 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. 3. Then measure the voltage across each of the resistor. 1 of 20 17 of 41 © Boardworks Ltd 2004 2005
18. 18. Experiment 2: Voltage in a series circuit – results Circuit 1 Circuit 2 V V R1 R1 R2 V V1 V2 Circuit 2 results: Circuit 1 results: Voltage (supply) = Voltage (supply) = V Voltage (R1) V Voltage (R1) = V Voltage (R2) 1 of 20 18 of 41 V = V = © Boardworks Ltd 2004 2005
19. 19. Experiment 2: Voltage in a series circuit – summary Circuit 1 V Circuit 2 V R R1 R2 V V1 V2 The current is the _______ of electricity around the circuit. The _________ is the amount of push. When two components were put into Circuit 2, the voltage of the supply was the _______ as Circuit 1. However, the voltage across R1 __________ . The voltage across both components in Circuit 2 added to be equal to the ________ voltage. supply / decreased / voltage / flow / same 1 of 20 19 of 41 © Boardworks Ltd 2004 2005
20. 20. Experiment 3: Cells in a series circuit Circuit 1 V R A V 1. Set up the circuit as shown above. 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. Then measure the voltage across the resistance. Also measure the current. 1 of 20 20 of 41 © Boardworks Ltd 2004 2005
21. 21. Experiment 3: Cells in a series circuit Circuit 2 V R A V 1. Add an additional battery to the circuit. 2. Connect the voltmeter across the power supply and measure the supply voltage. Then measure the voltage across the resistance. Also measure the current. 1 of 20 21 of 41 © Boardworks Ltd 2004 2005
22. 22. Experiment 3: Cells in a series circuit – results Circuit 1 R V A V Circuit 2 R V A V Circuit 1 results: Supply voltage = Supply voltage = Voltage R = Voltage R = Current = 1 of 20 22 of 41 Circuit 2 results: Current = © Boardworks Ltd 2004 2005
23. 23. Experiment 3: Cells in a series circuit – summary Circuit 1 R V A V Circuit 2 R V A V Delete the wrong answer: Increasing the number of cells increases/decreases the current that flows in the circuit. The current/voltage depends on the current/voltage. 1 of 20 23 of 41 © Boardworks Ltd 2004 2005
24. 24. Series circuits – key ideas 1. In a series circuit the current is the same in all parts of the circuit. 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. 1 of 20 24 of 41 © Boardworks Ltd 2004 2005
25. 25. Make your own series circuit 1 of 20 25 of 41 © Boardworks Ltd 2004 2005
26. 26. Contents 7J Electrical Circuits Introducing circuits Series circuits Parallel circuits Energy in circuits Summary activities 1 of 20 26 of 41 © Boardworks Ltd 2004 2005
27. 27. What is a parallel circuit? A parallel circuit is one which 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 1 of 20 27 of 41 B © Boardworks Ltd 2004 2005
28. 28. Measuring current in a parallel circuit 1. Place the ammeter, in turn, at positions 1, 2, 3 and 4. A1 A2 A4 A3 2. Record the ammeter readings in the table. Ammeter Current (A) A1 A2 A3 A4 1 of 20 28 of 41 © Boardworks Ltd 2004 2005
29. 29. Current in a parallel circuit For a parallel circuit, the current that leaves the cell is the same as the current that returns to the cell. A1 A2 A4 A1 = A4 A3 The current does not get used up by the circuit, just the energy that the electrons are carrying. 1 of 20 29 of 41 © Boardworks Ltd 2004 2005
30. 30. Current in a parallel circuit The current splits up at the first junction and then joins together at the second junction. A1 A2 A3 A4 The following is always true for this type of parallel circuit: A1 = (A2 + A3) = A4 If the bulbs are identical then the current will split evenly. If the bulbs are not identical, then the current will not split evenly. 1 of 20 30 of 41 © Boardworks Ltd 2004 2005
31. 31. Measuring voltage in a parallel circuit Connect up this circuit and measure, in turn, the voltage at V1, V2 and V3. Record your results in the table. V1 Voltmeter V2 Voltage(V) V1 V2 V3 V3 What do you notice about the results? How can you explain this? 1 of 20 31 of 41 © Boardworks Ltd 2004 2005
32. 32. Make your own parallel circuit 1 of 20 32 of 41 © Boardworks Ltd 2004 2005
33. 33. Contents 7J Electrical Circuits Introducing circuits Series circuits Parallel circuits Energy in circuits Summary activities 1 of 20 33 of 41 © Boardworks Ltd 2004 2005
34. 34. Energy transfer in circuits Energy cannot be created or destroyed. In all devices and machines, including electric circuits, energy is transferred from one type to another. When this circuit is connected, chemical energy stored in the battery is transferred via electrical energy to heat and light energy in the bulbs. The total amount of heat and light energy is the same as the amount of chemical energy lost from the battery. 1 of 20 34 of 41 © Boardworks Ltd 2004 2005
35. 35. Energy transfer in electrical circuits 5 J transferred to bulb as light energy chemical energy from battery (e.g. 100J) 95 J transferred to heat energy of bulb Most of the energy from the battery does not produce light – most of it is wasted as heat! 1 of 20 35 of 41 © Boardworks Ltd 2004 2005
36. 36. What’s the energy transfer? Batteries can power many electrical devices. What sort of energy is electrical energy transferred into in these electrical devices? 1 of 20 36 of 41 © Boardworks Ltd 2004 2005
37. 37. Contents 7J Electrical Circuits Introducing circuits Series circuits Parallel circuits Energy in circuits Summary activities 1 of 20 37 of 41 © Boardworks Ltd 2004 2005
38. 38. Glossary ammeter – A device that measures electric current. circuit – A complete loop of conducting components that electricity flows around. current – The flow of electricity, measured in amps (A). parallel – A branched circuit – it has components connected on separate branches. resistor – A component that makes it difficult for electricity to flow and so reduces the current. series – A circuit without any branches – it has components connected in a row. voltage – The amount of ‘push’ that a cell gives a circuit, measured in volts (V). voltage – A device that measures voltage. 1 of 20 38 of 41 © Boardworks Ltd 2004 2005
39. 39. Anagrams 1 of 20 39 of 41 © Boardworks Ltd 2004 2005
40. 40. Compare a series and a parallel circuit 1 of 20 40 of 41 © Boardworks Ltd 2004 2005
41. 41. Multiple-choice quiz 1 of 20 41 of 41 © Boardworks Ltd 2004 2005