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9 i energy & electricity (boardworks)

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  • 1. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20051 of 34 KS3 Physics 9I Energy and Electricity
  • 2. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20052 of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities
  • 3. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20053 of 34 The unit of measure for current is the amp, which has the symbol A. A Measuring current AA Current is measured using a device called an ammeter. In a circuit diagram, an ammeter is shown by the symbol . When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component.
  • 4. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20054 of 34 1 2 1. Set up the circuit as shown above. R1 A A Experiment 1: Current in series circuit Circuit 1 2. Measure the current using the ammeter at positions 1 and 2.
  • 5. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20055 of 34 3 1. Add another resistor into the circuit (R2) and another ammeter after it. R1 A A A R2 Experiment 1: Current in a series circuit Circuit 2 1 2 2. Now measure the current using the ammeter at positions 1, 2 and 3.
  • 6. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20056 of 34 Circuit 2 results: Current at position 1 = Current at position 2 = Current at position 3 = Circuit 1 results: Current at position 1 = Current at position 2 = Experiment 1: Current in a series circuit – results R1 A A Circuit 1 Circuit 2 R1 R2 A A A1 2 1 2 3
  • 7. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20057 of 34 Experiment1:Current in a series circuit–summary 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 Circuit 1 Circuit 2 R1 A A R1 R2 A A A
  • 8. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20058 of 34 What is a parallel circuit? A B This means that there is more than one path around the circuit. A parallel circuit is one which contains a point (a junction) where the current can split (point A) or join (point B).
  • 9. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 20059 of 34 A1 A2 A3 A4 1. Place the ammeter, in turn, at positions 1, 2, 3 and 4. Measuring current in a parallel circuit Ammeter Current (A) A1 A2 A3 A4 2. Record the ammeter readings in the table.
  • 10. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200510 of 34 For a parallel circuit, the current that leaves the cell is the same as the current that returns to the cell. Current in a parallel circuit The current does not get used up by the circuit, just the energy that the electrons are carrying. A1 A2 A3 A4 A1 = A4
  • 11. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200511 of 34 The current splits up at the first junction and then joins together at the second junction. Current in a parallel circuit If the bulbs are identical then the current will split evenly. The following is always true for this type of parallel circuit:A1 A2 A3 A4 A1 = (A2 + A3) = A4 If the bulbs are not identical, then the current will not split evenly.
  • 12. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200512 of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities
  • 13. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200513 of 34 When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. Voltage is the amount of push and is measured in ‘volts’ which has the symbol V. This is still a series circuit. Measuring voltage The voltage supplied by the battery is shared between all the components in a series circuit. V3 V2 V1 V Voltage is measured using a device called a voltmeter. In a circuit diagram, a voltmeter is given the symbol .
  • 14. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200514 of 34 1. Set up the circuit as shown above. R1 V V Circuit 1 Experiment 2: Voltage in a series circuit 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.
  • 15. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200515 of 34 1. Add another resistor (R2) to the circuit as shown. V2 Experiment 2: Voltage in a series circuit Circuit 2 R1 R2 V V1 2. Connect the voltmeter across the power supply (battery) and measure the supply voltage. 3. Then measure the voltage across each of the resistor.
  • 16. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200516 of 34 Circuit 1 results: Voltage (supply) = V Voltage (R1) = V R1 R2 V V1 V2 R1 V V Circuit 1 Circuit 2 Experiment 2: Voltage in a series circuit – results Circuit 2 results: Voltage (supply) = V Voltage (R1) = V Voltage (R2) = V
  • 17. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200517 of 34 Experiment 2:Voltage in a series circuit–summary 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. R1 R2 V V1 V2 R V V Circuit 1 Circuit 2 supply / decreased / voltage / flow / same
  • 18. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200518 of 34 Make your own series circuit
  • 19. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200519 of 34 V2 Connect up this circuit and measure, in turn, the voltage at V1, V2 and V3. Record your results in the table. Measuring voltage in a parallel circuit What do you notice about the results? How can you explain this? Voltmeter Voltage(V) V1 V2 V3 V1 V3
  • 20. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200520 of 34 Make your own parallel circuit
  • 21. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200521 of 34 1. Set up the circuit as shown above. V V R A Experiment 3: Cells in a series circuit Circuit 1 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.
  • 22. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200522 of 34 1. Add an additional battery to the circuit. V V R A Experiment 3: Cells in a series circuit Circuit 2 2. Connect the voltmeter across the power supply and measure the supply voltage. Then measure the voltage across the resistance. Also measure the current.
  • 23. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200523 of 34 Circuit 1 results: Supply voltage = Voltage R = Current = Circuit 2 results: Supply voltage = Voltage R = Current = Experiment 3: Cells in a series circuit – results R V V A R V V A Circuit 1 Circuit 2
  • 24. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200524 of 34 Experiment 3: Cells in a series circuit – summary 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. Circuit 1 Circuit 2 R V V A R V V A
  • 25. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200525 of 34 Current and voltage – key ideas Current  In a series circuit, the current is the same in all parts of the circuit.  In a parallel circuit, the current splits up and recombines when the branches of the circuit meet up. (The sum of the current in the branches equals the total current.)  The current depends on the voltage in any circuit. Voltage  In a series circuit, the supply voltage is shared between the components. (The sum of the voltage across each component is the same as the total supply voltage.)  In a parallel circuit, the voltage across each component is the same as the supply voltage.
  • 26. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200526 of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities
  • 27. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200527 of 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.
  • 28. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200528 of 34 Most of the energy from the battery does not produce light – most of it is wasted as heat! chemical energy from battery (e.g. 100J) heat energy of bulb 95 J transferred to 5J transferred to bulb as light energy Energy transfer in electrical circuits
  • 29. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200529 of 34 The efficiency of an energy transfer can be calculated using this formula: total energy input useful energy output %Efficiency = x 100 Calculating energy efficiency This bulb converts 200J of chemical energy form battery into 10J of useful light energy: Efficiency of bulb = 10 200 = 5% x 100( )
  • 30. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200530 of 34 Batteries can power many electrical devices. What sort of energy is electrical energy transferred into in these electrical devices? What’s the energy transfer?
  • 31. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200531 of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities
  • 32. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200532 of 34 Glossary  current – The flow of electricity, measured in amps (A).  efficiency – A measure of how much energy is changed from one form to another.  potential difference – The amount of ‘push’ or electrical energy there is in a circuit, measured in volts (V).  power – The amount of energy that an electrical device uses per second, measured in watts (W).  power station – A place where an energy resource is transformed into electrical energy.  transfer – To move energy from one place to another.  transform – To change energy from one type to another.  voltage – Another name for ‘potential difference’.
  • 33. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200533 of 34 Anagrams
  • 34. © Boardworks Ltd 20041 of 20 © Boardworks Ltd 200534 of 34 Multiple-choice quiz

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