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© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 34 KS3 Physics 9I Energy and Electricity.

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Presentation on theme: "© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 34 KS3 Physics 9I Energy and Electricity."— Presentation transcript:

1 © Boardworks Ltd of 20 © Boardworks Ltd of 34 KS3 Physics 9I Energy and Electricity

2 © Boardworks Ltd of 20 © Boardworks Ltd of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities

3 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd of 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 of 20 © Boardworks Ltd of 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 Now measure the current using the ammeter at positions 1, 2 and 3.

6 © Boardworks Ltd of 20 © Boardworks Ltd 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 R1R1 A A Circuit 1Circuit 2 R1 R2 A A A

7 © Boardworks Ltd of 20 © Boardworks Ltd of 34 Experiment 1: 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 1Circuit 2 R1R1 A A R1 R2 A A A

8 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd of 34 A1A1 A2A2 A3A3 A4A4 1.Place the ammeter, in turn, at positions 1, 2, 3 and 4. Measuring current in a parallel circuit AmmeterCurrent (A) A1A1 A2A2 A3A3 A4A4 2.Record the ammeter readings in the table.

10 © Boardworks Ltd of 20 © Boardworks Ltd 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. A1A1 A2A2 A3A3 A4A4 A 1 = A 4

11 © Boardworks Ltd of 20 © Boardworks Ltd 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: A1A1 A2A2 A3A3 A4A4 A 1 = (A 2 + A 3 ) = A 4 If the bulbs are not identical, then the current will not split evenly.

12 © Boardworks Ltd of 20 © Boardworks Ltd of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities

13 © Boardworks Ltd of 20 © Boardworks Ltd 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. V3V3 V2V2 V1V1 V Voltage is measured using a device called a voltmeter. In a circuit diagram, a voltmeter is given the symbol.

14 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd of 34 1.Add another resistor (R2) to the circuit as shown. V2V2 Experiment 2: Voltage in a series circuit Circuit 2 R1 R2 V V1V1 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 of 20 © Boardworks Ltd of 34 Circuit 1 results: Voltage (supply) =V Voltage (R1)= V R1 R2 V V1V1 V2V2 R1 V V Circuit 1Circuit 2 Experiment 2: Voltage in a series circuit – results Circuit 2 results: Voltage (supply)=V Voltage (R1)= V Voltage (R2)=V

17 © Boardworks Ltd of 20 © Boardworks Ltd 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. R1R1 R2R2 V V1V1 V2V2 R V V Circuit 1Circuit 2 supply / decreased / voltage / flow / same

18 © Boardworks Ltd of 20 © Boardworks Ltd of 34 Make your own series circuit

19 © Boardworks Ltd of 20 © Boardworks Ltd of 34 V2V2 Connect up this circuit and measure, in turn, the voltage at V 1, V 2 and V 3. Record your results in the table. Measuring voltage in a parallel circuit What do you notice about the results? How can you explain this? VoltmeterVoltage(V) V1V1 V2V2 V3V3 V1V1 V3V3

20 © Boardworks Ltd of 20 © Boardworks Ltd of 34 Make your own parallel circuit

21 © Boardworks Ltd of 20 © Boardworks Ltd of 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 of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd 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 1Circuit 2

24 © Boardworks Ltd of 20 © Boardworks Ltd 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 1Circuit 2 R V V A R V V A

25 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities

27 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd 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 5 J transferred to bulb as light energy Energy transfer in electrical circuits

29 © Boardworks Ltd of 20 © Boardworks Ltd 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 200 J of chemical energy form battery into 10 J of useful light energy: Efficiency of bulb = = 5% x 100 ( )

30 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd of 34 9I Energy and Electricity Contents Measuring current Measuring voltage Energy in circuits Summary activities

32 © Boardworks Ltd of 20 © Boardworks Ltd 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 of 20 © Boardworks Ltd of 34 Anagrams

34 © Boardworks Ltd of 20 © Boardworks Ltd of 34 Multiple-choice quiz


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