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© Boardworks Ltd 2003. A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97)

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Presentation on theme: "© Boardworks Ltd 2003. A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97)"— Presentation transcript:

1 © Boardworks Ltd 2003

2 A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000). Normal ViewNotes Page View Teacher’s Notes Flash Files A flash file has been embedded into the PowerPoint slide wherever this icon is displayed – These files are not editable.

3 © Boardworks Ltd 2003 Measuring Current. The unit of measure for current is the "amp" which has the symbol A. We measure the current using a device called an ammeter. In a circuit this is given the symbol When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component. AA A

4 © Boardworks Ltd 2003 Measuring Voltage. When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. V3V3 V2V2 V1V1 We measure the voltage using a device called an voltmeter. In a circuit this is given the symbol V The voltage supplied by the battery is shared between all the components in a series circuit This is still a SERIES circuit.

5 © Boardworks Ltd 2003 Series circuit animation

6 © Boardworks Ltd 2003 A V component here R Measuring Voltage - across a resistance or a bulb Voltage is measured by connecting the voltmeter across (or in parallel) with the component. Voltage is measured in volts and the symbol for this is V. V Components

7 © Boardworks Ltd Set up the circuit as shown above. 2.Connect the voltmeter across the power supply and measure the supply voltage. 3.Then connect the voltmeter across the resistance (R) and measure this voltage. Experiment: Measuring Voltage R V V Circuit 1

8 © Boardworks Ltd Add another resistance (R 2 ) to the circuit as shown. 2.Connect the voltmeter across the power supply and measure the supply voltage. 3.Then measure the voltage across each of the resistances. R1R1 R2R2 V V1V1 V2V2 Circuit 2

9 © Boardworks Ltd 2003 Record your results: Circuit 1: Voltage (supply) =V Voltage (R)= V Circuit 2:Voltage (supply)=V Voltage (R 1 ) = V Voltage (R 2 )=V R1R1 R2R2 V V1V1 V2V2 R1R1 V V Circuit 1 Circuit2

10 © Boardworks Ltd 2003 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 Circuit2 R1R1 R2R2 V V1V1 V2V2 R1R1 V V Circuit 1 Circuit2

11 © Boardworks Ltd 2003 V1V1 V2V2 V3V3 Measuring Voltage in Parallel Circuits Connect together the circuit shown above and measure, in turn, the voltage at V 1, V 2 and V 3

12 © Boardworks Ltd 2003 Write down your results in the table below : VoltmeterVoltage (V) V1V1 V2V2 V3V3 Explain anything you notice about the results

13 © Boardworks Ltd 2003 Parallel circuits

14 © Boardworks Ltd 2003 Experiment: Measuring Current R1R1 1 2 A 1.Set up the circuit as shown above. 2.Measure the current using the ammeter at positions 1 and 2. Circuit 1 A

15 © Boardworks Ltd 2003 Experiment: Measuring Current R1 R A A A 1.Add another resistor into the circuit. 2.Now measure the current using the ammeter at positions 1, 2 and 3. Circuit 2

16 © Boardworks Ltd 2003 Results Current Position 1 Current Position 2 Current Position 3 Current Position 1 Current Position 2 Circuit 1 Circuit 2

17 © Boardworks Ltd 2003 Conclusions 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

18 © Boardworks Ltd Set up the circuit as shown above. 2. Connect the voltmeter across the power supply and measure the supply voltage. Then measure the voltage across the resistance. Measure the current. Experiment: Cells R1R1 V V Circuit 1 A

19 © Boardworks Ltd 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. Measure the current. Experiment: Cells R1R1 V V Circuit 2 A

20 © Boardworks Ltd 2003 Results Circuit 1: one battery Circuit 2: two batteries Supply Voltage Voltage R1 Current Supply Voltage Voltage R1 Current

21 © Boardworks Ltd 2003 Conclusions Delete the wrong answer: Increasing the number of batteries / cells increases/decreases the current that flows in the circuit. The current/voltage depends on the current/voltage.

22 © Boardworks Ltd 2003 Summary for Series Circuits. 1.In a series circuit the current is the same at any point in the circuit. 2. The supply voltage is shared between the components in a series circuit. 3. The current depends on the voltage in ANY circuit.

23 © Boardworks Ltd 2003 Parallel Circuits 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 B

24 © Boardworks Ltd 2003 Measuring Current in Parallel Circuits A1A1 A2A2 A3A3 A4A Place the ammeter, in turn, at positions 1, 2, 3 and 4. 2.Record the ammeter reading at the points in the table shown. AmmeterCurrent (A) A1A1 A2A2 A3A3 A4A4

25 © Boardworks Ltd 2003 For a parallel circuit, the current that leaves the cell or battery is the same as the current that returns to the cell or battery. The current does NOT get used up by a circuit, just the energy the electrons are carrying. A 1 = A 4 The current splits up at the first junction and then joins together at the second junction. If the bulbs are identical then the current will split evenly. If the bulbs are NOT identical, then the current will NOT split evenly. The following is always true for this circuit. A 1 = A 2 + A 3 =A 4

26 © Boardworks Ltd 2003 Energy in Circuits This section deals with the energy transfers in electric circuits. The most important thing to understand about energy is that it cannot be created or destroyed. In all devices and machines, energy is transferred from one type to another.

27 © Boardworks Ltd 2003 lamps 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. Energy Transfer in Electrical Circuits

28 © Boardworks Ltd 2003 Energy Transfer in electrical circuits Chemical energy lost from battery (e.g. 100J). Heat energy of bulb Notice, most of the energy from the battery does not produce light - most is wasted as heat! 95 J Transferred to 5J transferred to bulb as light energy

29 © Boardworks Ltd 2003 Energy Efficiency We can work out the efficiency of an energy transfer: %Efficiency = x 100 For this bulb efficiency = (5/100) x 100 = 5%. total energy input useful energy output

30 © Boardworks Ltd 2003 Other energy transfers Batteries can power many things What sort of energy is the electrical energy transferred into in these examples?


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