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© Boardworks Ltd 2003 Teacher’s Notes 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). Notes Page View Normal View Flash Files A flash file has been embedded into the PowerPoint slide wherever this icon is displayed – These files are not editable. © 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 A When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component. A © Boardworks Ltd 2003 Measuring Voltage. We measure the voltage using a device called an voltmeter. In a circuit this is given the symbol V When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. V 1 This is still a SERIES circuit. V2 V3 The voltage supplied by the battery is shared between all the components in a series circuit © Boardworks Ltd 2003 Series circuit animation © Boardworks Ltd 2003 Measuring Voltage - across a resistance or a bulb A Components component here R V Voltage is measured by connecting the voltmeter (or in parallel) with the component. V across Voltage is measured in volts and the symbol for this is V. © Boardworks Ltd 2003 Experiment: Measuring Voltage V Circuit 1 R V 1. 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. © Boardworks Ltd 2003 V Circuit 2 R1 R2 V1 V2 1. Add another resistance (R2) 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. © Boardworks Ltd 2003 Circuit 1 V Circuit2 V R1 R1 R2 V V1 V2 Voltage (supply) = V Voltage (R) = V Voltage (supply) = V Voltage (R1) = V Voltage (R2) = V Record your results: Circuit 1: Circuit 2: © Boardworks Ltd 2003 Circuit 1 V Circuit2 Circuit2 V R1 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 © Boardworks Ltd 2003 Measuring Voltage in Parallel Circuits V1 V2 V3 Connect together the circuit shown above and measure, in turn, the voltage at V1, V2 and V3 © Boardworks Ltd 2003 Write down your results in the table below : Voltmeter Voltage (V) V1 V2 V3 Explain anything you notice about the results © Boardworks Ltd 2003 Parallel circuits © Boardworks Ltd 2003 Experiment: Measuring Current 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. © Boardworks Ltd 2003 Experiment: Measuring Current Circuit 2 1 A A R1 A 3 R2 2 1. Add another resistor into the circuit. 2. Now measure the current using the ammeter at positions 1, 2 and 3. © Boardworks Ltd 2003 Results Circuit 1 Current Position 1 Current Position 2 Circuit 2 Current Position 1 Current Position 2 Current Position 3 © 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 © Boardworks Ltd 2003 Experiment: Cells V Circuit 1 R1 A V 1. 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. © Boardworks Ltd 2003 Experiment: Cells V Circuit 2 R1 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. Measure the current. © Boardworks Ltd 2003 Results Circuit 1: one battery Supply Voltage Voltage R1 Current Circuit 2: two batteries Supply Voltage Voltage R1 Current © 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. © 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. © Boardworks Ltd 2003 Parallel Circuits A B 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. © Boardworks Ltd 2003 Measuring Current in Parallel Circuits 1 A1 A2 A4 2 4 A3 3 Ammeter A1 A2 1. Place the ammeter, in turn, at positions 1, 2, 3 and 4. 2. Record the ammeter reading at the points in the table shown. Current (A) A3 A4 © 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. A1 = A4 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. A1 = A2 + A3 =A4 © 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. © Boardworks Ltd 2003 Energy Transfer in Electrical Circuits 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. lamps © Boardworks Ltd 2003 Energy Transfer in electrical circuits 5J transferred to bulb as light energy Chemical energy lost from battery (e.g. 100J). 95 J Transferred to Heat energy of bulb Notice, most of the energy from the battery does not produce light - most is wasted as heat! © Boardworks Ltd 2003 Energy Efficiency We can work out the efficiency of an energy transfer: %Efficiency = useful energy output x 100 total energy input For this bulb efficiency = (5/100) x 100 = 5%. © Boardworks Ltd 2003 Other energy transfers Batteries can power many things What sort of energy is the electrical energy transferred into in these examples? © Boardworks Ltd 2003