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# Grade 9 Electricty, resistance, power and energy

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A set of slides created to teach Grade 9 Electricity, resistance, power and energy to learners at Bishops Diocesan College in Cape Town.

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### Grade 9 Electricty, resistance, power and energy

1. 1. Electrical Circuits G9 K Warne V V1 V2 V1 = 1.5 V V2 = 1.5 V Vsupply= 3 v 1.5 + 1.5 = 3 V1 + V2 = Vcircuit = Vcell V R1 R2 VC = 3 V
2. 2. © Boardworks Ltd 2001 SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Electrical cells 1.5V One cell Battery (more than one cell) 3 cells connected in SERIES - (+) side connected to (-) of next cell – GIVES HIGHER VOLTAGE + - Battery – cells connected in parallel – (+) to (+) – SAME VOLTAGE LASTS LONGER 4.5V (1.5+1.5+1.5) 1.5V
3. 3. Measuring Current The Ammeter: • is connected in ………………… in the circuit (the current flows through it) • has a …………………… resistance • Is connected positive to ……………. - negative to …………….. Circuit Symbol: An ………………. measures the ………….. flowing through the circuit. + _ Ammeter ….0.0001 The current is the ……………… of ……………….. passing a point in one ………………………. The symbol for current is “…” the unit is ……. (…). SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
4. 4. Measuring Current. When measuring the current through a ………………., the ammeter is always ………………………….. with that component (in the …………………… as it). A SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
5. 5. Measuring Potential The Voltmeter: • is connected in ……………..to another component in the circuit (the current does NOT flow through it) • has a …………………resistance • Is connected positive to …………………- negative to ……………………………. A Voltmeter measures the POTENTIAL (…………..) of the current flowing through the circuit. + _ Voltmeter V1.50 Resistor V SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
6. 6. Measuring Voltage. When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. We measure the voltage using a device called an voltmeter. In a circuit this is given the symbol The voltage supplied by the battery is shared between all the components in a series circuit This is still a SERIES circuit. V3 V2 V1 SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
7. 7. 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 SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
8. 8. 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. 4. Write down what you have observed:…………………………… ………………………………………………………………………. Experiment: Measuring Voltage R V V Circuit 1 Voltage cell:……….. Voltage circuit:………………….. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
9. 9. Vsupply = Vcircuit The supply voltage is equal to the voltage drop across the whole circuit. NO ELECTRIC POTENTIAL IS LOST IN THE CONDUCTING WIRE. Experiment: Circuit & cell Voltage R V V Circuit 1 Voltage cell: Vsupply Voltage circuit: Vcircuit Voltage circuit: = Voltage of supply Vsupply = Vcircuit SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
10. 10. 1. Set up the circuit as shown above in circuit 1. 2. Measure the voltage of the cell and circiut and current as shown. 3. Now close the switch as in circiut 2. Repeat your measurements. 4. Write down what you have observed:…………………………… ………………………………………………………………………. Open & Closed Circuit R V V Circuit 1 Voltage cell: Voltage circuit R V V Circuit 1 Voltage cell: Voltage circuit A A SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
11. 11. Open & Closed Circuit R V V Circuit 1 Voltage cell: Voltage circuit R V V Circuit 1 Voltage cell: Voltage circuit A A Results Circuit 1: OPEN CIRCUIT Circuit 2: CLOSED CIRCUIT Supply Voltage Voltage R1 Current Supply Voltage Voltage R1 Current SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
12. 12. V1 V2 V3 Voltmeter Voltage (V) V1 V2 V3 Experiment: Voltages in parallel 1. Set up the circuit as shown. 2. Measure all the voltages and record them in the table. 3. Write down what you have observed:…………………………………. ……………………………………………… ……………………………………………… SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
13. 13. Circuit2 R1 V V1 V2 Circuit2 R2 Measure the voltages indicated in the diagram and note what you observe: ………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… V1:……………… V2:……………… Vsupply: ……………… V1 + V2 = …………… Experiment: Voltages in series SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
14. 14. Experiment: Current in a series circuit 1. Set up the circuit as shown above in circuit 1. 2. Measure the current using the ammeter at positions 1 and 2. 3. Note down what you observe: ……………………………………….. ……………………………………….. ……………………………………….. R1 1 2 A Circuit 1 A R1 R2 3 4 5 A A A Circuit 2 1. Add another resistor into the circuit as in circuit 2. 2. Now measure the current using the ammeter at positions 3, 4 and 5. 3. Note down what you observe. …………………………………….. ……………………………………… …………………………………….. …………………………………….. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
15. 15. © Boardworks Ltd 2001 SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe X X X A1 A2
16. 16. WIRE THICKNES S LENGTHS CURRENT (mA) BRIGHTNESS NICHROME 0.2 1 180 BRIGHT 2 140 DIMMER 3 120 NO LIGHT 4 100 NO LIGHT 0.4 1 200 BRIGHT 2 180 DIM 3 180 DIM 4 180 NO LIGHT Length vs Resistance SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
17. 17. 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. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
18. 18. 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 chemical energy lost from the battery. Energy Transfer in Electrical Circuits SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
19. 19. Energy Efficiency We can work out the efficiency of an energy transfer: %Efficiency = x 100 For the bulb efficiency =...................................... .............. energy input ..............energy output SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
20. 20. © Boardworks Ltd 2001 SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Hi - This is a SAMPLE presentation only. My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as other resources, are freely available on my resource sharing website: www.sciencecafe.org.za (paste into your browser if link above does not work) Have a look and enjoy! Keith Warne
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