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WJEC GCSE Additional Science Teacher’s Notes 2. Being an electrician or an electrical engineer is a really good job. You can work for yourself or for a company. There are a great many opportunities at many different academic levels. Use the following links to find out more about careers involving electricity: www.careerswales.com www.connexions-direct.com Investigate using the links above and also www.futuremorph.org Questions 4. A 12 V solar panel is used to run three household bulbs as shown in Figure 14.10. a Bethany connected a voltmeter across the solar cell. What voltage would she measure during the day 12 V b Explain why her voltmeter would read 0 V at midnight. No sunlight, so no generation of electricity. c During the day, Bethany connected the voltmeter across points A and B in the circuit and turned on switch 1. What would her voltmeter read 12 V d Explain why the lighting circuit has three switches. What does each switch do Switch 1 controls the whole circuit, switching it on and off, Switch 2 controls bulb 1 and Switch 3 controls bulb 2 and bulb 3. e Give an example (from your house) of a circuit like this where two bulbs work off the same switch. For example, wall lights in a lounge. f What is the advantage of connecting bulb 1 with one switch compared to bulbs 2 and 3 which have one switch between them Bulb 1 can be controlled independently – bulbs 2 and 3 are controlled together – they are either both ON or both OFF. g If bulb 2 and bulb 3 are exactly the same (same power rating and brightness), what voltage would Bethany measure if she closed all the switches and connected her voltmeter across points A and C in the circuit 6 V h Why would the voltage rating of bulb 1 be different from the voltage ratings of bulbs 2 and 3 Bulb 1 has 12 V connected across it, whereas bulbs 2 and 3 only have 6 V across them. 5. Measuring voltages in simple circuits in school is quite safe. a Why do electricians have to be much more careful when they are measuring voltages across components in a household wiring circuit The voltages and the currents are usually much higher so the risk of electrocution is higher. b What precautions do you think that they can take to minimise the risks to themselves Good training, turning off the mains when working on any circuit, ensuring all earth connections are connected, making sure the circuit breakers/fuses are working. 51
WJEC GCSE Additional Science Teacher’s Notes c Why is it always a good idea to ask an electrician to do electrical work on your house, if you don’t really know what you are doing Electricians are trained to do mains electrical work safely. 6. Copy and complete Table 14.1 converting ohms to kilohms to megohms. Remember: 1 MΩ = 1 000 000 Ω = 1000 kΩ 1 kΩ = 0.001 MΩ = 1000 Ω 1 Ω = 0.001 kΩ = 0.000 001 MΩ Resistance in ohms, Ω Resistance in kilohms, kΩ Resistance in megohms, MΩ 1 000 000 1 000 1 4 000 4 0.004 2 0.002 0.000 002 3 000 3 0.003 220 000 220 0.220 6 000 000 6 000 6 10 000 10 0.010 PRACTICAL Measuring current and voltage in circuits controlled by a variable resistor (page 159) 1. Graphs of voltage against current for components are called ‘electrical characteristics’. Plot electrical characteristic graphs for the fixed resistor and the bulb. If you can, plot them both on the same graph using the same axes. Student graphs should resemble the one below. The red line is for the fixed resistor, the blue line for the bulb. 52
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