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Doc Brown's Physics AQA GCSE Additional Science-PHYSICS Revision Notes

Physics Unit P2.4 Using mains electricity safely and the power of electrical appliances

PHYSICS UNIT 2 Physics 2 for GCSE Additional Science or GCSE Physics Study Notes

REVISION NOTES GUIDE SUMMARY: What do you need to know for the examinations? What do you need to able to do in the exams? In AQA GCSE Science A examinations HT means for higher tier students only. Sorry, but I don't have much time to answer questions, but if you see any apparent errors or wish to comment, please email me. All my notes, learning objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4 syllabus specification.

 PHYSICS UNIT 2 Physics P2 for GCSE Additional Science or GCSE Physics AQA GCSE Science PHYSICS 2 Unit P2.4 Using mains electricity safely and the power of electrical appliances Appreciate that mains electricity is useful but can be very dangerous and it is important to know how to use it safely. Know that electrical appliances transfer energy. Know and understand that the power of an electrical appliance is the rate at which it transforms energy. Know and understand that most appliances have their power and the potential difference of the supply they need printed on them. Appreciate that from this information we can calculate their current and the fuse they need. You should be able to use your skills, knowledge and understanding to: understand the principles of safe practice and recognise dangerous practice in the use of mains electricity, compare the uses of fuses and circuit breakers, evaluate and explain the need to use different cables for different appliances, consider the factors involved when making a choice of electrical appliances eg you should consider the efficiency and power of the appliance. AQA GCSE Science PHYSICS Unit P2.4.1 Household electricity a) Know and understand that cells and batteries supply current that always passes in the same direction. Know that this is called direct current (d.c.). b) Know and understand that an alternating current (a.c.) is one that is constantly changing direction. You should be able to compare and calculate potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces. HT only: You should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces. c) Know and understand that mains electricity is an a.c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V. d) Know that most electrical appliances are connected to the mains using cable and a three-pin plug. e) Know the structure of electrical cable. You should be familiar with both two-core and three-core cable. f) The structure and wiring of a three-pin plug. Knowledge and understanding of the materials used in three-pin plugs is required, as is the colour coding of the covering of the three wires. g) Know and understand that if an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire. h) Know and understand that when the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit. i) Know that some circuits are protected by Residual Current Circuit Breakers (RCCBs). You should realise that RCCBs operate by detecting a difference in the current between the live and neutral wires. Knowledge of how the devices do this is not required. You should know that this device operates much faster than a fuse. j) Know and understand why, appliances with metal cases are usually earthed. Know that some appliances are double insulated, and therefore have no earth wire connection. k) Know that the earth wire and fuse together protect the wiring of the circuit. You should have an understanding of the link between cable thickness and fuse value. AQA GCSE Science PHYSICS Unit P2.4.2 Current, charge and power a) Know that when an electrical charge flows through a resistor, the resistor gets hot. You should understand that a lot of energy is wasted in filament bulbs by heating. Know that less energy is wasted in power saving lamps such as Compact Fluorescent Lamps (CFLs). You should understand that there is a choice when buying new appliances in how efficiently they transfer energy. b) The rate at which energy is transferred by an appliance is called the power. Be able to use the equation: power = energy transferred / time P = E / t P is power in watts, W E is energy in joules, J t is time in seconds, s c) Know that power, potential difference and current are related by the equation: Be able to use the equation: power = current x voltage (p.d. volts) P = I x V P is power in watts, W I is current in amperes (amps), A V is potential difference in volts, V You should be able to calculate the current through an appliance from its power and the potential difference of the supply, and from this determine the size of fuse needed. d) HT only: Energy transferred, potential difference and charge are related by the equation: HT only: Be able to use the equation: energy transferred = voltage (p.d.) x charge E = V x Q E is energy in joules, J V is potential difference in volts, V Q is charge in coulombs, C Practical work in unit 2.4 to help develop your skills and understanding may have included the following: measuring oscilloscope traces demonstrating the action of fuse wires, using fluctuations in light intensity measurements from filament bulbs to determine the frequency of a.c., measuring the power of 12 V appliances by measuring energy transferred (using a joulemeter or ammeter and voltmeter) in a set time.
• AQA GCSE Additional Science PHYSICS

• When revising, these pages provide you with a summary of what you need to know and be able to do.

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• AQA GCSE Additional Science GCSE Physics Unit P2 Index:

GCSE Science-Physics courses AQA GCSE Science A PHYSICS  *  EDEXCEL GCSE Science PHYSICS

OCR GCSE 21st Century Science A PHYSICS  *  OCR GCSE Gateway Science A PHYSICS

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