1. Which of these shows the correct units for both energy and power? A kilowatt joule B joule kilojoule C kilojoule watt D watt kilowatt

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1 Multiple choice 1. Which of these shows the correct units for both energy and power? Energy Power A kilowatt joule B joule kilojoule C kilojoule watt D watt kilowatt 2. Which of these could cause an electrical fire in the home? 1. Old, frayed wiring 2. Over-loaded sockets 3. Miniature circuit breakers 4. Damaged plugs A. 1, 2 and 3 B. 1, 2 and 4 C. 2, 3 and 4 D. All of these 3. A residual current circuit breaker (RCCB) works because it... A. detects any difference in current between the live and neutral wires. B. stores any additional current that is passing through the circuit. C. detects any difference in current between live and earth wires. D. detects any current passing though the earth wire. 4. Which of the following electrical appliances would use the most electricity (electrical energy in kilowatt-hours)? A. 60 W light bulb used for 1 hour B. 1 kw hairdryer used for 5 minutes C. 40 W tablet computer used for 2 hours D. 600 W microwave used for 10 minutes Page 1 of 6

2 Inside of a three-pin plug and three fuses./ Credit: SHEILA TERRY/SCIENCE PHOTO LIBRARY / Universal Images Group / Copyright Science Photo Library / For Education Use Only. This and millions of other educational images are available through Britannica Image Quest. For a free trial, please visit uk/trial 5. Which of these statements about a household plug is not correct? A. The fuse should always be a 13 A fuse. B. The live wire is connected closest to the fuse. C. The blue wire is the neutral wire. D. The earth wire is at zero voltage. 6. An electrician rewired a room to include two new ceiling lights. These he connected in parallel so that if one blew the other would still work. Both lights could be switched on from one switch. The electrician then wanted to include a protective fuse for these lights. Live wire Mains D Neutral wire C A B In which position A, B, C, or D in the above circuit diagram should the protective fuse be placed? Page 2 of 6

3 Question 7 and Question 8 These two questions refer to identical heating elements in an electric oven. They are represented by R and S in the diagrams. By using a suitable switch they can be connected in various ways so that they can produce the low, medium and high for the oven. R 240 V Low 240 V Medium 240 V High R S S S The oven operates at 240 V and each heating element has an electrical resistance of 30 Ὠ when cold but this rises to 40 Ὠ under normal operating conditions. 7. If the wire to the heating element R is broken, the oven could still be heated with the switch set to... A. medium only B. medium or high C. low, medium or high D. high only 8. What is the current used by the oven when it is set on low setting? A. 3 A B. 6 A C. 8 A D. 12 A Page 3 of 6

4 Structured Questions 9. The diagram shows a 240 V electric hair dryer. Switch S 1 is the mains switch and switches S 2 and S 3 are the switches for the heating coils. S 2 S 3 Electric fan Two heating coils Plastic case S 1 Mains plug A. (i) Explain why the heating coils are arranged in parallel? [1 marks] Can the heating coils be switched on without the electric fan being on? Explain your answer. [2 marks] B. The electric fan takes a current of 0.5 A, and each heating coil takes a current of 1.5 A. (i) What is the resistance of each heating coil? [2 marks] Which fuse rating (3 A, 5 A or 13 A) should be used in the mains plug? Explain your choice. [2 marks] Page 4 of 6

5 10. Complete the paragraph about electrical safety in the home by choosing from the following list of words. Each word can only be used once. [5 marks] electrician energy electrocution circuit breakers overheating clean wet socket switch fuses appliances Electricity in the home is potentially dangerous and... of wires can cause electrical fires. Electric shock or... can occur if you touch live wires. Always play it safe and use suitable... in plugs and... in main s circuits. Never plug in too many... into one Always... off electric lights, if not in use, to save..., but never switch off with... hands. Never... an electrical appliance that is switched on. Finally always get a qualified... to do electrical repairs if a fault is discovered. [Total = 20 marks] Page 5 of 6

6 Answers 1. C Energy is measured in kilojoules (or joules) and power is measured in watts (or kilowatts). 2. B Miniature circuit breakers (MCB s) are a safety device on mains circuits to prevent electrical fires occurring in the home. 3. A The residual current circuit breaker detects any difference in current between the live and neutral wires in the supply cable. 4. D To calculate the number of units of electrical energy used by the appliance, multiple the power in kilowatts of the appliance by the amount of time switched on in hours. The 60 W lightbulb for 1 hour = 0.06 kw x 1 h = 0.06 kwh The 1 kw hair-dryer for 5 minutes = 1 kw x (5 60 h) = kwh The 40 W tablet for 2 hours = 0.04 kw x 2 h = 0.08 kwh The 600 W microwave for 10 minutes = 0.6 kw x (10 60 h) = 0.1 kwh 5. A The amperage of the fuse used inside the household plug depends on the power of the appliance that is attached to the plug. Appliances with less than 1 kw power should use a 3 A or 5 A fuse, and not a 13 A fuse. 6. D For safety, the protective fuse and also the switch, are placed on the live wire - so if there is a fault the electricity flow is stopped as quickly as possible. 7. B If the wire in heating element R is broken, only the low arrangement would not have a complete circuit. Therefore medium or high (key B) would still work. However the high setting would only produce medium heat. 8. A Under low oven conditions the two heating elements are in series so their combined resistance is 40 Ω + 40 Ω = 80 Ω. Using the relationship: current (A) = voltage (V) resistance (Ω) = = 3 A 9. A (i) Heating coils are in parallel so that either one or both of the coils can be switched on using switches S 2 and S 3. No because switch S 1 must be closed for electricity to reach either of the heater switches S 2 or S B (i) Using the relationship for the heating coil: resistance (Ω) = voltage (V) current (A) = = 160 Ω The fuse rating depends on the total current passing through the circuit. Total current = current in electric fan + total current for both electric heaters = 0.5 A + (2 x 1.5 A) = 3.5 A A suitable fuse would therefore be a 5 A fuse. This will allow the hairdryer to function with both heaters on and the electric fan working but will break the circuit if the current exceeds 5 A. 10. Electricity in the home is potentially dangerous and overheating of wires can cause electrical fires. Electric shock or electrocution can occur if you touch live wires. Always play it safe and use suitable fuses in plugs and circuit breakers in main s circuits. Never plug in too many appliances into one socket. Always switch off electric lights, if not in use, to save electricity, but never switch off with wet hands. Never clean an electrical appliance that is switched on. Finally, always get a qualified electrician to do electrical repairs if a fault is discovered Page 6 of 6