Exampro Electricity High Demand Questions

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The photograph below shows a coffee machine. The coffee machine uses an electric element to 1 heat water. (a)  The coffee machine has a metal case. Why would it be dangerous for the live wire of ... the electric cable to touch the metal case? ___________________________________________________________________ ___________________________________________________________________ (1) (b)  The power output of the coffee machine is 2.53 kW. The mains potential difference is 230 V. Calculate the current in the coffee machine. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Current = ____________________ A (3) Aston Academy Page 2 of 71(c)  The coffee machine heats water from 20 °C to 90 °C. The power output of the coffee machine is 2.53 kW. The specific heat capacity of water is 4200 J/kg °C. Calculate the mass of water that the coffee machine can heat in 14 seconds. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Mass = ____________________ kg (5) (Total 9 marks) (a)  Complete the sentence. Choose answers from the box. charge potential difference power temperature time The current through an ohmic conductor is directly proportional to the _______________________ across the component, provided that the _______________________ remains constant. (2) 2 Aston Academy Page 3 of 71(b)  Figure 1 shows a current − potential difference graph for a filament lamp. Figure 1 Explain how the resistance of a filament lamp changes as the potential difference across it increases. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (3) (c)  Many householders are replacing their filament lamps with LED lamps which are more energy efficient. What does more energy efficient mean? ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (1) Aston Academy Page 4 of 71A Light Dependent Resistor (LDR) is used to turn on an outside lamp when it gets dark. Part of the circuit is shown in Figure 2. Figure 2 (d)  The light intensity decreases. What happens to the potential difference across the LDR and the current in the LDR? Potential difference ___________________________________________________ Current ____________________________________________________________ (2) (e)  What is the resistance of the LDR when the potential difference across it is 4 V? Give a reason for your answer. Explain your answer. Resistance = _______________________ Ω Reason ____________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (2) Aston Academy Page 5 of 71(f)  Calculate the current through the LDR when the resistance of the LDR is 5000 Ω. Give your answer to 2 significant figures. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Current = _______________________ A (4) (Total 14 marks) The picture shows an electric bicycle. The bicycle is usually powered using a combination of the 3 rider pedalling and an electric motor. (a) A 36 volt battery powers the electric motor. The battery is made using individual 1.2 volt cells. (i) Explain how a 36 volt battery can be produced using individual 1.2 volt cells. To gain full marks, you must include a calculation in your answer. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (2) (ii) The battery supplies a direct current (d.c.). What is a direct current (d.c.)? ______________________________________________________________ ______________________________________________________________ (1) Aston Academy Page 6 of 71(iii) When fully charged, the battery can deliver a current of 5 A for 2 hours. The battery is then fully discharged. Calculate the maximum charge that the battery stores. Show clearly how you work out your answer and give the unit. ______________________________________________________________ ______________________________________________________________ Charge stored = ______________________________ (3) (b) When powered only by the electric motor, the bicycle can carry a 90 kg rider at a maximum speed of 6 m/s. Under these conditions, the maximum distance that the bicycle can cover before the battery needs recharging is 32 km. The bicycle has a mass of 30 kg. (i) Calculate the maximum kinetic energy of the bicycle and rider when the rider is not pedalling. Show clearly how you work out your answer. ______________________________________________________________ ______________________________________________________________ Kinetic energy = ______________________________ J (2) (ii) The bicycle can be fitted with panniers (bags) to carry a small amount of luggage. What effect would fitting panniers and carrying luggage have on the distance the bicycle can cover before the battery needs recharging? ______________________________________________________________ Give a reason for your answer. ______________________________________________________________ ______________________________________________________________ (2) (Total 10 marks) Aston Academy Page 7 of 71A homeowner had a new gas boiler installed. (a) The following information is an extract from the information booklet supplied with the boiler. Fuel Natural Gas Water temperature 60 °C Energy supplied to gas boiler 8.0 kJ/s (8.0 kW) Efficiency 0.95 4 (i) Calculate the energy transferred each second by the gas boiler to the water inside the boiler. Show clearly how you work out your answer. ______________________________________________________________ ______________________________________________________________ Energy transferred by the gas boiler each second = ___________ kJ (2) (ii) The energy value of the gas used in a home is measured in kilowatt-hours (kWh). The homeowner has a pre-payment meter and pays £30 into his account. With a pre-payment meter, gas costs 15p per kilowatt-hour. Calculate the total number of hours that the gas boiler would operate for £30. Show clearly how you work out your answer. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Number of hours = _________________________ (2) Aston Academy Page 8 of 71(b) Although the gas boiler is very efficient, some energy is wasted. Explain what happens to the waste energy. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (2) (Total 6 marks) (a) The picture shows a person using a set of electronic ‘Body Fat Scales’. When the person stands on the scales, a small, harmless, electric current passes through the person’s body. The scales then calculate the resistance of the person’s body and convert the resistance into a prediction of body fat content. (i) The scales contain two 3 V cells joined in series. Calculate the resistance of a person’s body, if when he stands on the scales, a current of 0.12 mA passes through his body. 1000 mA = 1 A Show clearly how you work out your answer and give the unit. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Resistance = _______________________________ [Show More]

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