1) Efficiency is defined as a) the rate of transfer of energy b) cannot be created or destroyed c) percentage of useful energy acheived d) decreases with increased lubrication 2) Could you ever have a device that provides an efficiency of over 100% a) Yes if it is is really well lubricated b) No, it would violate the law of conservation of energy 3) Efficiency is increased by (tick all that are true) a) reducing wasted energy b) increasing lubrication c) reducing heat loss by insulation d) going slower e) Increasing the voltage 4) Efficiencies can be quoted as a decimal or a percentage a) True b) False 5) Calculate the efficiency of a petrol engine that transforms 1000 J of chemical potential energy into 300 J of kinetic energy, and 700 J into wasted heat and sound energy. a) 3 % b) 70 % c) 50% d) 30 % 6) Calculate the effiency of an electric motor that transforms 1000J of chemical potential energy into 975 J of kinetic energy, and 25 J of wasted heat and sound energy. a) 97.5% b) 2.5% c) 25% d) 7.5% 7) Calculate the efficiency of a solar cell that transforms 300 J of light energy into 45 J of electrical energy and 255 J of wasted energy a) 5% b) 15% c) 85% d) 100% 8) Calculate the useful energy transfered if a 98% efficient kettle has a total input power of 2000 Joules. a) 1960 J b) 40 J c) 1800 J d) 2000 J 9) How much energy is transferred as useful energy by a plant that transforms 0.5% of the 200 J of light energy transferred from the Sun. a) 20 J b) 50 J c) 99 J d) 1 J 10) What would the total input energy have to be for a light bulb that is 50% efficient and transfers 40J of light. a) 400 J b) 20 J c) 80 J d) 40 J

Efficiency Calculations

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