1) The efficiency of a machine is a measure of a) how well it looses energy to the environment b) how nice it looks or sounds c) How well it converts input energy to useful output energy d) how expensive it is 2) The efficiency is usually given as a) a percentage b) a decimal between 0 and 1 c) a number between 1 and 1000 d) a vulgar fraction 3) Units of energy a) watts b) joules c) seconds d) metres 4) Units of power a) watts b) joules c) seconds d) metres 5) Units of time a) watts b) joules c) seconds d) metres 6) Definition of power a) Joules of energy × number of seconds b) kilograms per second c) metres per second per second d) Joules of energy converted per second 7) An LED converts 10 J of energy in 5 seconds. Its power rating is a) 10 W b) 5 W c) 2 W d) 0.5 W 8) A window-wiper motor has a power rating of 400 W. How much energy does it convert in 10 seconds? a) 4 J b) 40 J c) 400 J d) 4000 J 9) A machine converts 1000 joules of input energy into 250 joules of useful output energy. Its efficiency is a) 2.5% b) 25% c) 50% d) 100% 10) An electric motor has a power rating of 500 W. It produces 300 W of useful power. Its efficiency is a) 3% b) 30% c) 60% d) 100%

Efficiency Quiz

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