Q1. Calculate the efficiency of the following device as a decimal and also as a percentage.


  • An electrical appliance rated at 60 W with a useful power output of 48 W

  • A machine supplied with 1600 J, but which wastes 275 J to various useless energy stores.


Q2. What is the efficiency of the following lamp? Its transfers 7.5 kJ of energy, 4.5 kJ of this as useful light, 2.9 kJ is transferred to the surrounding thermal energy stores as heat and 100 J is transferred away by sound waves. State efficiency as a decimal and then as a percentage.



Q3. A machine with an efficiency rating of only 47% transfers 697 J of energy to useful energy stores. Calculate the total amount of energy that is supplied to the machine.



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