An electric motor is supplied with 500 J of energy. The motor transfers 350 J of energy usefully.
Use the equation:
efficiency=useful output energy transferinput energy transfer\text{efficiency} = \dfrac{\text{useful output energy transfer}}{\text{input energy transfer}}efficiency=input energy transferuseful output energy transfer
What is the efficiency of the motor?
1.431.431.43
0.700.700.70
0.300.300.30
150150150
50 exam-style questions on OCR GCSE Physics 7.2 Power and efficiency, covering 7.2.1 Dissipation of energy, 7.2.2 Energy transfers in domestic devices, 7.2.3 Power ratings of domestic appliances, 7.2.4 Efficiency of energy transfers, 7.2.5 Ways to increase efficiency, 7.2.6 Reducing unwanted energy transfers, and 7.2.7 Thermal conductivity and the cooling of buildings. Each one has a worked solution and a mark scheme showing where the marks go.