An engineer wants to reduce the unwanted energy transfers in a factory machine. The machine has moving parts and hot water pipes.
Which pair of changes would both do this?
Lubricating the moving parts and fitting a motor with a higher power
Lubricating the moving parts and thermally insulating the hot pipes
Thermally insulating the hot pipes and using wires with more resistance
Increasing friction between the parts and insulating the hot pipes
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.