A designer wants to increase the efficiency of an electric kettle.
Which change would do this?
Using a longer cable to connect the kettle to the mains socket
Fitting a heating element with a lower power rating to the kettle
Adding a layer of thermal insulation inside the wall of the kettle
Making the wall of the kettle from a metal with a high thermal conductivity
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.