The walls of a house are thick and are made of a material with a low thermal conductivity.
Which statement explains why this house costs less to keep warm?
Energy is transferred through the walls at a higher rate, so the house warms up faster
The walls store all the energy from the heater, so no energy can leave the house
Energy is transferred through the walls at a lower rate, so less heater power is needed
Energy is transferred through the walls at a lower rate, so the heater power rating rises
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.