Kettle A has a power rating of 3.0 kW. Kettle B has a power rating of 2.0 kW. Both kettles waste the same fraction of the energy supplied.
Each kettle heats 1.0 kg of water from 20 ∘C20\,^\circ\text{C}20∘C to 100 ∘C100\,^\circ\text{C}100∘C.
Which statement is correct?
Both transfer the same energy to the water, but kettle A takes less time
Kettle A transfers more energy to the water, so the water gets hotter
Kettle B transfers more energy to the water, because it takes longer
Both take the same time, but kettle A transfers more energy to the water
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.