A student heats 0.50 kg of water in an electric kettle from 20 ∘C20\ ^\circ\text{C}20 ∘C to 100 ∘C100\ ^\circ\text{C}100 ∘C.
The specific heat capacity of water is 4200 J/kg ∘C4200\ \text{J/kg}\ ^\circ\text{C}4200 J/kg ∘C.
Use the equation: change in thermal energy=mass×specific heat capacity×change in temperature\text{change in thermal energy} = \text{mass} \times \text{specific heat capacity} \times \text{change in temperature}change in thermal energy=mass×specific heat capacity×change in temperature
Calculate the energy transferred to the water.
The kettle has a power of 2.0 kW. It takes 2 minutes to heat the water.
Use the equation: energy transferred=power×time\text{energy transferred} = \text{power} \times \text{time}energy transferred=power×time
Calculate the energy transferred to the kettle from the mains.
Calculate the efficiency of the kettle.
Suggest one way that energy is wasted by the kettle.
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.