An electric heater has a power rating of 2.4 kW and an efficiency of 90%. It is switched on for 15 minutes.
How much energy is usefully transferred to the thermal store of the room?
1.9×106 J1.9 \times 10^{6}\ \text{J}1.9×106 J
2.2×106 J2.2 \times 10^{6}\ \text{J}2.2×106 J
3.2×104 J3.2 \times 10^{4}\ \text{J}3.2×104 J
2.4×106 J2.4 \times 10^{6}\ \text{J}2.4×106 J
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.