A light bulb has an efficiency of 0.15. It is supplied with 2400 J of energy.
Use the equation:
efficiency=useful output energy transferinput energy transfer\text{efficiency} = \dfrac{\text{useful output energy transfer}}{\text{input energy transfer}}efficiency=input energy transferuseful output energy transfer
How much energy does the light bulb waste?
360 J360\ \text{J}360 J
16 000 J16\,000\ \text{J}16000 J
2385 J2385\ \text{J}2385 J
2040 J2040\ \text{J}2040 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.