A filament lamp is supplied with 60 J of energy each second.
It transfers 6 J of energy each second usefully as light. The rest of the energy is transferred by heating to the thermal store of the surroundings.
Calculate the efficiency of the filament lamp.
An LED lamp also transfers 6 J of energy each second usefully as light.
The efficiency of the LED lamp is 0.75.
Calculate the total energy supplied to the LED lamp each second.
Explain why the energy transferred by heating from the filament lamp is described as wasted.
100 exam-style questions on Edexcel GCSE Physics 3.2 Dissipation and efficiency, covering 3.2.1 Dissipation of energy, 3.2.2 Reducing unwanted energy transfers, 3.2.3 Efficiency, and 3.2.4 Increasing efficiency. Each one has a worked solution and a mark scheme showing where the marks go.