An illuminated sign contains a power supply, a control unit and a lamp. The sign operates for 40 s with a constant input power of 200 W.
All the energy transferred usefully by the power supply is supplied to the control unit. The control unit has an efficiency of 0.90, and all its useful output is supplied to the lamp. The lamp has an efficiency of 0.20 for producing light.
During the 40 s, the lamp transfers 1152 J usefully as light.
Calculate the energy dissipated by the power supply during the 40 s.
128 exam-style questions on Edexcel GCSE Physics 8.3 Power and efficiency, covering 8.3.1 Power and 8.3.2 Efficiency. Each one has a worked solution and a mark scheme showing where the marks go.