Power and efficiency
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 worked examples, 7 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- How fast, not just how much
- What is power?
- The equation, three forms
Read the transcript of the teaching part
Last time
Before we start: last time, in Gravitational potential and kinetic energy, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
How fast, not just how much
Two students carry the same books up the same stairs. One walks and takes a minute. The other runs and takes ten seconds. They do the same work, but the runner does it faster, so the runner has more power.
What is power?
Power is the rate at which energy is transferred, or the rate at which work is done. A bigger power means more energy moved in each second. Power is the work done divided by the time taken. It can also be the energy transferred divided by the time. The unit is the watt. One watt is one joule per second.
The equation, three forms
Power equals energy divided by time. For the energy, multiply power by time. For the time, divide the energy by the power. Time must be in seconds, so change minutes first.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Efficiency · Power · Efficiency · Power.
The whole chapter: Energy, Work and Power, Energy, Work and Power.
Chapter 1.7: Energy, work and power
- Energy stores, conservation and work done 5 min
- Gravitational potential and kinetic energy 6 min
- Power and efficiency 6 min
- Energy resources 7 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.