Power (Edexcel A Level Physics)

Revision Note

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Lindsay Gilmour




  • The power of a mechanical process is the rate at which energy is transferred
    • Since work done is equal to the energy transferred, power can also be defined as the rate of doing work or the work done per unit time
  • Power is measured in Watts (W)
    • Since power is energy used per unit time, 1 W = 1 J s–1
  • Power can be calculated using the equation:

Power equation, downloadable AS & A Level Physics revision notes 

Worked example

A car engine exerts the following force for 1.0 km in 200 s.Determine what is the average power developed by the engine.

Exam Tip

Power is also used in electricity, with labels on lightbulbs which indicate their power, such as 60 W or 100 W, which indicate the amount of energy transferred by an electrical current rather than by a force doing work. Just remembering 'energy per unit time' will help, as it doesn't matter what kind of energy is being transferred.

When working with power equations the numbers are often very large, so expect to see kW, MW and even GW in questions.

(In case you forgot... kW means × 103. MW means × 106, and GW means × 109. If you weren't sure, go and revise S.I. Units!)

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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.

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