Power as the rate of energy transfer, P = E/t and P = W/t, with kJ, kW, MW, minutes and hours converted properly.
What you will learn
- Calculate power, energy or time with P = E/t
- Use work done as energy transferred to find a power
- Convert kJ, kW, MW, minutes and hours
Power is how fast
Two kettles can boil the same water.
The one that does it faster has the bigger power: it transfers the energy at a greater rate.
power = energy transferred ÷ time
P = E ÷ t
power = work done ÷ time
P = W ÷ t
Power in watts (W), energy or work in joules (J), time in seconds (s). One watt is one joule every second. Rearranged: energy E = P × t, and time t = E ÷ P. Recall both: they are not on the sheet for AQA, Edexcel or OCR.
Work done is energy transferred by a force. When a crane lifts a load, the work done on it equals the gravitational potential energy it gains. (Working out work from force × distance, W = F s, is in the forces unit.)
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Power is how fast
- The units trap
- Try it: Try it with the real tool
- Try it: Your first power calculation
8 practice questions, marked as you go; about 20 minutes in all.
Key terms
Work done, Standard form, Power
In this unit: Energy stores, transfers and efficiency
Energy stores and how energy moves between them, kinetic and potential energy, specific heat capacity, power, efficiency and the energy resources that make our electricity.