Energy
Power and Efficiency
AQA GCSE Physics
Power
- Power is the energy transferred each second.
- Power is the rate of energy transfer.
- 1 watt is 1 joule per second: 1 W = 1 J/s.
power = energy transferred ÷ time
P = E / t
power = work done ÷ time
P = W / t
| Quantity | Symbol | Unit |
|---|---|---|
| Power | P | W (watts) |
| Energy transferred | E | J (joules) |
| Work done | W | J (joules) |
| Time | t | s (seconds) |
| Efficiency | none | no unit |
Efficiency
efficiency = useful output energy transfer ÷ total input energy transfer
efficiency = Euseful out / Etotal in
efficiency = useful power output ÷ total power input
efficiency = Puseful out / Ptotal in
- Rearranged: useful power output = efficiency × total power input.
- Rearranged: total input energy transfer = useful output energy transfer ÷ efficiency.
- Efficiency is a decimal or a percentage, and has no unit.
- Efficiency is never greater than 1 (100%).
- To change a decimal efficiency to a percentage, multiply by 100.
Increasing efficiency
- Efficiency increases when a higher proportion of the energy input is usefully transferred.
- So a smaller proportion of the energy is wasted.
- Less work is done against friction, so the efficiency would increase because the proportion of energy usefully transferred would increase.
- A more efficient device needs a lower energy input for the same energy output.
- A water-driven generator: greater mass of water each second.
These notes are part of an Excel with Osman subscription and are not available to print.
That was one page of 44
The rest of AQA GCSE Physics is written the same way
The other 43 pages of AQA GCSE Physics are written exactly like this one, with the mark scheme wording highlighted throughout. A year of the whole course is $6.99.
Subscriptions open as soon as payment processing is approved.