Efficiency
Efficiency compares useful output to total input.
About this topic
Efficiency = useful energy output ÷ total energy input, often given as a percentage. No real machine is 100% efficient because some energy always dissipates as heat, sound or friction. An LED bulb can convert about 40% of electrical energy to light while an old filament lamp manages 5%.
Improving efficiency means reducing the wasted part, through lubrication, better insulation, streamlined shapes or better design. The wasted energy is not destroyed; it is spread into the surroundings where it is hard to use. Efficiency can also be calculated using power: useful power out divided by power in.
Example: a motor takes 500 J of electrical energy and lifts a load gaining 350 J of GPE. Its efficiency is 350/500 = 70%, and 150 J is wasted as heat and sound. Petrol engines are about 25 to 30% efficient, while electric motors may exceed 90%. Power stations, boilers, solar panels and home heating all have efficiency ratings.
Tip: efficiency can never be above 100%, and if your answer is, check the ratio is output over input. Do not forget to compare the same kind of quantity on top and bottom, such as energy with energy.
Key ideas
- Efficiency = useful ÷ total
- Never above 100%
- Waste usually leaves as heat
Quick check
Use cases: where Efficiency helps
- Homework: review the key idea behind Efficiency before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Efficiency without notes.
- Visual learning: play with the interactive lab to see how Efficiency changes when you adjust its inputs.
- Teaching a friend: explain Efficiency in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Efficiency?
Efficiency compares useful output to total input.
What will I learn in Efficiency?
Efficiency = useful ÷ total. Never above 100%. Waste usually leaves as heat.
Is Efficiency part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Efficiency lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Efficiency?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.