Lesson 6 of 10 · Energy
Experiment⭐ 30 XP⚡ Spark LabEfficiency and Useful Output
Efficiency and Useful Output.
🎯 Your mission
Run the experiment. Find out what really happens.
⚡ The twist
The opposite of what you expect is often what happens.
Mind = Blown
🎢 You feel weightless on a roller coaster because you and the seat are falling at the same speed.
Make a hypothesis first
Predict: what happens if you double the force?
What You'll Learn
Efficiency is useful output energy divided by total input, usually given as a percentage. No real device reaches 100%: some energy always ends up dissipated as heat. An LED lamp reaching about 40% beats an old filament bulb at roughly 5%.
Key Words
Tap a word to see its definition.
Materials Needed
- small electric motor
- string
- known masses
- metre rule
- joulemeter or ammeter and voltmeter
- stopwatch
Safety First
- Use a low-voltage supply only — never mains.
- Keep the hanging mass over a padded area and feet clear.
Steps
Read the explanation above and note the two key terms before you start.
Use a joulemeter or the rating and running time to find the energy supplied to a small motor lifting a known mass through a measured height. Compare energy in with mgh out and state the efficiency.
Record what actually happened, including anything that did not match what you expected.
Write a conclusion that answers the question this lesson opened with, and state your uncertainty.
Check Your Understanding
Question 1
1 of 2A device takes in 500 J and usefully outputs 150 J. Its efficiency is:
Where you see this in real life
This is why airplanes can fly and why rockets reach space.
Stretch Challenge
Try this in real life this week.
This week, find one thing in your house that turns one kind of energy into another.
For the dinner table
“Show me something at home that uses this kind of energy.”
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Efficiency and Useful Output
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