Efficiency and Useful Output

Lab Brief #6

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

The opposite of what you expect is often what happens.

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

efficiency
Useful energy output divided by total energy input.
wasted energy
Energy transferred to stores that are not useful for the purpose, usually thermal.

Make a hypothesis first

Predict: what happens if you double the force?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

small electric motor
string
known masses
metre rule
joulemeter or ammeter and voltmeter
stopwatch

Get ready

⚠️ Safety first

Use a low-voltage supply only — never mains.
Keep the hanging mass over a padded area and feet clear.

Step 1 of 4 · Read

Think about what you just learned: say what "efficiency" and "wasted energy" mean in your own words before you start.

Step 2 of 4 · Do

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.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

A device takes in 500 J and usefully outputs 150 J. Its efficiency is:

How sure are you?😐 maybe

Question 2 of 2

Wasted energy in most machines ends up as:

How sure are you?😐 maybe

Mind = blown

🎢 You feel weightless on a roller coaster because you and the seat are falling at the same speed.

Nice work!

You got 0 of 2 right.

Next: Sankey Diagrams All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: This is why airplanes can fly and why rockets reach space.

🏆 Stretch challenge (try it 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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