Lesson 4 of 8 · Waves
The Decibel Scale Is Logarithmic
🌊
🎯 Your mission
Run the experiment. Find out what really happens.
⚡ The twist
Nature loves to surprise the careful watcher.
What you'll learn
Human hearing responds roughly logarithmically to intensity, so the decibel scale adds 10 dB for every tenfold rise in power per square metre. 90 dB is therefore not slightly louder than 80 dB — it carries ten times the intensity, and 100 dB carries a hundred times. That is why safe exposure time falls so steeply as the number climbs, and why amplitude, which sets intensity, must be kept separate from frequency, which sets pitch.
Key words
amplitude
The maximum displacement of a wave from its rest position, which sets the intensity of a sound.
decibel
A logarithmic unit of sound level in which every 10 dB represents a tenfold change in intensity.
Make a hypothesis first
Before you start: write down what you think will happen, and why.
Say your guess out loud — then find out if you were right.
Get ready
🧰 What you need
- sound level meter or phone app
- notebook
⚠️ Safety first
- Do not stand near very loud sources; take readings briefly and from a safe distance.
Step 1 of 4 · Read
Think about what you just learned: say what "amplitude" and "decibel" mean in your own words before you start.
Step 2 of 4 · Do
Use a sound level meter app to record the level in four places — a quiet room, a corridor, a busy road and a hall. Convert each pair of readings into an intensity ratio using the rule that 10 dB is a factor of ten, and rank the places by intensity rather than by decibels.
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 3
Question 2 of 3
Question 3 of 3
Mind = blown
🔬 The more you look, the more nature shows you.
Nice work!
You got 0 of 3 right.
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✨ More to explore
🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.
🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.
👨👩👧 For the dinner table: “What's the most surprising thing you learned today?”
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Ready?
The Decibel Scale Is Logarithmic
Run the experiment. Find out what really happens.
Full screen — no distractions
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Print the whole Waves track
All 8th Grade Waves lessons as a printable PDF, with worksheets and answer keys.