Lesson 1 of 8 · Waves
Using v = fλ with Real Numbers
🌊
🎯 Your mission
Run the experiment. Find out what really happens.
⚡ The twist
Nature loves to surprise the careful watcher.
What you'll learn
Wave speed is set by the medium, so within one medium frequency and wavelength trade off exactly. Sound travels at about 340 m/s in air, so a 170 Hz note has a 2 m wavelength while a 3,400 Hz note has a 0.1 m one. Move that same sound into water, where the speed is about 1,500 m/s, and the frequency is unchanged — the source still vibrates at the same rate — so the wavelength must grow by more than four times.
Key words
wave speed
The distance a wave's energy travels each second, fixed by the medium it is travelling through.
wavelength
The distance between one point on a wave and the identical point on the next wave.
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
- signal generator
- speaker
- tape measure
- hard wall
⚠️ Safety first
- Keep the volume low — sustained loud tones damage hearing.
Step 1 of 4 · Read
Think about what you just learned: say what "wave speed" and "wavelength" mean in your own words before you start.
Step 2 of 4 · Do
Generate steady notes of 200 Hz, 400 Hz and 800 Hz with a signal generator and speaker, and use v = fλ with 340 m/s to predict each wavelength. Then find the positions of quiet spots against a hard wall and measure whether the spacing matches your prediction.
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?
Using v = fλ with Real Numbers
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.