Lesson 3 of 8 · Waves
Refraction Happens Because the Speed Changes
🌊
🎯 Your mission
Set it up. Test it. Be amazed.
⚡ The twist
Nature loves to surprise the careful watcher.
What you'll learn
A wave bends at a boundary because its speed changes there while its frequency does not, so the wavelength must change and the wavefronts pivot. Light slows on entering glass and bends toward the normal; it speeds up on leaving and bends away again, which is why a straight ruler in a beaker appears broken at the surface. Reflection is different: no speed change occurs, and the angle of reflection always equals the angle of incidence.
Key words
refraction
The change of direction of a wave at a boundary, caused by a change in its speed.
normal
The construction line drawn at right angles to a surface at the point where a ray meets it.
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
- ray box
- rectangular glass block
- protractor
- plain paper
- sharp pencil
Get ready
⚠️ Safety first
- Never look directly into the ray box beam.
- Check the glass block for chips before use and carry it with both hands.
Step 1 of 4 · Read
Think about what you just learned: say what "refraction" and "normal" mean in your own words before you start.
Step 2 of 4 · Do
Shine a ray box beam into a rectangular glass block at four different angles of incidence, marking the incident and refracted rays each time. Measure both angles from the normal and tabulate them to show the refracted angle is always the smaller one on entry.
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.
Next Smart Experiment
We'll pick an experiment that matches exactly how you're thinking right now.
✨ 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?”
Share this experiment
Send it to a parent who's looking for a 10-minute kitchen science win.
Ready?
Refraction Happens Because the Speed Changes
Set it up. Test it. Be amazed.
Full screen — no distractions
Done with science? Try something else
Print the whole Waves track
All 8th Grade Waves lessons as a printable PDF, with worksheets and answer keys.