Total Internal Reflection and Optical Fibres

Lab Brief #6

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

When light travels from a denser to a less dense medium beyond the critical angle, it reflects entirely back inside. Optical fibres exploit this to carry light for kilometres with almost no loss, which is what carries most internet traffic.

Key words

critical angle
The angle of incidence above which total internal reflection occurs.
optical fibre
A thin glass strand that guides light by total internal reflection.

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

laser pointer
semicircular acrylic block
protractor
bottle with a hole
dark room

Get ready

⚠️ Safety first

Never look into a laser beam or aim it at anyone — even low-power pointers damage the retina.
Keep the laser well away from the water.

Step 1 of 4 · Read

Think about what you just learned: say what "critical angle" and "optical fibre" mean in your own words before you start.

Step 2 of 4 · Do

Shine a laser pointer into a curved stream of water falling from a bottle in a darkened room. Observe the light following the curve, then measure the critical angle of a semicircular acrylic block with a protractor.

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

Total internal reflection occurs when the angle of incidence is:

How sure are you?😐 maybe

Question 2 of 2

Optical fibres carry data using:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: Standing Waves and Resonance All lessons

🎯

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 card

Share this experiment

Send it to a parent who's looking for a 10-minute kitchen science win.

Total Internal Reflection and Optical Fibres

Next Smart Experiment

Share this experiment

Total Internal Reflection and Optical Fibres

Done with science? Try something else

Your Cart (0)