Light Refraction Simulator (Snell's Law)
Bend a light ray between air, water, glass and diamond and find the critical angle.
Drag the glowing light source around to change the angle of the ray. Watch it bend, and reflect completely past the critical angle.
About the Light Refraction Simulator (Snell's Law)
Free refraction simulator. Send a laser between air, water, glass and diamond, see Snell's law in action, find the critical angle and watch total internal reflection. Built for physics, the light refraction simulator (snell's law) runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Bend a light ray between air, water, glass and diamond and find the critical angle. Use it to explore physics ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Light Refraction Simulator (Snell's Law)
- Use the controls to change Top material, Bottom material, Incident angle, Laser colour. The simulation reacts instantly.
- Pick an option such as Red, Green, Violet to switch modes or load an example.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Send light from glass into air and find the critical angle.
- Compare water and diamond.
- Use a bigger incident angle to see total internal reflection.
- Change the laser colour.
Key ideas you can learn
- Snell's law: n1 sin θ1 = n2 sin θ2.
- Light bends toward the normal when entering a higher-index material.
- Total internal reflection happens when going to a lower index above the critical angle.
Where this is used in the real world
Lenses in glasses, cameras and microscopes rely on refraction, and optical fibres carry the internet by total internal reflection. Swimmers see the pool bottom shifted because of refraction.
Who is this simulation for?
Physics students in middle school, high school and first-year university, teachers who want a quick demonstration for the projector, and anyone revising for exams. It works well for flipped classrooms because students can explore before the lesson.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is the critical angle?
The incident angle above which light going into a lower-index material cannot refract and is entirely reflected. It equals arcsin(n2 / n1).
What is a refractive index?
The ratio of the speed of light in a vacuum to its speed in the material. Air is about 1.00, water 1.33, glass about 1.5 and diamond 2.42.
Is the Light Refraction Simulator (Snell's Law) free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Light Refraction Simulator (Snell's Law) work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.