Snell's Law Refraction

About this simulation

Snell's Law Refraction traces a ray across a boundary with a dashed normal line. Students change the incident angle from 0 to 85 degrees, choose water, glass or diamond, and decide whether the light starts in air or in the material. Readouts show the refracted angle, the critical angle and the reflected and transmitted shares calculated from the Fresnel equations. It supports lessons on refractive index, bending of light and total internal reflection in prisms and optical fibers.

What students can explore

Start in Air and compare the refracted angle for Water, Glass and Diamond.
Switch Light starts in to Material and raise the angle until the ray stops leaving.
Read the Critical angle for each material and compare them.
Watch the Reflected and Transmitted values as the angle approaches 85 degrees.
Set the angle to 0 and check that the ray does not bend.

Learning objectives

1Apply n1 sin theta1 equals n2 sin theta2 to find a refracted angle.
2Explain why light bends when it changes speed.
3Define the critical angle and total internal reflection.
4Compare refractive indices of common materials.

Questions teachers ask

Is the Snell's Law simulation free?

Yes. It is free, needs no sign-up and runs in any modern browser, including whiteboards, tablets and Chromebooks.

What is total internal reflection?

When light travels from a denser to a less dense material and hits the boundary beyond the critical angle, none escapes. All of it reflects, which is how optical fibers keep light inside.

How do I use it?

Choose a material and whether light starts in air or in the material, then change the incident angle. Angles are measured from the dashed normal. Read refracted angle and critical angle.

Why does diamond bend light more than water?

Diamond has a higher refractive index, about 2.42 compared with 1.33 for water, so light slows more inside it and bends more at the surface.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

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