Refraction Lab

Explore Snell's law, bending at a boundary, the critical angle, and total internal reflection.

Media

Upper medium n₁1.00

Lower medium n₂1.50

Incident ray

Angle to normal35°

Ray animation1.0×

Display

Calculation

Snell's law
n₁ sin θ₁ = n₂ sin θ₂

Critical angle appears only when n₁ > n₂.

Refraction

Ray bends toward the normal

Light is entering a medium with a higher refractive index, so its speed decreases and the refracted ray bends toward the normal.

Angles are measured from the normal, not from the surface. The reflected ray is always shown because a real boundary generally reflects some light as well as transmitting it.

Refraction & Total Internal Reflection

Interactive ray model

Drag the angle and refractive-index sliders.
Total internal reflection appears automatically.