Reflection and Refraction

Reflection occurs when a wave bounces off a surface. The key principle is the law of reflection:

Both angles are measured from the normal—an imaginary line perpendicular to the surface at the point where the wave hits. This law applies to all waves: light, sound, and water waves.

Refraction is the bending of waves when they pass from one medium to another. This happens because waves travel at different speeds in different materials.

Light slows down in denser media (like glass or water) and bends toward the normal. When light exits to a less dense medium, it speeds up and bends away from the normal.

Interestingly, sound behaves oppositely—it travels faster in denser media.

The refractive index (n) measures how much a material slows down light:

Snell's Law relates the angles and refractive indices:

Common values: air ≈ 1.0, water ≈ 1.33, glass ≈ 1.5, diamond ≈ 2.4

When light travels from a denser to a less dense medium (e.g., glass to air), there's a special angle called the critical angle. At angles greater than this, the light cannot escape—it all reflects back inside. This is total internal reflection (TIR).

TIR is used in optical fibers to transmit data as light pulses over long distances without signal loss. It's also why diamonds sparkle so brilliantly—their high refractive index creates a small critical angle, trapping light inside.