Light and the Electromagnetic Spectrum

Reflection: angle of incidence = angle of reflection (both measured from the normal).

Refraction: waves change direction when entering a different medium because their speed and wavelength change, but their frequency remains constant. Light entering a denser medium slows down and bends towards the normal.

Total internal reflection occurs when light hits a boundary above the critical angle — the light is completely reflected back inside the denser medium. This is used in optical fibres.