Wave Interactions

Reflection, refraction, diffraction, and interference of waves

Waves transfer energy without transferring matter. A transverse wave (like a wave on a rope or light) oscillates perpendicular to its travel direction. A longitudinal wave (like sound) oscillates parallel to its travel direction. All waves share four behaviors. Reflection: when a wave hits a barrier, it bounces back — the angle of incidence equals the angle of reflection. This is why you see your reflection in a mirror and hear echoes off walls. Refraction: when a wave passes from one medium to another (air to water, for example), it changes speed and bends. Snell's law (n1 sin theta1 = n2 sin theta2) describes the bending angle. This is why a straw looks bent in a glass of water. Diffraction: waves spread out when passing through a gap or around an obstacle. Smaller gaps (relative to wavelength) cause more spreading. This is why you can hear someone around a corner but not see them — sound waves have long wavelengths that diffract easily, while light wavelengths are tiny. Interference: when two waves meet, they combine. Constructive interference (peaks align) makes a bigger wave; destructive interference (peak meets trough) cancels them out. Noise-cancelling headphones use destructive interference.