The Core Principles of Wave-Boundary Interactions
Waves, whether they are light, sound, or water waves, exhibit predictable behaviors when they encounter a boundary or transition into a different medium. These fundamental interactions are categorized into three main phenomena: reflection, refraction, and diffraction. Each describes a distinct way a wave's direction, speed, or propagation characteristics change, governing how we perceive the world around us and how various technologies work.
Reflection: When Waves Bounce Back
Reflection occurs when a wave strikes a surface or boundary and bounces back into the medium from which it originated. A key principle of reflection is that the angle at which the wave hits the surface (angle of incidence) is equal to the angle at which it bounces off (angle of reflection). Common examples include seeing your image in a mirror (light reflection) or hearing an echo in a large room (sound reflection). During reflection, the wave's speed and frequency remain constant, but its direction of travel changes.
Refraction: Waves Bending Through New Media
Refraction is the bending of a wave as it passes from one medium into another, such as from air to water or from glass to air. This bending happens because the wave changes its speed as it moves through the new medium. For example, a pencil submerged in water appears broken or bent due to the refraction of light. The amount of bending depends on the properties of the two media and the angle at which the wave enters the new medium, described by Snell's Law.
Diffraction: Waves Spreading Around Obstacles
Diffraction is the phenomenon where waves spread out as they pass through an opening or around the edges of an obstacle. This spreading is most noticeable when the wavelength of the wave is similar in size to the aperture or obstacle. A common illustration is hearing sounds from around a corner even when you can't see the source; this is due to sound waves diffracting. Light also diffracts, which is evident in the patterns created when light passes through a narrow slit or around tiny particles, contributing to effects like the shimmering of a CD or the colors in a soap bubble.