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Overview
Reflection is the change in direction of a wave when it encounters a boundary and returns into the medium it came from. Reflection occurs with light, sound, water waves, seismic waves, and many other wave types. In optics, reflection explains mirrors, glare, images, and many visual effects.
Law of Reflection
For smooth surfaces, the angle of incidence equals the angle of reflection. Both angles are measured from the normal, which is an imaginary line perpendicular to the surface.
Incident and Reflected Rays
The incoming path is called the incident ray, and the outgoing path is called the reflected ray. Ray diagrams use these paths to predict reflected light behavior.
Specular Reflection
Specular reflection occurs on smooth surfaces where reflected rays remain organized. Mirrors, calm water, and polished metal can produce clear reflected images.
Diffuse Reflection
Diffuse reflection occurs on rough surfaces where reflected rays scatter in many directions. Most everyday objects are visible because they diffusely reflect light.
Sound Reflection
Sound can reflect from walls, cliffs, buildings, and other surfaces. Echoes, reverberation, and room acoustics depend strongly on sound reflection.
Image Formation
Plane mirrors form virtual images that appear behind the mirror. Curved mirrors can form magnified, reduced, real, or virtual images depending on shape and object position.
Energy and Absorption
Not all wave energy is reflected. Some may be absorbed, transmitted, or scattered depending on the surface and material.
Common Mistakes
A common mistake is measuring reflection angles from the surface instead of from the normal. Another is thinking only shiny surfaces reflect light, even though most visible objects reflect light diffusely.
Why This Matters in Physics
Reflection is foundational for mirrors, optics, acoustics, imaging, sonar, radar, architecture, telescopes, and many wave technologies.