Physics
Reflection
Quick fact
The law of reflection was known to ancient Greeks; Euclid described it around 300 BC. It applies to all wave phenomena, including light, sound, and water waves.
Why this is interesting
Have you ever wondered why you can see your face clearly in a mirror but not on a plain wall? The answer lies in a simple yet powerful phenomenon: reflection.
Read the full explanation
Understanding Reflection
When light hits a surface, the behavior depends on the surface's smoothness at a microscopic scale. If the surface is very smooth, like a mirror, all light rays bounce off at the same angle, preserving the image. This is specular reflection. If the surface is rough, like paper or a wall, light scatters in many directions—this is diffuse reflection and prevents a clear image. The key rule is simply this: the angle at which the incoming light strikes the surface (measured from an imaginary perpendicular line called the normal) equals the angle at which it leaves. This is the law of reflection. It works for every ray of light, whether from the sun or a lamp.
A deeper explanation
Reflection is a consequence of the wave nature of light interacting with matter. When an electromagnetic wave strikes a boundary, the electric field of the wave causes electrons in the material to oscillate. These oscillating electrons re-emit waves in all directions, but only those that constructively interfere in the direction obeying the law of reflection produce a strong reflected wave. This principle explains not only mirrors but also how radar, sonar, and seismic imaging work. Reflection is crucial in everyday life: our ability to see most objects relies on diffuse reflection, while mirrors, periscopes, and telescopes depend on specular reflection. Understanding reflection is the first step in designing lenses, lasers, and optical communication systems.