Reflection
From Halbeeg, the open encyclopedia · Af-Soomaali
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Reflection is a wave behavior: when a wave—such as light, sound, or a water wave—strikes an interface between two different materials, some of the energy bounces back to the material it came from instead of passing through. It is one of three main phenomena that occur at such an interface: reflection, transmission, and absorption.
Reflection is fundamental to mirrors, radar, sonar, and vision in general, because most objects do not emit light but reflect the light that falls on them. The same principle applies to sound waves bouncing back (echoes) and to electromagnetic and radio waves in materials and air.
The law of reflection
When a wave strikes an interface perpendicularly, a line perpendicular to the interface is used, called the normal. The angle of incidence (between the incoming wave and the normal) equals the angle of reflection. Likewise, the incoming wave, the reflected wave, and the normal all lie in the same plane. These two statements are called the laws of reflection.
Types
When a surface is smooth at the scale of the wave's wavelength, specular reflection occurs, producing a clear image, as in a mirror. When a surface is rough, the waves scatter in different directions; this is called diffuse reflection. Because of diffuse reflection, white paper can be seen from any angle but does not produce an image.
Partial and total
The amount reflected depends on the properties of the two materials and the angle of incidence. When a wave travels from a material with lower wave velocity into one with higher wave velocity (for example, light going from water into air) and the angle of incidence exceeds a critical angle, the entire wave bounces back. This is called total internal reflection and is the basis of fiber optics.
Applications
Radar and sonar measure the time it takes for a wave to bounce back to determine the distance to an object. Ultrasound medical imaging uses sound waves reflected from tissue interfaces to generate images. In acoustic engineering, rooms are covered with sound-absorbing materials to reduce echoes.