Light, as a form of wave obeys certain laws of its own.
They are principally reflection, refraction and lastly total
internal reflection. Later portions of the website will open you up to certain
phenomenas such as diffraction and interference.
Reflection
Whenever light strikes the surface of any material substance, part of the light is turned
back from the surface. This is called reflection. The remainder of the light is
transmitted into the material. If the surface is rough or matted, the reflected light goes
off in all different directions. This is called diffused reflection.
An example is the paper on which this printing appears.
Diffuse reflection of light renders nonluminous objects visible. If the surface is very
smooth, however, the reflected light goes in a definite direction determined by the
direction of the incident light. This phenomenon is known as regular reflection.
The term reflectance is used to denote the fraction of light energy that
is reflected by a material. Metals generally have high values of reflectance, silver being
the best reflector with a reflectance of about 96%. The reflectance of a clean glass
surface is about 6%.
Light is reflected from a plane surface at an angle equal to the angle made by the
incoming (incident) light. The angles of incidence and reflection are customarily measured
as the angles made by the light rays and the normal, a line drawn perpendicular to the
surface at the point of incidence. Thus, the law of reflection states that the angle of
incidence equals the angle of reflection.
If the surface is not plane but curved, it may still be considered to be made up of many
very small, elementary plane surfaces. The path of any light ray striking a curved surface
can still be determined from the law of reflection. This law is the basis for computing
the image-forming characteristics of curved mirrors which will be discussed in detail
later.
