How Do Mirrors Interact With Light?
Reflection
A mirror and a bright white piece of paper reflect about the same amount of light: in excess of 90 percent of the light that strike them. The light reflecting from the paper and the mirror also obey the same Law of Reflection: the angle of reflection equals the angle of incidence. A white piece of paper makes a poor substitute for a mirror, however, if one is shaving or applying makeup.
Mirrors
The mirror exhibits "specular" reflection, meaning that it will form an image. Most of the mirrors in homes and businesses are plane mirrors. That is, their surface is flat, and the image they create is the same size as the object that is reflected. Other common mirrors are concave mirrors, like shaving mirrors, which magnify objects, and convex mirrors, like right-side mirrors on cars, in which "objects are closer than they appear."
Paper
The reflection from the paper, on the other hand, is "diffuse"; light striking it is reflected in many different directions because of microscopic irregularities in the surface.
Theories of Light
In the 17th century, Robert Hooke and Isaac Newton had an intense argument over the nature of light. Hooke said it was a wave, and Newton claimed it was a particle. Experiments at the time were inconclusive. Reflection was one of the properties of light which was examined, and it turned out that both the wave theory and the particle theory explained reflection satisfactorily. Certainly, if one considers light to be made up of small particles like billiard balls, the Law of Reflection can easily be demonstrated by how the ball bounces off a cushion.
Modern scientists believe that light is both a particle and a wave. The particle, called a photon, travels with an accompanying wave, and according to this model, sometimes the particle is more apparent, and sometimes the wave. A further enhancement to the theory, called quantum electrodynamics, supposes that light does not actually reflect in the sense that billiard balls do, but that instead, the photons of the incident light electrons in the mirror, and those electrons then give off the photons that are seen as "reflected" light. To continue the billiard ball analogy, it's as if the first ball disappears into the cushion, and a new one pops out. Another facet of the theory is that rather than obeying a "Law of Reflection," the photons actually travel in whatever path--from the object to the mirror to the observer--takes the least amount of time.
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