In a uniform medium (including vacuum) light travels in a straight line.
At a surface where light is moving from one medium or
material into another, other things can happen:
Some light is may be reflected; there may be a frequency
dependence to the reflection, and the object has a color when
viewed with white light.
Some light may be transmitted into the medium. The light
generally will be travelling in a new direction. This is called
refraction, and will be discussed in another unit.
Some light may be absorbed, turning the energy of the light
into other forms.
This unit concentrates on reflection. Reflection includes all cases where
light encounters a surface (can be liquid or gas as well as solid) and does
not all pass into or through the material. We will concentrate
on the case that the surface is smooth and flat, and all the
light is reflected: a mirror.
Then there
is a simple relationship between the direction light is going before and
after it encounters the surface.
Then there
is a simple relationship between the direction light is going before and
after it encounters the surface.