d is the distance between the wheel and the mirror.
Δt is the time for one round trip.
Then c = 2d / Δt
Fizeau found a value of
c = 3.1 x 108 m/s.
Ray optics (sometimes called geometric optics) involves the study of the propagation of light.
It uses the assumption that light travels in a straight-line path in a uniform medium and changes its direction when it meets the surface of a different medium or if the optical properties of the medium are nonuniform.
The ray approximation is used to represent beams of light.
The rays are straight lines perpendicular to the wave fronts.
With the ray approximation, we assume that a wave moving through a medium travels in a straight line in the direction of its rays.
If a wave meets a barrier, with λ<<d, the wave emerging from the opening continues to move in a straight line.
d is the diameter of the opening.
There may be some small edge effects.
This approximation is good for the study of mirrors, lenses, prisms, etc.
Other effects occur for openings of other sizes.
See fig. 35.4 b and c
A ray of light, the incident ray, travels in a medium.
When it encounters a boundary with a second medium, part of the incident ray is reflected back into the first medium.
This means it is directed backward into the first medium.
For light waves traveling in three-dimensional space, the reflected light can be in directions different from the direction of the incident rays.
Specular reflection is reflection from a smooth surface.
The reflected rays are parallel to each other.
All reflection in this text is assumed to be specular.
Diffuse reflection is reflection from a rough surface.
The reflected rays travel in a variety of directions.
A surface behaves as a smooth surface as long as the surface variations are much smaller than the wavelength of the light.
The normal is a line perpendicular to the surface.