Fizeau experiment for the speed of light (stationary medium)
The Fizeau experiment for the determination of the speed of light in a stationary medium is an experiment designed and performed by the French physicist Armand Hippolyte Louis Fizeau (1819–1896). The experiment's purpose was to determine the speed of light directly in the laboratory, as opposed to the determination of the speed of light using an interpretation of astronomical data.
Fizeau used the experimental setup that is schematically depicted in the figures on the right. It consisted of a pair of cogwheels that where in such a position that the cogs of one of the wheels were opposite to the intercog openings of the other wheel. If the wheels are not rotating, light from the source cannot be detected, because it will always hit either a cog of the first wheel or a cog of the second wheel.
However, if the wheels are set in a fast rotation, so fast that they rotate the equivalent of one cog in the time it takes for a pulse of light to travel from one of the wheels to the other, a pulse of light that goes through an intercog opening of the first wheel, will also go through an intercog opening of the second wheel.
Fizeau measured the amount of light transmitted by the system at various rotational speeds. The maximum transmission of light happens when the rotational speed of the wheels is such that in the time it takes for a pulse of light to travel from one wheel to the other, the wheels have rotated the equivalent of one cog. Measurements of the rotational speed, the distance between the cogs on the wheels and the distance between the wheels allowed Fizeau to infer the speed of light.
He also placed different (stationary) mediums between the two cogs. In this way, he was for example able to experimentally establish the fact that light moves slower in water than in air.
