To measure the speed of light in an experiment available to do at school.

The apparatus is set up like the figure below shows. When we did the experiment and measured, x was measured to approximately 3.0 mm - 3.5 mm. So we know that the velocity of light is the distance it travels divided by the time it takes ( c = d / t ), and the distance is 30 meters since the light should travel to the second mirror and back. The how do we know how long time it takes? Well, if we use a tuning fork we can set the mirror to do 512 rotations per second. And since we know the distance between the rotating mirror and the laser, and the angular velocity of the rotating mirror, we can calculate how long time it takes.

So

q = x / 10 = 3

E-4T = 1 / 512 " 0.001953

t = q / 2p * T = ( 0.3E-4 m / 2p ) * ( 1 / 512 ) = 9.32E-8

Then,

c = d / t = 30 / 9.32E-8 " 321719678 m/s " 322 000 km/s

When we are measuring these small distances with a ruler, and using such high velocities as the speed of light, it is very hard to be precise and the result may vary quite much. According to the book the velocity of light is 299,792,458 m/s, so it wasn't that bad measured, but on the other hand, the difference is approximately 22,000km/s which is a very high velocity.