F rom Einstein's famous equation E=mc2, we can measure the speed of light by putting the energy value and mass value in the equation. But that's just a theoretical process, practically it is not possible or it will not supply the correct value of speed of light. But in the field of practical physics, we have three methods proposed by HIPPOLYTE FIZEAU , LEON FOUCAULT and ALBERT A. MICHELSON . Now we will see how they measured the speed of light. METHOD 1: FIZEAU METHOD The first measurement of the speed of light from purely terrestrial experiments was reported by the French physicist HIPPOLYTE FIZEAU in 1849. Fizeau's experiment is illustrated below. A light source was focused through a beamsplitter onto an image plane where a spinning toothed wheel was located. The light passing between teeth of that wheel was then projected to a mirror at a distance of about 8 km, where it was collected and then ref...