Armand FizeauThe speed of light measured by using a rotating wheel He was a French physicist who was known as being the first physicist to develop the experimental method of determining the speed of light on the Earth. Before his discovery, the speed of light was measured based on astronomical phenomena. In 1839, Fizeau was working with the new daguerreotype photography and Foucault approached him about his efforts based on the same object. Both decided to combine their efforts and together, they developed daguerreotype photography for astronomical observations. They did this by taking the first detailed photographs of the sun’s surface in 1845. They both also discovered that the heat rays came from the sun, undergoing interference and their radiant heat acts as a wave motion. Another contribution Fizeau helped to determine the speed of light on the Earth was by using a cogwheel. He placed the cogwheel and the mirror several miles apart, which was set up to sllow a pulse light beam passing between them. As the cogwheel rotates, he was able to see the light beam passing through the cogs of the wheels to the distant mirror and reflected back. He was able to obscure the reflection by spinning the wheel very fast, which meant that the reflected light beam struck the cog. His proposal indicated that the time it took for the wheel to move the width of one cog must be equal to the time it takes for the light beam to travel to the mirror and back to strike the cog. By understanding the rotational speed of the cogwheel, the width of one cog, and the distance to the mirror, Fizeau was able to make the simple calculation of the speed of light. Fizeau studied another important phenomenon of light. He conducted more experiments and showed that the velocity of light is constant, despite of the motion of the medium it is passing through. Before this discovery, there was a statement that light traveled at different rates through different mediums. With Fizeau’s discovery, it was shown that if the medium was in motion, the velocity of the speed of light increased. He measured the speed of light through flowing liquids by conducting his studies. He found out that this experiment resulted having the velocity of light did not increase by the movement of the liquids. |
