S10 Measure the Speed of Light

# S10 Measure the Speed of Light - Measure The Speed of Light...

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Measure The Speed of Light With Chocolate and a Microwave http://physics.about.com/mbiopage.htm From Joseph Andersen ,Your Guide to Physics . Nothing travels faster than light - it only takes 8 minutes for it to reach the Earth from the nearest star, the Sun, which is 150 million kilometers away. This means that when you see the sun (remember do not look directly at the sun), you’re really seeing light that left the sun 8 minutes ago – you’re seeing the sun as it was, and where it was, 8 minutes earlier. One of the first to try to measure the speed of light was Galileo. In the early 17th century, the general belief amongst scientists (or natural philosophers as they were often called then) was that the speed of light was infinite; that is, light could travel any distance in no time at all. Just as with many other important discoveries made by Galileo, he disagreed with most of his contemporaries. One of Galileo’s great strengths as a scientist was his ability to conceive experiments to test his theories. To measure the speed of light, he and his assistant each took a shuttered lantern to hilltops one mile apart. Galileo flashed his lantern, and the assistant was supposed to open the shutter to his own lantern as soon as he saw Galileo's light. Galileo would then time how long it took before he saw the light from the other hilltop. Then, he could divide the distance by the time he measured to get a speed. Unfortunately for Galileo, this time he had not conceived an experiment sufficiently clever to measure the extraordinary speed with which light traveled. We now know that light travels at approximately 3x10 8 m/s (that is approximately 1100000000 km/Hr), so it would travel the one mile (1.6 km) between the hills in 0.000005 s (5 microseconds), whereas, even if Galileo could time such a short trip, the assistant could not possibly unshutter his lantern fast enough that Galileo could tell what part of his measurement was the travel time! In fact, due to the extraordinarily high value of c (c is the standard symbol physicists use for the speed of light), there was nowhere on earth any two people could stand so that they could conduct this experiment. In order to make such a direct measurement of the speed of light, one needed a laboratory much larger than the earth! Remarkably, Galileo had effectively created such a Laboratory with another of his discoveries – the moons of Jupiter.

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