Although rare in everyday life who have to rely directly, what is the speed of light, the interest in this issue manifests itself in childhood.Surprisingly, but every day we are faced with the sign of the constant speed of propagation of electromagnetic waves.The speed of light - is a fundamental value by which the entire universe is there in the form as we know it.
Surely, everyone watched as a child of the flash of lightning, followed by her thunder was trying to understand what has caused the delay between the first and second event.Simple mental considerations quickly led to the logical conclusion: the speed of light and sound different.This first encounter with the two important physical quantities.Later, someone gets the necessary knowledge and could easily explain what is happening.What is the reason for the strange behavior of thunder?The answer lies in the fact that the speed of light is about 300 thousand. Km / s, about a million times greater than the speed of propagation of sound vibrations in the air (330 m / s).Therefore, a person first sees a flash of light from the electric arc lightning, and only in time to hear the roar of thunder.For example, if an observer from the epicenter to 1 km, then the light will overcome this distance in 3 microseconds, but the sound will need as much as 3 seconds.Knowing the speed of light and the time delay between flash and thunder is possible to calculate the distance.
attempts to measure it made long ago.Now quite amusing to read about the experiments, however, in those days, before the advent of precision instruments, it was more than serious.When trying to find out what is the speed of light, there was one interesting experience.From one end of the car quickly moving train was a man with a precise chronometer, and on the opposite side of his assistant team opened the flap of the lamp.According to the idea, the chronometer was possible to determine the speed of propagation of photons of light.And thanks to the change of position lamps and chronometer (with the continuing direction of the train) have been able to learn, is constant if the speed of light, or you can increase / decrease (depending on the direction of the beam, in theory, the speed of the train could affect the experimentally measured speed).Of course, the experience was a failure, because the speed of light, and registration is not comparable chronometer.
the first time the most accurate measurement was carried out in 1676 due to observations of Jupiter's moons.Olaf Roemer pointed out that the actual appearance of Io and estimates differed by 22 minutes.When the planets approach each other, the delay decreased.Knowing the distance, it was possible to calculate the speed of light.It was around 215 thousand. Km / s.Then, in 1926, D. Bradley, studying changes in the apparent position of the stars (aberration), drew attention to the pattern.Point star accommodation varied depending on the time of year.Consequently, influence the position of the planets relative to the sun.You can draw an analogy - a drop of rain.Without wind, they fly straight down, but it is run - and the apparent trajectory of change.Knowing the speed of rotation of the planet around the Sun, it was possible to calculate the speed of light.It amounted to 301 thousand. Km / s.
In 1849, A. Fizeau had the following experience: between the light source and a mirror, remote 8 km, was spinning gear.The speed of rotation is increased to as long as the gap in the next stream of reflected light is not turned into a permanent (flicker-free).Calculations gave 315 thousand. Km / s.Three years later, L. Foucault replaced the wheel rotating mirror and received 298 thousand. Km / s.Subsequent experiments
becoming more exact, considering refraction of air and so on. At the moment considered relevant data received via cesium clocks and the laser beam.According to them, the speed of light in a vacuum is equal to 299 thousand. Km / s.
