How do they determine the speed of light?

Answer 1

-- Measure the distance between two points or objects. The farther apart

they are, the more accurate your final measurement of the speed will be.

-- Measure the time it takes a beam or a pulse of light to travel from

one of them to the other one. Alternatively, put a mirror at one point,

and measure the time it takes the light to go there and come back.

-- Divide the measured distance by the measured time. The quotient

is the speed of the light. If you used the mirror arrangement, then the

speed is double the quotient.

Answer 2

Velocity of a light wave (eg laser) is equal to is frequency multiplied by its wavelength.

You could work it out in a much more simple way though, by getting a laser and shining it at a mirror that's a long way away and timing how long it takes to come back. then divide the distance between the laser and the mirror, by the time it took.. then divide it by two... but you're very likely to make a mistake i don't even reckon superman has reflexes that quick.

Answer 3

Speed = Distance Traveled / Time taken

The first measurements of the speed of light used mirrors several miles apart, a beam of light was shone at a distant mirror and then reflected back onto a mirror rotating at a constant rate, the angle of reflection gave a measure of the time taken for the light to return and hence could be used to measure it's speed through the air.

Michelson used this method to get a pretty accurate measurement in California in the 1920's, it's pretty clunky, but an improvement on the earlier method which used a rotating cog.

Extra Credit

A more modern way to do it is using laser Interferometry - a coherent beam of light of a known frequency is split and sent through two different paths, the light is then re-combined, the wavelength of the light can be determined from changes in the interference pattern when the path lengths are changed.

speed = frequency x wavelength

Answer 4

Well, to put it bluntly: you can't.

To get to the speed of light, approximately 3 billion meters per second, you would need a force to get you there. Assuming that you have mass (which EVERYTHING that is matter does) you would start to speed up to get to the speed of light, or "c". As you get closer and closer to c, you require more and more force to push you. Also, as a side effect, the mass of you and whatever else is accelerating gets larger. Eventually, you would reach a point where you are VERY VERY close to c, but not quite there. In other words, to get to c, you would have to have an infinite amount of force and velocity. Along with this, if you actually manage to get to c, your mass now becomes infinite.

So in a less complicated answer, YOU CAN'T DO IT.

Answer 5

In any environment ... vacuum or material ... the speed of light is determined by the electrical properties of the environment.

Speed = reciprocal of [ square root of { product of (electrostatic permittivity) times (magnetic permeability) } ].

Answer 6

By observing events on Jupiter, which were supposed to be periodic. The differences in time (sometimes the events occurred earlier, sometimes later) were explained by differences in the distance from Jupiter to Earth.

Answer 7

The first serious, but unsuccessful, attempt was made by Galileo who had two people far away from each other, with covered lanterns. One uncovers his lantern, then the other immediately uncovers his on seeing the light from the first. Galileo claimed that he actually tried the experiment, but the two people were less than a mile apart and so he could not detect a time lag.

The next serious attempt was made by the Danish astronomer, Olaus Roemer, in 1676. He measured the speed of light based on observations of the eclipses of the moons of Jupiter by Jupiter. He noticed that there was a difference of about 3.5 minutes when the earth, in its orbit, was moving away from Jupiter and a similar reduction when the earth was moving towards Jupiter. Knowing the speed of the earth's orbit, he worked out the speed of light at around 200,000 km/s.

Since then, many scientists have tried. Foucault, in 1850, used rotating mirrors to arrive at a value of 298,000 km/s. Using rotating mirrors, Cornu found it to be 299,900 km/s in 1875, Michelson in 1880 got 299,910 km/s, Newcomb, in 1883, Newcomb got 299,860 km/s. In 1928, using Kerr cell shutter, Mittelstaedt got 299,778 km/s, in 1932 Pease and Pearson, using a rotating mirror got 299,774 km/s, in 1940, Huttel, using Kerr cell shutter got 299,768 km/s and in 1951, Bergstrand, using Kerr cell shutter got 299,793.1 km/s.

Finally, in 1983, the metre was defined as the distance travelled by light, in vacuum, in 1/299792458 of a second. So the speed of light in vacuum is now exactly 299,792.458 km/s.

Answer 8

The speed of light is determined through various experimental methods, including measuring the time it takes for light to travel a known distance. One common method is using a device called a Michelson interferometer, which splits a beam of light and recombines it to observe interference patterns that can be used to calculate the speed of light.