The refractive index of a material indicates how much slower the speed of light is in that medium than in a vacuum. The slower speed of light in materials can cause refraction, as demonstrated by this prism (in the case of a prism splitting white light into a spectrum of colors, the refraction is known as dispersion).
The Speed of Light in a vacuum is denoted by the letter c for constant or the Latin celeritas (speed). The speed of light through a transparent medium (that is, not in vacuum) is less than c; the ratio of c to this speed is called the refractive index of the medium. n metric units, c is exactly 299,792,458 meters per second or 1,079,252,848.8 kilometers per hour. Converted to approximate imperial units, it is 186,282.397 miles per second, or 670,616,629.384 miles per hour. For scale, the distance from the Earth to the Moon is about 239,000 miles. This seems pretty fast and indeed theory says that nothing can travel faster than the speed of light.
In our every day lives light seems to travel from one place to another instantaneously. When we flip on the light in a room there is no delay between when we first see the bulb start glowing and when light illuminates the far corners of the chamber. Our nervous systems are much too slow to notice the rays of light that appear from the bulb and move like a wave washing over the room.
When we deal with the immense distances of space, though, even light seems slow. When astronauts were on the Moon it took over a second for the radio waves (which travel at the speed of light) carrying their voices to reach us. Light coming from the sun takes eight and one half minutes to hit Earth. (This means that if the sun were suddenly to go dark, it would take over eight minute for us to notice) Light from the nearest stars, other than the sun, takes four and a half years to get here. From the farthest stars in distant galaxies it can take billions of years for the light to arrive..
The distance light can travel in a year is called a "light year." The light year is one of the basic measures of distance for astronomy.
When designing probes for trips to other planets in our solar system it is important for the planners to keep the communications time lag, caused by the speed of light, in mind. For example, a probe designed to land on Mars must be smart enough to handle problems in the flight on it's own without instructions from Earth. If a course change is needed during landing the probe would have to do it automatically. The delay caused by the probe requesting instructions from Earth and getting commands back might be nearly an hour, plenty of time for the probe to crash.
The delay caused by the speed of light can sometimes be noticed here on Earth during telephone calls. Long distance calls that have been routed over one or more space satellites may cause a half second or so delay between the speaker and the listener.
The speed of light has several properties which may seem counter-intuitive to us, but are true:
-Nothing travels faster than the speed of light. Although there has been speculation that it may be possible under certain precise conditions.
-No matter how fast you are moving the speed of light seems to be the same speed as if you were not moving at all.
-As an object or person is accelerated toward the speed of light time slows down for it/him.
This last property leads to the "twins" effect: Twin brothers live on Earth. One brother takes a trip to a distant star traveling at a high percentage of the speed of light. When the twin returns he will be younger than his brother because for him time slowed down during the trip.
This effect, called "time dilation," helps explain why the speed of light is the same no matter how fast you are going. As a traveler accelerates time slows down for him. This, in turn, affects his measurements.
The Speed Of Electricity
We are told, by physicists, that electricity travels the same exact speed, through a wire, that light travels through a vacuum (the famous speed c or Latin celeritas). There are two problems with that, aren't there?
- Electricity is the flow of electrons. Electrons have mass. Relativity says that things with mass cannot travel at the speed c. Only things with no mass (zero rest mass) can (and must) travel at c.
- Even light cannot travel at c, when it is traveling through other substances. Light slows down, to travel through glass, water, or air. So, how can electrons travel at c, through copper?
Well, it turns out that physicists are right; electricity does travel at c. Also, electrons do not travel anywhere near c, within a wire. Electricity travels at c, while electrons do not.
Look at the picture, above left. When an electron enters one end of the wire, an electron leaves the other end of the wire. This effect takes place at the speed of light (c). But, they were not the same electron. A different electron exited the wire. And that clears up my two objections, above.
Rest mass is the mass that an object has, when it is at rest. Objects increase in mass when they speed up, as dictated by Special Relativity, and as observed in experiments. Light has a zero rest mass, even though it can never be at rest. This is another consequence of the same equations that predict that masses increase with speed.
The first paragraph, of this article, is meant to sound skeptical about the speed of electricity being c. I did that for artistic reasons; I like the article better that way. But it is also a trap. Perhaps I can trap some physicist, who will read only that paragraph, and then give me the same arguments that I stated, why electricity can travel at c.
Celeritas is a Latin word, translated as "swiftness" or "speed". It is often given as the origin of the symbol
"c", the universal notation for the speed of light in a vacuum, as popularized in Albert Einstein's famous equation
The Lux (symbol: lx) is the International System of Units unit of luminance. Lux is a derived unit based on lumen, and lumen is a derived unit based on candela. It is used in photometry as a measure of the intensity of light, with wavelengths weighted according to the luminosity function, a standardized model of human brightness perception. In English, "lux" is used in both singular and plural.
This is where we got the Name of our website luxceleritas.net for
Light Speed Networks.
The Internet would not exist if not for the Electrons moving through all the Wires or the Photon moving through Fiber Optics and the Networks that connect everything together at Light Speed!