Derivation of the formula for the speed of light. Values and concept

Since school times, we know that the speed of light, according to the laws of Einstein, is an insuperable maximum in the universe. The distance from the Sun to the Earth is 8 minutes, which is about 150 000 000 km. Neptune does not reach until 6 hours, but space vehicles take decades to overcome such distances. But not everyone knows that the value of the speed can vary significantly depending on the environment in which light passes.

Formula for the speed of light

Knowing the speed of light in a vacuum (with ≈ 3 * 10 ⁸ m / s), we can determine it in other media, based on their refractive index n. The very formula of the speed of light resembles the laws of mechanics from physics, or rather, the definition of distance using time and speed of the object.

For example, we take a glass with a refractive index of 1.5. Using the light velocity formula v = c \ n, we find that the velocity in a given medium is approximately 200,000 km / s. If we take a liquid, such as water, then the propagation speed of photons (light particles) in it is 226,000 km / s with a refractive index of 1.33.

Formula for the speed of light in the air

Air is also an environment. Consequently, it has a so-called optical density. If photons do not meet obstacles in their path in a vacuum, then in a medium they spend some time on the excitation of atomic particles. The denser the environment, the more time it takes for this excitement. The refractive index (n) in the air is 1,000,292. And this does not drastically depart from the limit of 299,792,458 m / s.

American scientists managed to slow down the speed of light to almost zero. More than 1/299 792 458 seconds Light speed can not overcome. The thing is that light is the same electromagnetic wave as X-rays, radio waves or heat. The difference is only in the difference between the wavelength and the frequency.

An interesting fact is the lack of mass of a photon, and this indicates the absence of time for a given particle. Simply put, for a photon that was born several million, or even billions of years ago, not a second passed.