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Dec 27, 2020 · The speed of light is equal to the distance light travels d divided by the time it takes ∆t : c = d/∆t . Consider that the time for a single wavelength λ to pass a point is the period of the waveform, which is the reciprocal of the frequency v , and you get the speed of light formula: \(c=\nu \lambda\)
- Chris Deziel
We can define a constant of a material that describes the speed of light in it, called the index of refraction n: \[n=\dfrac{c}{v} \label{index} \] where \(v\) is the observed speed of light in the material.
Sep 13, 2017 · This makes the speed of light through the medium dependent on multiple factors which include the frequency (other example factors being refraction index of the material, polarization of the wave, its intensity and direction).
For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
You can calculate this answer using the speed of light formula: distance = speed of light × time. Thus, the distance that the light can travel in 100 seconds is 299,792,458 m/s × 100 seconds = 29,979,245,800 m
The refractive index of air is about 1.0003, and from this equation we can find that the speed of visible light in air is about 90 km/s slower than c. c ( 3 × 10 8 m / s ) is speed of light in vacuum.
The closest thing to that for light in air would be the very weak absorption of light by air, which gradually turns the light energy into heat. Obviously visible light can go a very long way in clean air before much of that happens, since air is nearly transparent.
