Speed of EM in a medium

ImaLooser

Visible light propagates at less than c in water.

What about other wavelengths of EM? Do they all travel at the same reduced speed? I think not, but am not sure. If they travel at different speeds then Suzanna can be seen comin' round the mountain in certain wavelengths before others.

ehild

The speed of light in a medium varies a bit with the (vacuum) wavelength. That means changing refractive index (dispersion). http://refractiveindex.info/?gclid=C...FUFO3wodllwA_w


ehild

krd

Not at the same reduced speed. This is how a prism splits light up. Different wavelengths are refracted differently.

If the mountain is a prism, you'll see multiple Suzannas split into all the colours of the rainbow.

ImaLooser

If the mountain is of glass and Suzanna suddenly materializes behind it, then you will see the a violet Suzanna first. If she then dematerializes, you see the red Suzanna last.

voko

The propagation velocity depends on the frequency and the material very significantly. Essentially, the delay in propagation in medium is caused by this process: the EM wave perturbs the atoms, they get "polarized", which creates internal EM field that interfers with the incoming EM, and the combined EM appears to travel slower. Obviously, this process depends on the material and the incoming radiation.