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Re: [Phys-l] refraction question



On 04/24/2010 09:37 AM, curtis osterhoudt wrote:

What about an interferometer placed in the water. That too would show no
change in the fringes because both beams would be effected the same. If
only the experimental beam is passed through water and compared to a
reference beam in the air, then you see a change in wave length of the
experimental beam. Is this not evidence that wavelength does indeed
change as the light changes medium?

That's a good line of reasoning.

However, when I follow that line, I come to the opposite
conclusion. In particular, if you put an UNEQUAL-arm
interferometer in water, the two beams will be unequally
affected, to a very great degree.

This is a nice clean way of observing the index-dependence.

This has practical commercial applications. Geodetic
survey instruments are so accurate these days that they
are affected by the index of the air (which depends on
via the Clausius-Mossotti relation on the density, which
is not known). To correct for this, they use two beams
at different frequencies. They use the known wavelength-
dependence of the index. This gives them two equations
in two unknowns (range and index).