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When sound waves refract, the frequency always remains constant. Thus,
if the velocity decreases, the wavelength also decreases. This same
idea holds for light. When light refracts, the frequency remains
constant. But how does this relate to the COLOR of the light? Does the
color depend on frequency or wavelength?
The reason I ask is that suppose you shine red light (say, 680 nm)
from air into water. Since n = 1.33, both the velocity and wavelength
will decrease by this factor. Thus, (680 nm)/1.33 = 511 nm. This is
the wavelength of green light! We've probably all done this demo with
a red laser, and the beam remains red. So color depends on frequency.
In class I usually say that color depends on wavelength. Lasers are
rated by their wavelength. Instead, should lasers -- like tuning forks
-- be rated by their frequency since this quantity never changes?
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