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Re: [Phys-l] refraction question

The problem is that there is no mechanism (at least that I can see -- ahem) by which the eye (or a bit of film, or a CCD) will measure the _wavelength_, rather than the _frequency_. Embed the film (or the CCD) in plastic or glass, and expose it. It records the same color as it does "free", in air (I've done this several times).

Phytoplankton which use chlorophyll spend the vast majority of their time submerged in water, and they still use [predominantly] red light for their charge-separation, just as their air-immersed cousins do. There's no shifting of that reaction to use blue-shifted light, which I would expect if the reactions cared about the wavelength of the light rather than its frequency.



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________________________________
From: Pete Lohstreter <plohstreter@mail.hockaday.org>
To: phys-l@carnot.physics.buffalo.edu
Sent: Sat, April 24, 2010 9:35:41 AM
Subject: Re: [Phys-l] refraction question

Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
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?

But if you were the water - the laser might look green. Since you are
still in the air where the laser looked red before entering the water and
where you saw it when it left the water (back in the air) , it still
looked red. When the light enters the water is does slow down. When it
re-enters the air from the water - it speeds back up and resumes its old
ways - same wavelength - same frequency - same velocity.

I don't see the problem.


Pete Lohstreter "Happy is he who gets to know
The Hockaday School the reasons for things. "
11600 Welch Rd Virgil (70-19 BCE) Roman poet.
Dallas, TX 75229

214-360-6389

plohstreter@mail.hockaday.org

See what our students are doing......
http://home.hockaday.org/physics/index.html


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