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Re: Another student question



I've been asked yet another question I am at a loss to explain. I think it's
of the "Why isn't torque measured in Joules?" calibre.

In optics, when a ray of light changes media its frequency is said to be
unaffected, but its wavelength is changed to reflect the change in velocity
in the new medium and /nu = /lambda * f.

Why is frequency unchanged and wavelength changed? Why not both, or a
frequency shift? My handwaving response is that frequency is more directly
related to energy (a more fundamental measurement) and energy conservation
is the reason. I also did a little handwaving through the Xray scattering
treatment of an optical medium as a crystalline array of scattering objects
retarding total velocity but not changing frequency.

BUT I don't have any real confidence in this explanation, and I told my
students I would pose this question to my peers. So here it is.

What is it that generates the wave in the transparent medium?

It is generated by radiating oscillating charges.

What makes the charges oscillate?

The incident wave.

With what frequency do the charges oscillate?

With the frequency of the incident wave.

With what frequency do the charges radiate?

With the same frequency.

Leigh