Re: Another student question

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Thu, 13 Nov 1997, Daniel L. MacIsaac wrote:

> 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.

Dan,

I usually ask students to imagine what would happen after a little while
if 10 wavefronts per second passed one fixed point and 11 (or 9)
wavefronts per second passed a fixed point further along. 

I'll let you construct your own understanding from here on.  ;-) 

John