Hi When light passes say from air to glass, there is a change in speed and wavelength but not frequency. So a red laser shone at a glass block will refract but is still the red light with its given frequency. Why is it wavelength and not frequency? I get the feeling that it has something to do with the frequency is a characteristic given to the wave by the source of the oscillation causing the wave motion and that wavelength more a property of the medium it is moving through. Any thoughts or directions for me to explore would be greatly appreciated.