1-when a light ray falls on a piece of glass,it refracts. which of the following concepts doesn't change : speed-frequency-wavelength indeed speed does change because of changing the medium but frequency doesn't . what causes wave length to change?change in speed?(V=freq*wavelength) right?do u have a better explanation? 2-when light falls from a medium of lower optical density to that of higher optical density with an angle of incidence=zero ,of course direction doesn't change but what about speed??speed changes as a result of changing the medium.right?