Frequency only depends on the source, i.e. frequency changes only when source changes. So, if light ray travels from one medium to another there will be no change in the frequency because the ray still originates from the same source. For any wave,Lf = cwhere, f = frequency, L = wavelength and c = speed of soundWhen light travels from one medium to another there will be a change in its velocity. As a result there will be change in its wavelength since there must be no change in the frequency.