An electromagnetic wave travels first in vacuum and then enters a transparent medium of refractive index n. Answer the following questions with proper reasoning.
(i) Explain qualitatively how the wavelength, frequency and wave speed of the wave change when it enters the medium.
(ii) If the frequency of the wave is doubled in the new medium by adjusting the source, describe the corresponding change (increase, decrease or no change) expected in its wavelength and angular frequency, keeping the same medium.
(iii) Give a reason why the colour of visible light perceived by an observer does not change when the light passes from air into water, even though the wavelength changes.