Question

A beam of light goes from one material into another. On physical grounds, explain why the wavelength changes but the frequency and period do not

Answer 1

The wave length does change, the frequency does not.

As far as the color goes, you have to realize that color is a perception. Color comes about by light interacting with rods and cones in the retina of your eye. Light does not have an inherent color, it only has color when your brain perceives the signals from your retina. So it really does not make sense to talk about the color changing in a material. Let's say that the wavelength does change in glass versus air. Well, to see the color of the light, that light would have to pass out of the glass or air, pass into your eye, and land on your retina. So the only wavelength that is relevant to color is the wavelength of the light at your retinal cells, not the wavelength of light in a material outside of your eye.

So no, the color does not change when light passes through a different material. In any case, it is the frequency, not the wavelength, that dictates the color perception in your eye. Frequency is really the more fundamental attribute of light and wavelength is only used because it is a bit more convenient.