Question

1.Why does dispersion occurs in case of the glass prism but not in case of a rectangular glass slab?
2. We know that during refraction the frequency of the light remains constant . Then in case of a mono-
chromatic light its frequency remains constant but the wavelength change. We know that for a particula
colour there is a particular wavelength range. Then if the wavelength change then how we get the same colour in case of dispersion or refraction