$A$ prism causes dispersion of white light while a rectangular glass block does not. Explain.

(N/A) In a prism,the refraction of light takes place at two slant surfaces that are not parallel to each other. The dispersion of white light occurs at the first surface of the prism,where its constituent colours are deviated through different angles. At the second surface,these split colours undergo further refraction and separation,resulting in a spectrum.
In a rectangular glass block,the refraction of light takes place at two parallel surfaces. At the first surface,white light splits into its constituent colours upon refraction. However,because the second surface is parallel to the first,these split colours undergo refraction at the second surface in such a way that they emerge as a parallel beam,which recombines to give the impression of white light.