Question

when a light ray passes from a glass prism it undergoes dispersion but when it passes from rectangular glass slab it does not undergoes dispersion. why???
please explain it briefly.

Answer 1

when we take a rectangular glass slab , both it's sides are parallel so after the refraction on the first side the white light disperses and further recombines on the next surface while in the case of the prism the two sides are at an angle therefore recombination doesn't take place.hope it was helpful

Answer 2

when light passes through a glass prism dispersion occurs due to the white light passing from the prism with different incilination Angle in prism and change in dispersion medium whereas in glass alb there is no inclination of angles , the normal ray and the incident Ray doesn't difracts .