Question

Why can't a glass slab disperse light?

Answer 1

Dispersion occurs when light is passed through a prism. The dispersion is caused due to the the difference in the angle of deviation for different colours. In the case of a glass slab, the opposite sides are parallel and therefore different colors emerge parallel to each other and are seen simultaneously. Therefore, dispersion doesn’t occur in a glass slab. In a prism, the dispersion occurring at one face in enhanced by the refraction at the other face, but in a glass slab the dispersion occurring at one face is neutralized by refraction at the other face.