Question

why is a spectrum formed by a prism and not by a glass slab?​

Answer 1

A glass prism is able to produce a spectrum when White light passes through it but a glass slab does-not produce any spectrum. explain why is it so? In a parallel glass slab, the rays are refracted at both the parallel sides. ... Hence the white light does not split into consituent spectrum.

Answer 2

it is because the glass slab is of uniform thickness at all the parts but this not the case with prism

i hope this will help you