IN A PRISM DISPERSION OCCURS BUT NOT IN A GLASS SLAB PLEASE EXPLAIN ME CLEARLY WHY IN THE GLASS SLAB THE DISPERSION DOES NOT TAKES PLACE.
Answer: In a glass slab, the opposite sides are parallel. Though splitting up of light takes place inside the glass slab, the emergent rays are parallel to each other and enter simultaneously without any angular separation. But, in the case of a glass prism, the angular separation produced to the component colours due to refraction at the first face is further enhanced at the second face. Thus the angular separation between the emergent colours enables the viewer to see the colours separately and thus the dispersion is observed.