Science (086) — AI-generated practice question

In a Glass Slab (no dispersion):
A rectangular glass slab has two refracting surfaces that are parallel to each other. When white light enters the first surface (air → glass), different colours bend by different amounts (violet bends most, red least). However, at the second surface (glass → air), the bending is equal and opposite for each colour, because the surfaces are parallel. All colours emerge parallel to each other and parallel to the incident ray. The colours recombine, and the emergent beam remains white. There is lateral displacement but no dispersion.

In a Prism (dispersion occurs):
A prism has two refracting surfaces inclined at an angle (the angle of the prism). When white light enters the first surface, violet bends most and red bends least. At the second inclined surface, instead of cancelling, the bending adds to the original separation. Since the surfaces are not parallel, the deviation of each colour is different and cumulative. The colours therefore emerge along different paths, forming a spectrum — VIBGYOR — on the screen. This splitting of white light into its component colours is called dispersion.

Key reason: Parallel surfaces (slab) cancel colour separation; inclined surfaces (prism) compound it.

Source: Chapter 9, Section 9.3.1; Chapter 10, Sections 10.3 and 10.4

---

• The examiner wants you to contrast the geometry of the two surfaces — parallel vs. inclined — and link it to whether the colour-wise bending cancels or accumulates.
• Mention VIBGYOR and the fact that violet deviates most, red least (from Section 10.4).
• Use the textbook's own language: "equal and opposite bending at parallel faces," "angle of deviation," "dispersion," "spectrum."
• A common mistake is writing only about the prism; always explain the slab too, since the question specifically asks for both.
• The concluding one-line summary ("parallel → cancel; inclined → compound") is a good examiner-pleasing wrap-up.