Science (086) — AI-generated practice question

When a ray enters the prism at surface AB, it travels from air (rarer) to glass (denser), so it bends towards the normal. At surface AC, it travels from glass (denser) to air (rarer), so it bends away from the normal. Because the two refracting surfaces of the prism are inclined (not parallel) to each other, the bending at each surface is in the same overall direction (towards the base), and the ray emerges at an angle to the incident ray called the angle of deviation.

In a rectangular glass slab, the two surfaces are parallel, so the bending towards the normal at the first surface is exactly equal and opposite to the bending away from the normal at the second surface. Thus the emergent ray is parallel to the incident ray (only laterally displaced), and there is no net deviation.

Source: Chapter 10, Section 10.3; Chapter 9, Section 9.3.1

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• The examiner wants three clear points: (1) why bending occurs at surface 1, (2) why bending occurs (opposite sense) at surface 2, and (3) contrast with slab.
• Key terms to use: rarer/denser medium, towards/away from normal, angle of deviation, parallel surfaces, lateral displacement.
• Do not confuse "opposite directions at two surfaces" (towards normal vs. away from normal) with "opposite net effect" — in a prism, both bendings add up (inclined surfaces), while in a slab they cancel (parallel surfaces).