Q1. [3] medium thorough-understanding
A ray of light travels from glass (refractive index ≈ 1.5) into water (refractive index ≈ 1.33). (i) State whether the ray bends towards or away from the normal at the interface. (ii) Using the relationship between the speed of light and optical density, explain why it bends in that direction.
Generated by claude-sonnet-4-6 · 2026-06-26 01:13 · grounding rag
Model Answer
(i) The ray bends away from the normal at the interface.
(ii) Glass (n = 1.5) is optically denser than water (n = 1.33). A higher refractive index means light travels slower in that medium. So when the ray passes from glass (slower speed) into water (higher speed), it speeds up. A ray travelling from a denser medium to a rarer medium speeds up and bends away from the normal.
Source: Chapter 9, Section 9.3.2 – The Refractive Index
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Explanation
- Key rule to remember: Denser → Rarer = bends away from normal; Rarer → Denser = bends towards normal.
- Compare refractive indices to decide which medium is denser: higher n = optically denser = slower light.
- Glass (1.5) > Water (1.33), so glass is denser. Ray goes denser→rarer, hence bends away from normal.
- Examiners expect you to explicitly link refractive index → optical density → speed → direction of bending. All three steps must appear for full marks.