Light travels from water (refractive index 1.33) into carbon disulphide (refractive index 1.63). In which dir…

Question

Light travels from water (refractive index 1.33) into carbon disulphide (refractive index 1.63). In which direction does the refracted ray bend at the interface — towards the normal or away from it? Justify your answer in terms of the speeds of light in the two media.

Accepted Answer

## Model Answer The refracted ray bends **towards the normal**. **Justification:** Carbon disulphide has a higher refractive index (1.63) than water (1.33). Since refractive index is inversely related to the speed of light in a medium, light travels **slower** in carbon disulphide than in water. When light travels from a rarer medium (water) to an optically denser medium (carbon disulphide), it slows down and bends towards the normal at the interface. *Source: Chapter 9, Section 9.3.2 — The Refractive Index* --- ## Explanation **What examiners look for (3 marks):** - 1 mark: Correct direction — *towards the normal* - 1 mark: Identifying water as rarer (lower n) and carbon disulphide as denser (higher n), and linking higher n to lower speed - 1 mark: Stating the rule — rarer → denser = slows down = bends towards normal **Key rule to remember:** Higher refractive index = lower speed of light = optically denser medium. Light going from rarer to denser always bends towards the normal. Nev…

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