Study the figure in which the path of a ray of light going from Medium 1 to Medium 2 is shown.
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
(a) Speed of light is more in Medium 1, because the refracted ray bends away from the normal, indicating Medium 2 is optically denser (slower).
(b) The ray bends away from the normal because Medium 2 is optically rarer than Medium 1 — light speeds up when going from a denser to a rarer medium, causing it to bend away from the normal.
(c) Refractive index of Medium 2 with respect to Medium 1:
$$n_{21} = \frac{v_1}{v_2}$$
where $v_1$ = speed of light in Medium 1, $v_2$ = speed of light in Medium 2.
Source: Chapter 9, Section 9.3.2 – The Refractive Index
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Explanation
- The key observation is: ray bends away from normal → it speeds up → Medium 2 is rarer → Medium 1 is denser → speed is higher in Medium 1.
- For (b), always link "bending away from normal" to "denser → rarer" transition and increased speed.
- For (c), the formula $n_{21} = v_1/v_2$ is directly from Eq. 9.5 — note it is speed in medium 1 over speed in medium 2, not the other way.