Question:medium

A ray of light is incident normally on one face of an equilateral glass prism of refractive index \( P \). When the prism is completely immersed in a transparent medium, it is observed that the emergent ray just grazes the adjacent face. Find the refractive index of the medium.

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The critical angle condition is used to determine the refractive index of the medium when total internal reflection occurs.
Updated On: Jan 13, 2026
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Solution and Explanation

Snell's Law Application:
- The angle of refraction at the prism's second face equals the critical angle, \( C \), leading to:\[\sin C = \frac{n_{\text{medium}}}{n_{\text{prism}}}\]- For an equilateral prism, the internal angle of incidence is:\[r = \frac{A}{2} = \frac{60^\circ}{2} = 30^\circ\]- The critical angle \( C \) is defined as:\[\sin C = \frac{1}{n}\]Given \( C = 60^\circ \):\[\sin 60^\circ = \frac{n_{\text{medium}}}{n_{\text{prism}}}\]\[\frac{\sqrt{3}}{2} = \frac{n_{\text{medium}}}{n_{\text{prism}}}\]\[n_{\text{medium}} = \frac{\sqrt{3}}{2} n_{\text{prism}}\]Consequently, the refractive index of the medium is \( \frac{\sqrt{3}}{2} n_{\text{prism}} \).
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