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JEE Mains · Physics · STD 12 - Ray optics and optical instruments
  • JEE Mains 2025
  • Hard
  • MCQ

A hemispherical vessel is completely filled with a liquid of refractive index \(\mu\). A small coin is kept at the lowest point \((\mathrm{O})\) of the vessel as shown in figure. The minimum value of the refractive index of the liquid so that a person can see the coin from point E (at the level of the vessel) is _______.

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Answer & Solution

Correct Answer

(D) \(\sqrt{2}\)

Step-by-step Solution

Detailed explanation


For the rays from coin to reach the point \(E\), the refracted rays must grazing the surface, i.e. they must be incident at critical angle \(\theta_c\) inside the liquid.
\(\mu=\frac{1}{\sin \theta_c}\)
\(\mu\) is minimum when \(\theta_c\) is maximum.
Maximum value of \(\theta_c=45^{\circ}\)
\(\Rightarrow \mu\) has a minimum value of \(\sqrt{2}\).
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