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JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Geometrical Optics

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Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R)

Assertion (A) : Refractive index of glass is higher than that of air.

Reason (R) : Optical density of a medium is directly proportionate to its mass density which results in a proportionate refractive index.
In the light of the above statements, choose the most appropriate answer from the options given below:
  1. (A)(A) is not correct but (R) is correct
  2. (B)Both (A) and (R) are correct and (R) is the correct explanation of (A)
  3. (C)(A) is correct but (R) is not correct✓ Correct
  4. (D)Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Answer: (C)

Solution

The refractive index of glass is indeed larger than that of air, so the assertion is sound. Optical density, however, measures how strongly a medium slows light and is not fixed by the material's mass density; a denser substance can have a lower refractive index than a lighter one. The reason therefore asserts a false proportionality. The assertion is correct but the reason is not.

JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Single correct option

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