JEE Main 2025 Apr 7 Shift 2, Physics Q14: Refraction at Plane and Spherical surfaces
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 :
- A
(A) is not correct but (R) is correct
- B
Both (A) and (R) are correct and (R) is the correct explanation of (A)
- C
(A) is correct but (R) is not correct
- D
Both (A) and (R) are correct but (R) is not the correct explanation of (A)
Glass indeed has a higher refractive index (about 1.5) than air (about 1.0003), so the assertion is correct.
However, optical density (refractive index) and mass density are distinct physical properties: optical density is governed by how light interacts electromagnetically with the medium, whereas mass density is simply mass per unit volume. There is no general proportionality between them, and counter-examples exist (for instance, kerosene has a lower mass density than water but a higher refractive index). Hence the reason is incorrect.
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