General Science • PhysicsHard
A double convex thin glass lens having a refractive index of 1.5 is placed in a transparent liquid medium whose absolute refractive index is precisely 1.6. How does the optical behavior of this lens change upon immersion?
A. The lens behaves as a diverging lens because the surrounding medium is optically denser than the lens material✓ Correct Answer
B. The lens retains its converging nature with an increased focal length due to reduced refractive index contrast
C. The lens acts as a plane glass slab with infinite focal length because optical refraction ceases entirely
D. The lens transforms into a total reflector trapping all incident light rays inside its curvature
💡 Solution & Explanation
According to the lens maker formula, when a lens is immersed in a medium whose refractive index exceeds that of the lens material, the sign of the focal length term reverses, transforming a converging convex lens into a diverging concave lens. Retaining convergence requires the lens refractive index to exceed the surrounding medium value. Refraction does not cease unless refractive indices match identically. Total internal reflection occurs only past critical incidence angles rather than normal lens immersion. The focal length magnitude also scales inversely with the relative refractive index difference.
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