Q. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index
A) less than that of glass
B) equal to that of glass
C) less than one
D) greater than that of glass
Explanation
[Solution from source] By the lens maker's formula 1/f = (μ_g/μ_l − 1)(1/R₁ − 1/R₂). The lens behaves like a plane sheet (no power) only when μ_g/μ_l = 1, i.e. the liquid has the same refractive index as glass, 1.47. A liquid of smaller index would leave it a converging lens. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.