When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts a plane sheet of glass. This implies that the liquid must have refractive index

Options

(a) equal to that of glass
(b) less then one
(c) greater than that of glass
(d) less than that of glass

Correct Answer:

equal to that of glass

Explanation:

1/f = (µₕ / µₘ – 1) (1/R₁ – 1/R₂)
If µₕ = µₘ, then
1/f = (1 – 1) (1/R₁ – 1/R₂)
1/f = 0, f = 1 / 0 = ∞
This implies that the liquid must have refractive index equal to glass.