Question

When a biconvex lens of glass of refractive index 1.6 was dipped in a certain transparent liquid, it was found to behave like a plane sheet of glass. So, the refractive index of the liquid is ______.

Options

• 1.0

• 1.4

• 1.5

• 1.6

Answer 1

When a biconvex lens of glass of refractive index 1.6 was dipped in a certain transparent liquid, it was found to behave like a plane sheet of glass. So, the refractive index of the liquid is 1.6.

Explanation:

A lens behaves like a plane sheet of glass when it does not bend light (its focal length becomes infinite and its power becomes zero).

According to the Lens Maker’s Formula:

`1/f = ((n_"lens")/(n_"medium") - 1)(1/(R_1) - 1/(R_2))`

For the lens to act as a plane sheet, the term `((n_"lens")/(n_"medium") - 1)` must equal 0. This only occurs when the refractive index of the lens `(n_"lens")` is  equal to the refractive index of the liquid `(n_"medium")`.

Since the lens has a refractive index of 1.6, the liquid must also be 1.6.