Question

A glass of a convex lens has a power of 10d. When this lens is totally emerged in a liquid it acts as a concave lens of focal length of 50cm. Cal the refractic index of liquid

Answer 1

Hello there !!

let us use Lens maker's formula

1/fa = (µg/µa - 1) * 2/R (bi convex) --(1)

So 1/fl = (µg/µl - 1) * 2/R --(2)

We know µa = 1 and µg = 1.5 (say). Given 1/fa = 10 and 1/fl = 2

1/fl is negative as it becomes concave

Dividing (1) by (2)

and rearranging we get µl = 15/9 = 1.667