Question

A thin convex lens made from crown glass (μ = 3/2) has a focal length f. When immersed (one by one) in two different liquids, having refractive indices 4/3 and 5/3 ; it has focal length f₁ and f₂ , respectively. The correct relation, between the three lengths, is

(1) f₁ = f₂ < f

(2) f₁ > f₂ ; f₂ becomes negative

(3) f₂ > f; and f₁ becomes negative

(4) f₁ and f₂ both become negative

Answer 1

(2) f₁ > f₂ ; f₂ becomes negative

From lens maker’s formula

From Eqn. (3), f₂ , has a negative value.