Question

A plano-convex lens is made of material of refractive index 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is ______.

Options

• 50 cm

• 100 cm

• 200 cm

• 400 cm

Answer 1

A plano-convex lens is made of material of refractive index 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is 100 cm.

Explanation:

R₁ = 60 cm, R₂ = ∝, µ = 1.6

`1/"f" = (µ - 1)(1/"R" - 1/"R"^2)`

`1/"f" = (1.6 - 1) (1/60)`

⇒ f = 100 cm.