Practice portal › Ray Optics and Optical Instruments › Lenses

A convex lens of refractive index 1.5 and focal length 18 cm in air is immersed in water. The change in focal length of the lens will be ______ cm. (Given refractive index of water = 4/3)

Asked in JEE Main 24th Jan 2nd Shift 2023 · Lens maker's formula and power

Answer: 54

Step-by-step solution

(f_w)/(fₐ) = (1.5 - 1)/((1.5)/(4/3) - 1) = (0.5)/(0.125) = 4

f_w = 72 cm

Change = 72 - 18 = 54 cm

→ 54

More Lenses questionsAll Lenses questions →

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.

Practise this with a timer