Convex lens of focal length f made of glass of refractive index 1.5 is immersed in water of refractive index 4 / 3 . Focal length is

Step-by-step solution

Given, _ g =1.5, _ w = 4 3 From lens Maker's formula, aligned & 1 f = ( _ g -1 ) ( 1 R₁ - 1 R₂ ) & 1 R₁ - 1 R₂ = 1 f ( _ g -1 ) ...(i) aligned When lens is immersed in water, then aligned 1 f^ &= ( _ g _ w -1 ) ( 1 R₁ - 1 R₂ ) &= ( _ g _ w -1 ) 1 f ( _ g -1 ) [using Eq. (i)] f f^ &= ( 15 4 / 3 -1 ) 1 (15-1) &= ( 9 8 -1 ) 2= 1 4 f^ &=4 f or f^ >f aligned The focal length of lens is greater than f in water.