A biconvex lens has radii of curvature of 20 cm and 30 cm . The refractive index of the material of the lens is 1.5 . If the lens is completely immersed in a transparent liquid of refractive index 4 3 , the new focal length of the lens will be :

Step-by-step solution

The relative refractive index of the lens material with respect to the liquid is: _ rel = _g _l = 1.5 4 3 = 9 8 For a biconvex lens, applying the Cartesian sign convention gives R₁ = +20 cm and R₂ = -30 cm . Using the generalized lens maker's formula: 1 f = ( _ rel - 1) ( 1 R₁ - 1 R₂ ) 1 f = ( 9 8 - 1 ) ( 1 20 - 1 -30 ) 1 f = ( 1 8 ) ( 1 20 + 1 30 ) 1 f = 1 8 5 60 = 1 8 1 12 1 f = 1 96 f = 96 cm Answer: 96 cm