When a convex lens is immersed in a liquid of refractive index equal to 80 % of the refractive index of the material of the lens, the focal length of the lens increases by 100 % . The refractive index of the liquid is

Step-by-step solution

When convex lens placed in air, 1 f _ a = ( ₁-1 ) ( 1 R ₁ - 1 R ₂ ) ...(i) When convex lens immersed in medium, 1 f _ m = ( ₁ _ m -1 ) ( 1 R ₁ - 1 R ₂ ) ...(ii) Dividing eq(i) by eq(ii), we get aligned & f_m f_a = ( ₁-1 ) ( ₁ _m -1 ) = ( 5 4 _m-1 ) ( 5 4 -1 ) & 2 f_a f_a =4 ( 5 4 _m-1 )=5 _m-4 & _m=1.2 aligned