A thin convex lens of refractive index 1.5 has 20 cm focal length in air. If the lens is completely immersed in a liquid of refractive index 1.6 , its focal length will be

Step-by-step solution

From lens formula array l 1 f = (a _g-1 ) ( 1 R₁ - 1 R₂ ) = (1.5-1) ( 1 R₁ - 1 R₂ )...(i) array Also, _g= _g _l = 1.5 1.6 aligned & 1 f^ = (, _g-1 ) ( 1 R₁ - 1 R₂ ) & 1 f^ = ( 15 16 -1 ) ( 1 R₁ - 1 R₂ )....(ii) aligned Dividing Eq. (i) by Eq. (ii), we get aligned f f^ & = ( 15 16 -1 ) (1.5-1) =- 1 16 5 f & =-160 ~cm aligned