A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens is 4 D , the power of a cut lens will be

Step-by-step solution

Biconvex lens is cut perpendicularly to the principle axis, it will become a plano-convex lens. Focal length of biconvex lens 1 f = n - 1 1 R ₁ - 1 R ₂ 1 f = n - 1 2 R                 ( ∵ R 1 = R , R 2 = - R ) ⟹ f = R 2 n - 1         … . … ( i ) For plano-convex lens 1 f ₁ = n - 1 1 R - 1 ∞ f 1 = R n - 1           … … … … . ( i i ) Comparing Eqs. (i) and (ii),