CBSE Class 10 Answered

Since, the near point of the hypermetropic eye is1m (100cm), the lens used should be such that the rays of light starting from normal near point(25cm) appear to come from the near point of hypermetropic eye.

         Thus,

                   u = -25cm

                   v =-100cm

                 ¹/_f =¹/_v -¹/_u

                   f = ^uv/_u-v

                     = ^{(-25) x (-100)}/ _{(-25) – (-100)}

                     =¹⁰⁰/₃

                     =33.3cm

              P = 100/f

                 = 100/33.3

                 = 3 D

Since the power is positive , lens must be convex.