An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short � sighted?

Question

An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short &#xFFFD; sighted?

Philoid · Accepted Answer

If an eye has a near point distance of 0.75 m, then convex lenses should be used.

v = -75 m

u = -25 m

⇒ f = 0.375

Hence Power = 1/f = 1/0.375 = +2.67D

Hence, this eye is long-sighted.