(a) What is long-sightedness ? State the two causes of long-sightedness (or hypermetropia). With the help of ray diagrams, show :
(i) the ray-defect long-sightedness.
(ii) correction of long-sightedness by using a lens.
(b) What 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 ?
An eye has a far point of 2 m. What type of lens in spectacles would be needed to increase the far point to infinity ? Also calculate the power of lens required. Is this eye long-sighted or short-sighted ?

Answer

(b) Convex lenses ; + 2.67 D ; Long-sighted (c) Concave lenses ; - 0.5 D ; Short-sighted

Explanation

NA