A farsighted boy has a near point at 2.3 m and requires contact lenses to correct his vision to the normal near point.What is the correct choice of lens power for the contact lenses?
A)-0.28 diopters
B)+0.28 diopters
C)-3.6 diopters
D)+3.6 diopters
E)+1.8 diopters

Question

Quizplus · Accepted Answer

The lens power required to correct farsightedness is positive. 
The lens power required can be found using the formula: 
Lens power (in diopters) = 1/focal length (in meters)

Given, near point distance = 2.3 m (which is the far point for the farsighted boy)
So, focal length = 1/2.3 m = 0.43 m

To correct the vision to the normal near point, we need to bring the near point to 25 cm (0.25 m) 
So, the new focal length required = 0.25 m

Lens power required = 1/0.25 m - 1/0.43 m = 4 - 2.32 = 1.68 
Therefore, the correct choice of lens power for the contact lenses is +1.68 diopters, which is closest to option D, +3.6 diopters.

A Farsighted Boy Has a near Point at 2