Question Detail
Question
A hyperopic eye has its near point at 150 cm. What power of lens is required to allow this eye to read an object placed at 25 cm?
Correct Answer
Option C is the correct answer.
Detailed Explanation
For a hyperopic eye, the corrective lens needs to form a virtual image at the eye's near point (150 cm) when the object is at the desired reading distance (25 cm). Using the lens formula
1/f = 1/u + 1/v:u = +25 cm (object in front of lens)v = -150 cm (virtual image formed at the eye's near point, in front of the lens)1/f = 1/25 + 1/(-150)1/f = (6 - 1)/150 = 5/150 = 1/30f = +30 cm = +0.30 mPower = 1/f = 1/0.30 = +3.33 Diopters.
Hint
Remember that the image formed by the corrective lens for hyperopia needs to be a virtual image located at the eye's defective near point. The desired reading distance is the object distance.