A person's near point is 25 cm, and her eye lens is 2.7 cm away from the retina. What must be the focal length of this lens for an object at the near point of the eye to focus on the retina?

Question

Quizplus · Accepted Answer

The lens formula is 1/f = 1/v - 1/u, where f is the focal length, v is the image distance (distance from the lens to the retina), and u is the object distance (distance from the lens to the object). For an object at the near point to be focused on the retina, u = -25 cm (negative because the object is in front of the lens), and v = 2.7 cm (positive because the image is formed on the retina behind the lens). Plugging these values into the lens formula gives 1/f = 1/2.7 - 1/(-25) = 1/2.7 + 1/25. Solving for f gives f ≈ 2.4 cm.

A Person's near Point Is 25 Cm, and Her Eye