Ramesh cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power
+ 0.5 D
- 0.5 D
+ 0.2 D
- 0.2 D
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC NDA-2 – 2023
– In myopia, distant objects (effectively at infinity) are focused in front of the retina.
– A diverging lens (concave lens) is used to correct myopia, as it diverges incoming light rays slightly before they reach the eye lens, causing them to focus further back on the retina.
– Concave lenses have negative power.
– The corrective lens should form a virtual image of an object at infinity (u = ∞) at the person’s far point (v = -2 m, as the image is virtual and on the same side as the object).
– 1/f = 1/(-2) – 1/∞
– 1/f = -1/2 – 0
– 1/f = -1/2
– The power of the lens P is given by P = 1/f (in meters).
– P = 1/(-2 m) = -0.5 Diopters (D).
– Therefore, a concave lens of power -0.5 D is needed.