A person cannot see distinctly objects kept beyond. This defect can be corrected by using a lens of power
– 0.5 D
Step (1): Given:
The far point of the person,
This means the person cannot see the objects situated beyond 2 m from the eye.
Step (2): Statement of Myopia:
Short-sightedness is an eye defect that causes the person to see far away objects as blurry or out of focus. The scientific term in use for short-sightedness is myopia.
From the given situation, the person is suffering from short-sightedness (or) myopia. A concave lens is used to correct myopia.
The far point of the given myopic eye, D is at 2 m.
Step (3): Finding the focal length of the lens:
Let the object distance and image distance (v) = distance of far point = -D
Let 'f' be the focal length of the bi-concave lens.
Using the lens formula,
Step (4): Finding the power of the lens:
We know that the required power of the lens,
A concave lens of power of -0.5 D is required to fix the myopic eye.
Hence, the correct answer is (B) – 0.5 D