A person cannot see the objects distinctly, when placed beyond 2 m. a. Identify the eye defect. b. Give two…
A person cannot see the objects distinctly, when placed beyond 2 m.
a. Identify the eye defect.
b. Give two reasons for this defect.
c. Calculate the power and nature of the lens he should be using to see the distant objects clearly.
d. Draw the ray diagrams for the defective and the corrected eye.
Solution
a. **Myopia (near-sightedness).**
b. Elongation of the eye ball, or excessive curvature of the cornea.
c. The far point is at $2\ \text{m}$, so the corrective lens must have $f = -2\ \text{m}$.
$P = \dfrac{1}{f} = \dfrac{1}{-2} = -0.5\ \text{D}$
He should use a **concave lens of power $-0.5\ \text{D}$**.
d. Ray diagrams: for the defective eye the image of a distant object forms **in front of** the retina; with the concave lens placed before the eye the rays diverge first, so the image is pushed back **onto** the retina.
