A myopic eye has a far point at 0.60 m. A person wants to read a book held at 25 cm from the eye. Determine the power (in dioptres) of a thin converging lens placed close to the eye that will allow clear reading.

Step-by-step solution

1. Let the object (book) distance be $u=-0.25$ m (negative because it is on the same side as light enters).
2. Let the image distance required for the eye be $v=-0.60$ m (far point).
3. Use the thin‑lens formula $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$.
4. Substitute: $\frac{1}{f}=\frac{1}{-0.60}-\frac{1}{-0.25}=-1.6667+4=2.3333{\text{m}}^{-1}$.
5. Hence the focal length $f=\frac{1}{2.3333}=0.4286$ m.
6. The power of the lens is $P=\frac{1}{f}=2.3333\text{D}$, which rounds to $2.33\text{D}$.
7. So a +2.33 dioptre converging lens is required.

Concept tested: Corrective lens calculation for myopia

Published 13 October 2026 · How this solution was prepared and checked