Question

A nearsighted person cannot clearly see beyond 200 cm. Find the power of the lens needed to see objects at large distances.

Answer 1

For a near-sighted person, u = ∞.
Now, we have:
v = – 200 cm = – 2 m
The lens formula is given by
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
On putting the respective values, we get:
$\frac{1}{f}=\frac{1}{\left(-2\right)}-\frac{1}{\infty }=-\frac{1}{2}$
∴ Power of the lens = $\frac{1}{f}$ = – 0.5 D