Question

A person needs a lens of power $–4.5D$ for correction of her vision. (a) What kind of defect in vision is she suffering from? (b) What is the focal length of the corrective lens? (c) What is the nature of the corrective lens?

Answer 1

(a) Defect in vision

Myopia is the defect, in this defect the person is unable to see distant objects.

(b) Focal length of the corrective lens

$P=-4.5D$

$$\begin{gathered} \Rightarrow f=\frac{1}{P} \\ \Rightarrow f=\frac{1}{-4.5D} \end{gathered}$$

$\Rightarrow f=-0.22m$

(c) The nature of the corrective lens

The nature of the corrective lens is a concave lens.

Hence, the defect is myopia, $f=-0.22m$ and the concave lens is the nature of the lens.