Question

The power of the glasses of a person is $+0.75D$. What is the nature of the lens and what is its focal length?

Answer 1

Step 1: Given data

Power of the lens is, $P=+0.75D$

Step 2: Finding the nature and the focal length ($f$) of the lens

Since the power is positive, i.e. $+0.75D$, it is a Convex lens.

Applying the formula and substituting the known value,

$$\begin{gathered} \mathrm{P}=\frac{100}{f\left(\text{in}\mathrm{cm}\right)} \\ 0.75=\frac{100}{f} \\ f=\frac{100}{0.75} \\ f=133.33cm \end{gathered}$$

Hence, the nature of the lens is Convex and its focal length is $133.33cm$.