Question

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

Answer 1

(i) As the power is +0.75 D, therefore the lens is convex.

\[ \text{(ii) Applying, } \mathrm{P} = \frac{100}{f \text{(in cm)}} \]

\[ \Rightarrow 0.75 = \frac{100}{f \text{(in cm)}} \]

\[ \Rightarrow f \text{(in cm)} = \frac{100}{0.75} \]

\[ \therefore \ f = + \ 133.33 \ \text{cm} \]

Thus, the focal length of the lens is 133.33 cm.