Question

The power of a concave lens is −12.5 D. What is the focal length of the lens?

Answer 1

Power −12.5 D indicates that lens is concave.

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

\[ \Rightarrow - \ 12.5 = \frac{100}{f \text{(in cm)}} \]

\[ \Rightarrow f = -\frac{100}{12.5} \]

\[ \therefore \ f = - \ 8 \ \text{cm} \]

Thus, the focal length of the lens is −8 cm.