Question

Two lenses of focal lengths $0.2m$ and $0.3m$ are kept in contact. Find focal length and power of the combination.

Answer 1

Lens combination formula.

$\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}=\frac{1}{0.2}+\frac{1}{0.3}$

$f=0.12m$

Hence, focal length is $0.12m$

Power is $P=\frac{1}{0.12}=\frac{25}{3}Dioptre$