Answer to Question #144656 in Optics for Promise Omiponle

Question

Consider the compound optical system shown in the diagram, where two thin lenses of focal lengths 8.5 cm (left lens) and 5.5 cm (right lens) are separated by a distance 36 cm.

Answer 1

As per the given question,

focal length of the lenses are $(f_1)=8.5cm$

$f_2=5.5cm$

Distance between the lenses are $(d)=36cm$

Hence focal length of the lens will be $\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}-\frac{36}{f_1f_2}$

Now, substituting the values,

$\frac{1}{f}=\frac{1}{8.5}+\frac{1}{5.5}$ $-\frac{36}{8.5\times 5.5}$

$\Rightarrow \frac{1}{f}=\frac{56}{187}-\frac{144}{187}$

$\Rightarrow \frac{1}{f}= \frac{-88}{187}cm$

$\Rightarrow f= \frac{-187}{88}cm$