A converging lens of focal length `5.0cm` is placed in contact
with a diverging lens of focal length `10.0cm.` Find the combined focal length of
the system.

Explanation

Here `f_(1)` =+5.0cm and `f_(2)` =-10.0cm
Therefore, the combined focal length F is given by
`1/F= 1/(f_(1)) + 1/(f_(2))=1/5 - 1/10 = +1/10`
`:.` F = +10.0cm ie. the combination behaves as a converging lens of focal length 10.0cm