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.

Options

A. `+ 10.0 cm`
B. `- 10.0 cm`
C. `5.0 cm`
D. `- 5 cm`

Answer

A

Explanation

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