A convex lens of focal length `25 cm` is placed co-axially in contact with a concave lens of focal length `20 cm`. Determine the power of the combination. Will the system be converging or diverging in nature ?

Explanation

`"Focal length of convex lens "=+25cm`
`"Focal length of concave lens "=-20cm`
`(1)/(f)=(1)/(f_(1))+(1)/(f_(2))rArr (1)/(f)=(1)/(25)-(1)/(20)=-(1)/(100)`
`rArr" "f=-100cm`
`"Power "=(100)/(f(cm))=-1D`
It will be diverging combination.