Question

An object has image thrice of its original size when kept at `8 cm` and `16 cm` from a convex lens. Focal length of the lens is
A. `8 cm`
B. `16 cm`
C. Between `8 cm` and `16 cm`
D. Less than `8 cm`

Answer 1

Correct Answer - C
`m=+3`, using `m=(f)/(f+u)`
For virtual image `3=(f)/(f-8)` …(i)
For real image `-3=(f)/(f-16)` ….(ii)
Solving (i) and (ii) we get `f=12 cm`