The focal lengths of the lenses of an astronomical telescope are `50cm` and `5cm`. The length of the telescope when the image is formed at the least distance of distinct vision is

Options

A. `45 cm`
B. `55 cm`
C. `(275)/(6)cm`
D. `(325)/(6)cm`

Answer

D

Explanation

Length of the telescope when final image is formed at least distance of distinct vision is
`L=f_(o)+u_(e)=f_(o)+(f_(e)D)/(f_(e)+D)=50+(2xx25)/(5+25)=(325)/(6)cm`