A reflecting type telescope has a concave reflector of radius of curvature `120 cm`. Calculate the focal length of eye piece to secure a magnification of `15`.

Answer

`4 cm`

Explanation

Here, `R = 120 cm, f_(e) = ? m = 15`
`f_(0) = R//2 = 120//2 = 60 cm`
From `m = (f_(0))/(f_(e))`
`f_(e) = (f_(0))/(m) = (60)/(15) = 4 cm`