An astronomical telescope in normal adjustment receives light from a distant source `S`. The tube length is now decreased slightly

Options

A. no image will be formed
B. a virtual image of S will be formed at finite distance
C. a large, real image of S will be formed behined the eye place,for it
D. a small, real image of S will be formed behind the eye-piece closed to it

Answer

B

Explanation

(b) In an astronomical telescope
`L=f_(0)+f_(e)`
When tube length is decreased, then the image formed by the objective lens will lie between principal focus and opticle centre of eye lens instead of lying at the focus of eye lens. Therefore, a virtual image will be formed at a finite distance from the eye lens.