question_answer

The length of an astronomical telescope for normal vision (relaxed eye) will be

A)  \[{{f}_{o}}-{{f}_{e}}\]                   

B)  \[{{f}_{o}}/{{f}_{e}}\]

C)  \[{{f}_{o}}\times {{f}_{e}}\]                      

D)  \[{{f}_{o}}+{{f}_{e}}\]

Correct Answer: D

Solution :

                 To see with relaxed eye, final image is formed at infinity. For this, the distance between the                 objective O and eyepiece E is so adjusted such that the image of distant objective formed by the objective falls at the focus of the eyepiece. This will be so, when \[L={{f}_{0}}+{{f}_{e}}\] where L is length of telescope.