

InterviewSolution
Saved Bookmarks
1. |
A telescope has an objective of focal length `30 cm` and an eye piece of focal length `3.0 cm`. It is focussed on a scale distant `2.0 m`. For seeing with relaxed aye, calculate the separation between the objective and eye piece. |
Answer» Correct Answer - `37.97 cm` Here, `f_(0) = 30 cm, f_(e) = 3 cm, u_(0) = - 200 cm`. Separation between the lenses `= (v_(0) + |u_(0)|)` From `(1)/(v_(0)) - (1)/(u_(0)) = (1)/(f_(0))` `(1)/(v_(0)) = (1)/(f_(0)) + (1)/(u_(0)) = (1)/(30) - (1)/(200) = (20 - 3)/(600) = (17)/(600)` `v_(0) = (600)/(17)cm = 35.29 cm` From `(1)/(v_(e)) - (1)/(u_(e)) = (1)/(f_(e))` `(1)/(u_(e)) = (1)/(v_(e)) - (1)/(f_(e)) = (1)/(-25) - (1)/(3) = (-28)/(75)` `u_(e) = (-75)/(28) = - 2.68 cm` `:.` Separation between the lenses `= 35.29 + 2.68 = 37.97 cm` |
|