A telescope has an objective of focal length 30 cm and an eyepiece of focal length 3.0 cm. It is focused on a scale distant 2.0 m. For seeing with relaxed eye, the separation between the objective and eyepiece would be: |
35.3 cm 38.3 cm 37 cm 30 cm |
38.3 cm |
The correct answer is Option (2) → 38.3 cm Using the lens formula, $\frac{1}{f_o}=\frac{1}{u}+\frac{1}{v_o}$ $\frac{1}{30}=\frac{1}{200}+\frac{1}{v_o}$ $⇒\frac{1}{v_o}=\frac{20-3}{600}=\frac{17}{600}$ $⇒v_o=35.29cm$ Seperation (L) = $f_e+v_o$ $=3.35.29=38.29cm$ |