A telescope has an objective of focal length 50 cm and an eye-piece of focal length 5 cm. The least distance of distinct vision is 25 cm. The telescope is focussed for distinct vision on a scale 200 cm away. The separation between the objective and the eye-piece is

Question

A telescope has an objective of focal length 50 cm and an eye-piece of focal length 5 cm. The least distance of distinct vision is 25 cm. The telescope is focussed for distinct vision on a scale 200 cm away. The separation between the objective and the eye-piece is (A) 75 cm (B) 60 cm (C) 71 cm (D) 74 cm

Tardigrade Admin · Accepted Answer

(1/vo)+(1/200)=(2/50) ⇒ v0=(200/3)=66.6 cm ∴ L=vo+fe=66.6+5 ≈ 71 cm

Q. A telescope has an objective of focal length $50 c m$ and an eye-piece of focal length $5 c m$ . The least distance of distinct vision is $25 c m$ . The telescope is focussed for distinct vision on a scale $200 c m$ away. The separation between the objective and the eye-piece is

75 cm

60 cm

71 cm

74 cm

$\frac{1}{v _{o}} + \frac{1}{200} = \frac{2}{50}$
$\Rightarrow v_{0} = \frac{200}{3} = 66.6 c m$
$∴ L = v_{o} + f_{e} = 66.6 + 5 \approx 71 c m$

Q. A telescope has an objective of focal length 50cm and an eye-piece of focal length 5cm. The least distance of distinct vision is 25cm. The telescope is focussed for distinct vision on a scale 200cm away. The separation between the objective and the eye-piece is