An astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance [NEET 2…

Question

An astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance [NEET 2016]

Accepted Answer

Correct answer: C. (c) According to question, Focal length of objective lens, (F_o )=+40 cm Focal length of eyepiece lens (F_e )=4 cm Object distance for objective lens (u_o )=-200 cm Applying lens formula for objective lens 1v- 1u= 1f ⇒ 1v- 1-200= 140 ⇒ 1v= 140- 1200= 5-1200= 4200 ⇒v=50 cm Image will be form at first focus of eyepiece lens. So, for normal adjustment distance between objectives and eye piece lense (length of tube) will be v+F_e ⇒50+4 ⇒54 cm

$An astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance [NEET 2016]$

Solution

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