Optics Question 437

Question: A telescope has an objective lens of focal length 200 cm and an eye piece with focal length 2 cm. If this telescope is used to see a 50 meter tall building at a distance of 2 km, what is the height of the image of the building formed by the objective lens

[AIIMS 2005]

Options:

A) 5 cm

B) 10 cm

C) 1 cm

D) 2 cm

Show Answer

Answer:

Correct Answer: A

Solution:

Magnification of objective lens $ m=\frac{I}{O}=\frac{v _{0}}{u _{0}}=\frac{f _{0}}{u _{0}} $

Therefore $ \frac{I}{50}=\frac{200\times {{10}^{-2}}}{2\times 10^{3}} $

Therefore I = 5 x 10^-2 m = 5 cm.



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