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

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?

TestHub · Accepted Answer

From the formula for convex lens, ​ v 1 ​ − u 1 ​ = f 1 ​ ∴ v = u − f f × u ​ = [ 200 × 1 0 3 − 200 ] 200 × 200 × 1 0 3 ​ = 999 200 × 1 0 3 ​ . ​ Also, magnification, m I ​ = ​ u v ​ ​ = ​ O I ​ ​ = 999 × 200 × 1 0 3 200 × 1 0 3 ​ = 50 × 100 I ​ = 999 5000 ​ ≃ 5 cm . ​

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