JEE Main · 2016 · 03 Apr 2016 · Offline · Geometrical Optics

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An observer looks at a distant tree of height 10 m with a telescope of magnifying power of 20. To the observer the tree appears :

(A)10 times nearer.
(B)20 times taller.
(C)20 times nearer.✓ Correct
(D)10 times taller.

Answer: (C)

Solution

The magnifying power of a telescope compares the angle the final image subtends at the eye with the angle the object itself subtends; it does not change the object's real height. Making that angle twenty times larger is exactly what would happen if the tree came twenty times closer, since for small angles the apparent angular size is inversely proportional to distance. So the tree appears twenty times nearer.

JEE Main · 2016 · 03 Apr 2016 · Offline · Single correct option

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