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Question:

A simple telescope, consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focused on a distant object in such a way that parallel rays emerge from the eye lens. If the object makes an angle of 2o at the objective, then the angular width of the image is :

24o

10o

50o

48o

Solution:

Magnification by telescope, M = f₀/fₑ = β/α
β = f₀α/fₑ = 60 × 2 /5 = 24