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Question:

A giant refracting telescope has an objective lens of focal length 15 m. If an eyepiece of focal length 1.0 cm is used, what is the angular magnification of the telescope?

Solution:

(i)Angular magnification of a refracting telescope is given by: m₀ = f₀/eₘ = 1500/1 = 1500
(ii)Diameter of the image of the moon formed by objective is: d = αf₀
d = Diameter of the moon/Radius of the lunar orbit * f₀
d = (3.48 × 10⁸)/(3.8 × 10⁸) × 15
d = 13.736 m