(i) A giant refracting telescope has an objective lens of focal length 15 m. If an eye piece of focal length 1.0 cm is used, what is the angular magnification of the telescope?
(ii) If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens ? The diameter of the moon is 3.48 × 10⁶ m and the radius of lunar orbit is 3.8 × 10⁸ m.

Solution

(i)
Angular magnification is given by,

Error converting from MathML to accessible text.

where,
f_o is the focal length of the objective lens, and

f_e is the focal length of the eye-piece.
ii)
Given, diameter of the moon = 3.48 × 10⁶ m

Radius of the lunar orbit = 3.8 × 10⁸ m
Diameter of the image of moon formed by the objective lens is given by, d = $straight alpha space straight f subscript straight o$
$straight d space equals space fraction numerator Diameter space of space the space moon over denominator Radius space of space the space lunar space orbit end fraction space cross times space straight f subscript straight o$
$Error converting from MathML to accessible text.$

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