Question

(a) A giant refracting telescope at an observatory 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?

(b) 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 × 10 6 m, and the radius of lunar orbit is 3.8 × 10 8 m.

Answer 1

Hey !!

(a) | em / m | = | f₀ / fe |

f₀ = Focal length of objective

fe = Focal length of eyepiece

| m | = 15 × 100 / 1 = 1500

∵ image formed is inverted

 ∵ Angular magnification = + 1500

(b) Angle subtended by moon at object = angle of image at objective

          D/R = d/f₀

3.4 × 10⁶ / 3.8 × 10⁸ = d/15

d = 3.4/3.8 × 10⁻² × 15 m

d = 13.4 cm ( FINAL RESULT )

GOOD LUCK !!