Question

(i) 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 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 `3.48xx10^(6)m`, and the radius of lunar orbit is `3.8xx10^(8) m`.

Answer 1

Angular magnification is given by
`m_(0)=|f_(0)/(fe)|=(1500)/1=1500`
Diameter of the image of moon formed by the objective lens is = d
`d = ("Diameter of the moon")/("Radius of lunar orbit")xxf_(0)`
`d=(3.48xx10^(6)xx15)/(3.8xx10^(8))`
`d = 0.1373m`
`d = 13.73 cm`