(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`.

Explanation

Angular magnification
`=-(f_(0))/(f_(e))(1+(f_(e))/(D))`
`=-(1500)/(1)(1+(1)/(25))`
`=-1560`

Negative sign indicates that the image is inverted.
Diameter of the image of the moon formed by the objective lens=d
`tan alpha approx alph=("diameter of the moon")/("radius of the orbit")=(d)/(f_(0))=(3.42xx10^(6))/(3.8xx10^(8))=(d)/(15)Rightarrow d=0.135m`