The diameter of the moon is `3.5 xx 10^(3) km` and its distance from the earth is `3.8 xx 10^(5)km`. It is seen through a telescope having focal lengths of objective and eye-piece as `4m` and `10 cm` respectively. Calculate (a) magnifying power of telescope (b) length of telescope tube and (c) anngular size of image of moon.

Explanation

`MP = (f_(0))/(f_(e)) = -(400)/(10) = -40` . Angle subtended by the moon at the objective = `(3.5xx10^(3))/(3.8 xx 10^(5)) = 0.009 "radian"`.
Thus angular diameter of the image = `MP xx "visual angle" = 40 xx 0.009 = 0.36 "radian" = (0.36 xx 180)/(3.14) = 21^(@)`