If the angular magnification of an astronomical telescope is 42 and the diameter of the objective is 72 mm, what is the minimum diameter of the eyepiece required to collect all the light entering the objective from a distant point source located on the telescope axis?

Minimum diameter=1.714

Explanation:

Angular magnification=fob/fey=42

fob=40*fey

Hence minimum diameter=diameter of objective/angular magnification

minimum diameter=72/42=1.714

total distance travelled = 60 miles

total time taken =1.5 hours

average speed = total distance / total time

60 / 1.5

= 40

therefore, average speed = 40 m/h

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