Geometrical OpticsEasy

Question

Focal length of the objective and eye-piece of an astronomical telescope are 20 cm and 10cm. If final image is at the minimum distance of clear vision. then length of the tube will be:-

Options

A.27.1 cm
B.25 cm
C.30 cm
D.None

Solution

for eye-piece
Ue = - 7.1 cm
so length of the tube
L = |f0| + |ue| = 20 + 7.1 = 27.1cm

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