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xinlan

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## Homework Statement

On one of the shelves in your physics lab is displayed an antique telescope. A sign underneath the instrument says that the telescope has a magnification of 20 and consists of two converging lenses, the objective and the eyepiece, fixed at either end of a tube 60.0 cm long. Assuming that this telescope would allow an observer to view a lunar crater in focus with a completely relaxed eye, what is the focal length Fe of the eyepiece?

## Homework Equations

Length (L) = Fo+Fe

Which Fo = Focal length of the objective lens

Fe = Focal length of the eyepiece

M = -Fo/Fe

## The Attempt at a Solution

L = Fo+Fe

60 = Fo+Fe

Fe = 60-Fo

M = -Fo/Fe

20 = -(60-Fe) / Fe

Which Fe would be -3.16

But I got wrong..

Please help me..

thank you..