An astronomical telescope is made with lenses of focal lengths 80.0 and $2.00 \mathrm{~cm}$. What is the barrel length of this telescope?
A) $105 \mathrm{~cm}$
B) $82.0 \mathrm{~cm}$
C) $80.0 \mathrm{~cm}$
D) $78.0 \mathrm{~cm}$
E) $127 \mathrm{~cm}$

Question

Quizplus · Accepted Answer

The barrel length of an astronomical telescope in the normal adjustment (for viewing distant objects) is the sum of the focal lengths of the objective lens and the eyepiece. Therefore, the barrel length is $80.0 \mathrm{~cm} + 2.00 \mathrm{~cm} = 82.0 \mathrm{~cm}$.

An Astronomical Telescope Is Made with Lenses of Focal Lengths 2.00 cm2.00 \mathrm{~cm}2.00 cm

An Astronomical Telescope Is Made with Lenses of Focal Lengths $2.00 \mathrm{~cm}$