Question

A reflecting telescope is built with a $20cm$-diameter mirror having an$1.00$m focal length. It is used with an$10\times$eyepiece.

What are:

(a) the magnification?

(b) the $f‐number$of the telescope?

Short answer

(a). The magnification is $40$.

(b). The$f‐number$of the telescope is$5.0$.

Step-by-step solution

Part (a) Step 1: Given Information.

We need to find the magnification.

Part (a) Step 2: Simply.

$M_{eye}=\left(25cm\right)/f_{eye}$

$f_{eye}=25/10=2.5cm$

Therefore,

$M_{telesccope}=-f_{obj}/f_{eye}=100cm/2.5cm=40.$

Here $M_{eye}$magnification of the eye, $M_{telesccope}$is the magnification of a telescope,$f_{eye}$focal length of the eye.

Part (b) Step 1: Given Information.

We need find the f - number of telescope.

Part (b) Step 2: Simply.

$f-number=\frac{f}{D}=\frac{100cm}{20cm}=5.0$

Here $f$is focal length $D$is the diameter.