What is the tube length of a telescope?

If a telescope is reversed,i.e.,viewed from the objective side,what happens to the appearance of the object?

The magnifying power of a refracting type of astronomical telescope is $m$. If the focal length of the eyepiece is doubled,then the magnifying power will become:

The magnifying power of a telescope is high if its objective and eyepiece have respectively

In a simple telescope,the focal length of the objective lens is $f_o = 60 \ cm$ and the focal length of the eyepiece is $f_e = 5 \ cm$. If the rays coming from the object make an angle of $2^\circ$ at the objective,then the angular magnification (angular size of the image) is ........... $^\circ$.

$A$ small telescope has an objective lens of focal length $140 \; cm$ and an eyepiece of focal length $5.0 \; cm$. What is the magnifying power of the telescope for viewing distant objects when
$(a)$ the telescope is in normal adjustment (i.e.,when the final image is at infinity)?
$(b)$ the final image is formed at the least distance of distinct vision $(25 \; cm)$?