In a reflecting telescope,a secondary mirror is used to:

Four convergent lenses have focal lengths $100 \, cm, 10 \, cm, 4 \, cm$ and $0.3 \, cm$. For a telescope with maximum possible magnification,we choose the lenses of focal length

$A$ small telescope has an objective lens of focal length $140 \ cm$ and an eyepiece of focal length $5 \ cm$. The magnifying power of the telescope for viewing a distant object when the telescope is in normal adjustment is . . . . . . .

To increase the magnifying power of a telescope ($f_o$ = focal length of the objective and $f_e$ = focal length of the eye lens):

This question has Statement-$1$ and Statement-$2$. Of the four choices given after the Statements,choose the one that best describes the two Statements.
Statement-$1$: Very large size telescopes are reflecting telescopes instead of refracting telescopes.
Statement-$2$: It is easier to provide mechanical support to large size mirrors than large size lenses.

In normal adjustment,for a refracting telescope,the distance between the objective and the eyepiece is $30\,cm$. The focal length of the objective,when the angular magnification of the telescope is $2$,will be $.....\,cm$.