In a Galilean telescope,if the powers of an objective and eye lens are respectively $+1.25 \, D$ and $-20 \, D$,then for relaxed vision,the length and magnification will be

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 focal length of the objective and eye lens of an astronomical telescope are $2 \, m$ and $5 \, cm$ respectively. The final image is formed at $(i)$ the least distance of distinct vision and $(ii)$ infinity. The magnifying power in both cases will be:

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

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 an astronomical telescope,the focal lengths of two lenses are $180 \, cm$ and $6 \, cm$ respectively. In normal adjustment,the magnifying power will be