If the focal length of the eyepiece of a telescope is doubled, its magnifying power $(m)$ will be

An observer looks at a tree of height $15 \ m$ with a telescope of magnifying power $10$. To him,the tree appears

$A$ 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 $(25 \; cm)$?

$A$ telescope has an objective lens of focal length $200 \, cm$ and an eyepiece with focal length $2 \, cm$. If this telescope is used to see a $50 \, m$ tall building at a distance of $2 \, km$,what is the height of the image of the building formed by the objective lens in $cm$?

The magnifying power of a telescope can be increased by

$A$ reflecting telescope utilizes