The length of a telescope is $36 \, cm$. The focal lengths of its lenses can be

Two convex lenses of focal lengths $0.3 \, m$ and $0.05 \, m$ are used to make a telescope. The distance kept between the two is .... $m$

$(a)$ $A$ small telescope has an objective lens of focal length $140\;cm$ and an eyepiece of focal length $5.0\;cm$. What is the separation between the objective lens and the eyepiece?
$(b)$ If this telescope is used to view a $100\;m$ tall tower $3\;km$ away,what is the height of the image of the tower formed by the objective lens?
$(c)$ What is the height of the final image of the tower if it is formed at $25\;cm$?

When the diameter of the aperture of the objective of an astronomical telescope is increased,its

$A$ Cassegrain telescope uses two mirrors as shown in the figure. Such a telescope is built with the mirrors $20 \; mm$ apart. If the radius of curvature of the large mirror is $220 \; mm$ and the small mirror is $140 \; mm$,where will the final image of an object at infinity be?

The angular magnification of an astronomical telescope is $10$. The final image is formed at infinity. The length of the telescope is $44 \, cm$. The focal length of the objective lens is .......... $cm$.