In an astronomical telescope,how is the focal length of the objective lens compared to the focal length of the eyepiece?

The angle between an incident ray and the reflected ray is $70^{\circ}$ as shown in the figure. What is the value of $\theta$?

Which type of mirror can produce a virtual image?

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of $15\, cm$ from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

Where is the image formed when an object is placed between the principal focus $(F)$ and the center of curvature $(C)$ of a concave mirror?

Where should an object be placed in front of a concave mirror to obtain an inverted and magnified image?