If an object is placed symmetrically between two plane mirrors, inclined at an angle of $72^{\circ},$ then the total number of images formed is

The figure shows a ray of light as it travels from medium $A$ to medium $B$. The refractive index of medium $B$ relative to medium $A$ is:

$A$ ray of light is incident obliquely on a glass slab. Draw a ray diagram showing the path of the light ray. Clearly,mark the angle of incidence,angle of refraction,angle of emergence,and lateral displacement of the ray. Give a formula to find the refractive index of the glass slab in terms of the angle of incidence and the angle of refraction.

$A$ convex mirror has a focal length $f$. $A$ real object is placed at a distance $f$ in front of it. The mirror produces an image at

Where is the image formed when an object is placed at the principal focus $(F)$ in front of a convex lens?

What is the focal length of the objective of an astronomical telescope as compared to that of the eyepiece?