Which symbol is used for the refractive index?

How will you decide whether a given piece of glass is a convex lens,concave lens,or a plane glass plate?

In which of the following,the image of an object placed at infinity will be highly diminished and point-sized?

What is the power of a convex lens with a focal length of $20 \text{ cm}$?

$(i)$ Define a real image of an object.
$(ii)$ Name the mirror that:
$(a)$ can give a real as well as a virtual image of an object.
$(b)$ will always give a virtual image of the same size as the object.
$(c)$ will always give a virtual and diminished image of an object.
$(d)$ is used by a doctor in examining teeth.
$(iii)$ With the help of a ray diagram,explain the use of a concave mirror as a solar concentrator.

When an object is placed between the principal focus $(F)$ and the center of curvature $(C)$ of a concave mirror,what kind of image is formed?