If the image formed by a convex lens is of the same size as that of the object,what is the position and nature of the image with respect to the lens?

What can be measured using a dioptre meter?

Draw the ray diagram in each case to show the position,nature,and size of the image formed when the object is placed:
$(i)$ At the centre of curvature of a concave mirror.
$(ii)$ Within the focal length of a convex lens.
$(iii)$ Between the pole and focus of a concave mirror.
$(iv)$ In front of a convex mirror.
$(v)$ In front of a concave lens.

$A$ diminished virtual image can be obtained only in

How will you distinguish between a convex and a concave lens without touching them?

What is the angle of incidence for a light ray incident on a glass slab such that it does not undergo refraction (in $^{\circ}$)?