Describe a spherical mirror.

The image formed by a concave mirror is real and of the same size. Where is the object placed?

Why does a light ray incident on a rectangular glass slab immersed in any medium emerge parallel to itself? Explain.

What is the focal length of a convex lens having power $+5.0 \,D$?

Where should an object be placed so that a real and inverted image of the same size is obtained by a convex lens?

Identify the device used as a spherical mirror or lens in the following cases,where the image formed is virtual and erect in each case.
$(a)$ Object is placed between the device and its focus,image formed is enlarged and behind it.
$(b)$ Object is placed between the focus and the device,image formed is enlarged and on the same side as that of the object.
$(c)$ Object is placed between infinity and the device,image formed is diminished and between the focus and optical centre on the same side as that of the object.
$(d)$ Object is placed between infinity and the device,image formed is diminished and between the pole and focus,behind it.