What is meant by the radius of curvature of a spherical mirror? How is it related to the focal length of the mirror?

At what distance should an object be placed to obtain its real,inverted and of same size image as the object by a convex lens?

Define linear magnification produced by a spherical mirror. Also,give its relation.

Where is the image formed when an object is placed anywhere in front of a concave lens?

State the relation between object distance,image distance,and focal length of a concave or convex mirror. $A$ concave mirror produces a two times magnified real image of an object placed at $10 \ cm$ from it. Find the position of the image.

$(i)$ Describe an activity to find the approximate value of the focal length of a concave mirror.
$(ii)$ What happens to the size of the image of an object when it is moved gradually away from a convex mirror?
$(iii)$ In an experiment to study refraction through a glass slab,it is observed that a ray of light undergoing refraction emerges parallel to the direction of the incident ray. Why does it happen so? Explain with the help of a diagram.