What are paraxial rays ?

What are canal rays?

What represents this ray diagram ?

What happens to a ray travelling parallel to the principal axis ?

What happens to a ray which passes through focal point and falls on the concave mirror and also draw the ray diagram.

What happens to a ray that is incident on a curved surface separating the two media ? Are the laws of refraction still valid ?

What happens when parallel rays of light fall on a lens making some angle with the principal axis ?