How do you identify the focal point in focal length of concave mirror?

What is focal length ?

How do you identify pellagra?

What is called a focal point of a concave mirror ?

What is the role of sun rays in finding the focal point of the concave mirror ?

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

What is the relation between radius of curvature and focal length of a concave mirror ?

A concave mirror produces an image of a long vertical pin, placed 40 cm from the mirror, at the position of the object. Find the focal length of the mirror.