When an object is placed in front of a concave mirror, and image is formed at a point where at least two reflected rays intersect each other. The various rules employed for obtaining images on a concave mirror are: A ray of light parallel to the principle axis of a concave mirror passes through its principle focus after reflection from the mirror. A ray of light passing through the centre of curvature of a concave mirror is reflected back along the same path. A ray of light passing through the focus of a concave becomes parallel to the principle axis after reflection from the mirror.