Images Formed by Mirrors
Describe the image formed by a mirror.
- Incident light rays parallel to the principal axis of a concave (converging) mirror will be reflected toward a common location, called the focal point.
- Incident light rays parallel to the principal axis of a convex (diverging) mirror will be reflected such that they appear to have originated from a common location behind the mirror, called the focal point.
- The focal point of a plane mirror is an infinite distance from the mirror.
- The focal point of a spherical mirror may be approximated as a point located on the principal axis of the mirror halfway between the surface of the mirror and the center of the mirror’s radius of curvature.
- A real image is formed by a mirror when light rays emanating from a common point are reflected and then intersect at a common point.
- A virtual image is formed by a mirror when reflected light rays diverge such that they appear to have originated from a common point.
- The location of an image depends on the focal length of the mirror and the distance between the object and the surface of the mirror. Relevant equation:
- The locations of a mirror’s focal point, an object near the mirror, and the image of the object formed by the mirror follow sign conventions that are used to determine those locations relative to the mirror itself.
- The distance between the image formed and a plane mirror is equal to the distance between the object and the plane mirror.
- The magnification of an image formed by a mirror is the ratio of the size of the image produced to the size of the object itself and depends on the locations of the object and image relative to the mirror. Relevant equation:
- Ray diagrams can be used to determine the location, type, size, and orientation of images formed by mirrors.
- The three principal rays are typically used to find the images formed by mirrors. The principal rays are 1) the ray parallel to the principal axis, 2) the ray that reflects at the center of the mirror where the principal axis intersects the mirror, and 3) the ray that passes through the focal point of the mirror.
- Images formed by a mirror can be upright or inverted, virtual or real, and reduced, enlarged, or the same size as the object.
AP Physics 2 limits the study of mirrors to plane mirrors, convex spherical mirrors, and concave spherical mirrors.