Images Formed by Lenses
Describe the image formed by a lens.
- Incident light rays parallel to the principal axis of a thin convex (converging) lens will be refracted and converge toward a common location on the transmitted side of the lens, called the focal point.
- Incident light rays parallel to the principal axis of a thin concave (diverging) lens will be refracted and diverge as if they originated from a focal point on the incident side of the lens.
- A real image is formed by a lens when light rays originating from a common point are refracted such that they intersect at another common point.
- A virtual image is formed by a lens when refracted light rays diverge such that they appear to have originated from a common point.
- For a thin lens, the location of an image depends on the focal length of the lens and the distance between the object and the midline of the lens, as given by the thin-lens equation:
- The locations of a lens’s focal point, an object, and the image of the object formed by the lens follow sign conventions that are used to determine those locations relative to the lens itself.
- Lenses have a focal point on both sides of the lens that depends on the shape of the respective side of the lens.
- For a thin lens, the magnification of an image 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 lens. Relevant equation:
- Ray diagrams can be used to determine the location, type, size, and orientation of images formed by lenses.
- The three principal rays are typically used to find the images formed by lenses. The principal rays are 1) the ray parallel to the principal axis, 2) the ray that passes through the center of the lens where the principal axis intersects the lens, and 3) the ray that passes through the focal point of the lens.
- Images formed by a lens can be upright or inverted, virtual or real, and reduced, enlarged, or the same size as the object.