Summarizing Image Formation by Lenses

Image Formation by Lenses Summary

• Light rays entering a converging lens parallel to its axis cross one another at a single point on the opposite side.
• For a converging lens, the focal point is the point at which converging light rays cross; for a diverging lens, the focal point is the point from which diverging light rays appear to originate.
• The distance from the center of the lens to its focal point is called the focal length \(f\).
• Power \(P\) of a lens is defined to be the inverse of its focal length, \(P=\cfrac{1}{f}\).
• A lens that causes the light rays to bend away from its axis is called a diverging lens.
• Ray tracing is the technique of graphically determining the paths that light rays take.
• The image in which light rays from one point on the object actually cross at the location of the image and can be projected onto a screen, a piece of film, or the retina of an eye is called a real image.
• Thin lens equations are \(\cfrac{1}{{d}_{\text{o}}}+\cfrac{1}{{d}_{\text{i}}}=\cfrac{1}{f}\) and \(\cfrac{{h}_{\text{i}}}{{h}_{\text{o}}}=-\cfrac{{d}_{\text{i}}}{{d}_{\text{o}}}=m\) (magnification).
• The distance of the image from the center of the lens is called image distance.
• An image that is on the same side of the lens as the object and cannot be projected on a screen is called a virtual image.

Glossary

converging lens

a convex lens in which light rays that enter it parallel to its axis converge at a single point on the opposite side

diverging lens

a concave lens in which light rays that enter it parallel to its axis bend away (diverge) from its axis

focal point

for a converging lens or mirror, the point at which converging light rays cross; for a diverging lens or mirror, the point from which diverging light rays appear to originate

focal length

distance from the center of a lens or curved mirror to its focal point

magnification

ratio of image height to object height

power

inverse of focal length

real image

image that can be projected

virtual image

image that cannot be projected