Convex Spherical Mirrors

Regardless of the position of the object reflected by a convex mirror, the image formed is always virtual, upright, and reduced in size. This interactive tutorial explores how moving the object farther away from the mirror's surface affects the size of the virtual image formed behind the mirror.

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The tutorial initializes with the object (an upright arrow) positioned with its tail touching the center of the mirror's optical axis on the front side of the mirror, far away from the center of curvature and the focal point (located behind the mirror). To operate the tutorial, use the Object Position slider to translate the arrow back and forth in front of the mirror. As the arrow approaches the mirror, the upright, real image grows larger, approaching the size of the arrow, but becomes much smaller as the arrow is moved farther away from the reflecting surface of the mirror.

The convex mirror has a reflecting surface that curves outward resembling a portion of the exterior of a sphere. Light rays parallel to the optical axis are reflected from the surface in a manner that diverges from the focal point, which is behind the mirror. Images formed with convex mirrors are always right side up and reduced in size. These images are also termed virtual images, because they occur where reflected rays appear to diverge from a focal point behind the mirror.

Convex mirrors are often used in automobile right-hand rear-view applications where the outward mirror curvature produces a smaller, more panoramic view of events occurring behind the vehicle. When parallel rays strike the surface of a convex mirror, they are reflected outward and diverge away from the mirrored surface. When the brain retraces the rays they appear to come from behind the mirror where they would converge, producing a smaller upright image (the image is upright since the virtual image is formed before the rays have crossed the focal point). Convex mirrors are also used as wide-angle mirrors in hallways and businesses for security and safety. The most amusing applications for curved mirrors are the novelty mirrors found in state fairs, carnivals, and fun houses. These mirrors often incorporate a mixture of concave and convex surfaces, or surfaces that gently change curvature, to produce bizarre, distorted reflections when people observe themselves.

Contributing Authors

Matthew J. Parry-Hill, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.