Online Encyclopedia

CONVEX

Online Encyclopedia
Originally appearing in Volume V23, Page 4 of the 1911 Encyclopedia Britannica.
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CONVEX MIRROR Position of Object. Position of Image. Character of Image. to Between co and A A The above discussion of spherical mirrors assumes that the mirror has such a small aperture that the reflected rays from any point unite in a point. This, however, no longer holds when the mirror has a wide aperture, and in general the reflected rays envelop a caustic (q.v., see also ABERRATION). The only mirror which can sharply reproduce an object-point as an image-point has for its section an ellipse, which is so placed that the object and image are at its foci. This follows from a property of the curve, viz. the sum of the focal distances is constant, and that the focal vectores are equally inclined to the normal at the point. More important than the elliptical mirror, however, is the parabolic, which has the property of converting rays parallel to,the axis into a pencil through its focus; or, inversely, rays from a source placed at the focus are converted into a parallel beam; hence the use of this mirror in search-lights and similar devices.
End of Article: CONVEX
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