Definition of Foci. Meaning of Foci. Synonyms of Foci

Here you will find one or more explanations in English for the word Foci. Also in the bottom left of the page several parts of wikipedia pages related to the word Foci and, of course, Foci synonyms and on the right images related to the word Foci.

Definition of Foci

Foci
Focus Fo"cus, n.; pl. E. Focuses, L. Foci. [L. focus hearth, fireplace; perh. akin to E. bake. Cf. Curfew, Fuel, Fusil the firearm.] 1. (Opt.) A point in which the rays of light meet, after being reflected or refrcted, and at which the image is formed; as, the focus of a lens or mirror. 2. (Geom.) A point so related to a conic section and certain straight line called the directrix that the ratio of the distace between any point of the curve and the focus to the distance of the same point from the directrix is constant. Note: Thus, in the ellipse FGHKLM, A is the focus and CD the directrix, when the ratios FA:FE, GA:GD, MA:MC, etc., are all equal. So in the hyperbola, A is the focus and CD the directrix when the ratio HA:HK is constant for all points of the curve; and in the parabola, A is the focus and CD the directrix when the ratio BA:BC is constant. In the ellipse this ratio is less than unity, in the parabola equal to unity, and in the hyperbola greater than unity. The ellipse and hyperbola have each two foci, and two corresponding directrixes, and the parabola has one focus and one directrix. In the ellipse the sum of the two lines from any point of the curve to the two foci is constant; that is: AG+GB=AH+HB; and in the hyperbola the difference of the corresponding lines is constant. The diameter which passes through the foci of the ellipse is the major axis. The diameter which being produced passes through the foci of the hyperbola is the transverse axis. The middle point of the major or the transverse axis is the center of the curve. Certain other curves, as the lemniscate and the Cartesian ovals, have points called foci, possessing properties similar to those of the foci of conic sections. In an ellipse, rays of light coming from one focus, and reflected from the curve, proceed in lines directed toward the other; in an hyperbola, in lines directed from the other; in a parabola, rays from the focus, after reflection at the curve, proceed in lines parallel to the axis. Thus rays from A in the ellipse are reflected to B; rays from A in the hyperbola are reflected toward L and M away from B. 3. A central point; a point of concentration. Aplanatic focus. (Opt.) See under Aplanatic. Conjugate focus (Opt.), the focus for rays which have a sensible divergence, as from a near object; -- so called because the positions of the object and its image are interchangeable. Focus tube (Phys.), a vacuum tube for R[oe]ntgen rays in which the cathode rays are focused upon the anticathode, for intensifying the effect. Principal, or Solar, focus (Opt.), the focus for parallel rays.

Meaning of Foci from wikipedia

- Look up focus or foci in Wiktionary, the free dictionary. Focus (pl.: foci or focuses) may refer to: Focus or Focus Festival, former name of the Adelaide...
- or foci (/ˈfoʊkaɪ/; sg.: focus) are special points with reference to which any of a variety of curves is constructed. For example, one or two foci can...
- Aberrant crypt foci (ACF) are clusters of abnormal tube-like glands in the lining of the colon and ****. Aberrant crypt foci form before colorectal...
- A focus of infection is a place containing whatever epidemiological factors are needed for transmission of an infection. Any focus of infection will have...
- A hypocenter or hypocentre (from Ancient Gr**** ὑπόκεντρον (hupókentron) 'below the center'), also called ground zero or surface zero, is the point on the...
- further used on occasion to describe other curves having two singular points (foci), such as ellipses, hyperbolas, and C****ini ovals. However, the term bipolar...
- in the plane such that the product of the distances to two fixed points (foci) is constant. This may be contrasted with an ellipse, for which the sum of...
- Bernoulli is a plane curve defined from two given points F1 and F2, known as foci, at distance 2c from each other as the locus of points P so that PF1·PF2...
- points, the product of whose distances from two fixed points, the curves' foci, is a constant. Under very particular cir****stances (when the half-distance...
- locus of points such that the sum of the distances to two fixed points (the foci) is constant. The second theorem is that for any conic section, the distance...