# radius of curvature

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## radius of curvature

(**ray**-dee-us) Symbol:

*r*,

*R*. The radius of the sphere whose surface contains the surface of a spherical mirror, lens, or wavefront. The

*curvature*of the mirror, etc., is given by the reciprocal of the radius of curvature, i.e. by 1/

*r*. The radius of curvature of a mirror is twice its focal length,

*f*. That of a lens is given by

1/

where *f*= (*n*– 1)(1/*r*_{1}– 1/*r*_{2})*n*is the refractive index; it is assumed that, in the direction of light travel, the radii,

*r*

_{1}and

*r*

_{2}, for the convex and concave lens surfaces are positive and negative, respectively.

## radius of curvature

[′rād·ē·əs əv ′kər·və·chər] (mathematics)

The radius of the circle of curvature at a point of a curve.

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