keratometer measures the magnification of the image. The smaller the magnification, the smaller the radius of curvature of the cornea. If the light source is 12.0 cm from the cornea and the image’s magnification is 0.0320, what is the cornea’s radius of curvature?
CONCAVE MIRRORS Object position image type magnification d 0 >R real, inverted reduced (m<1) R<d 0 <f real, inverted enlarged (m>1) d 0 <f Virtual, upright enlarged (m>1) m is the absolute value of the magnification factor.
CONVEX MIRROR Object location image type magnification d 0 >R Virtual, upright reduced (m<1) R<d 0 <f Virtual, upright reduced (m<1) d 0 <f Virtual, upright reduced (m<1) m is the absolute value of the magnification factor.
LENSES Spherical lenses have surfaces defined by two spheres, and the surfaces are either convex or concave
CONVERGING AND DIVERGING LENSES Converging or biconvex lenses ( with both surfaces convex ) have a positive focal length Converging lenses are thickest at the middle. Diverging or biconcave lenses ( with both surfaces concave ) have a negative focal length. Diverging lenses are thickest at the edges.
CONVERGING LENS Rays of light entering a converging lens parallel to its axis converge at its focal point F . (Ray 2 lies on the axis of the lens.) The distance from the center of the lens to the focal point is the lens’s focal length 𝑓 . An expanded view of the path taken by ray 1 shows the perpendiculars and the angles of incidence and refraction at both surfaces.
MAGNIFYING GLASS Sunlight focused by a converging magnifying glass can burn paper . Light rays from the sun are nearly parallel and cross at the focal point of the lens. The more powerful the lens, the closer to the lens the rays will cross.