Because the index of refraction of the lens is greater than that of air, the ray moves toward the perpendicular as it enters and away from the perpendicular as it leaves.
An expanded view of the path of one ray through the lens is shown in Figure 16.25 to illustrate how the ray changes direction both as it enters and as it leaves the lens. Such a lens is called a converging lens because of the converging effect it has on light rays. The central axis, or axis, is defined to be a line normal to the lens at its center. The convex lens shown in Figure 16.25 has been shaped so that all light rays that enter it parallel to its central axis cross one another at a single point on the opposite side of the lens. Concave, convex, focal point F, and focal length f have the same meanings as before, except each measurement is made from the center of the lens instead of the surface of the mirror. Some of what we learned in the earlier discussion of curved mirrors also applies to the study of lenses. In this section, we use the law of refraction to explore the properties of lenses and how they form images. Lenses are found in a huge array of optical instruments, ranging from a simple magnifying glass to the eye to a camera’s zoom lens. Review the terms focal point, focal length, object distance, image distance, concave, convex, converging, and diverging from the Reflection section.
Review the lens/mirror equation from the Reflection section.
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