A. Images formed with plane mirrors
Images with mirrors are formed when many nonparallel rays from a given point on a source are reflected from the mirror surface, converge, and form a corresponding image point. When this happens, point by point for an extended object, an image of the object, point by point, is formed. Image formation in a plane mirror is illustrated in several sketches shown in Figure 3-14.
In Figure 3-14a, point object S sends nonparallel rays toward a plane mirror, which reflects them as shown. The law of reflection ensures that pairs of triangles like SNP and S′NP are equal, so that all reflected rays appear to originate at the image point S′, which lies along the normal line SN, and at such depth that the image distance S′N equals the object distance SN. The eye sees a point image at S′ in exactly the same way it would see a real point object placed there. Since the actual rays do not exist below the mirror surface, the image is said to be a virtual image. The image S′ cannot be projected on a screen as in the case of a real image. An extended object, such as the arrow in Figure 3-14b, is imaged point by point by a plane mirror surface in similar fashion. Each object point has its image point along its normal to the mirror surface and as far below the reflecting surface as the object point lies above the surface. Note that image position does not depend on the position of the eye.
The construction in Figure 3-14b also makes clear that the image size is identical to the object size, giving a magnification of unity. In addition, the transverse orientations of object and image are the same. A right-handed object, however, appears left-handed in its image. In Figure 3-14c, where the mirror does not lie directly below the object, the mirror plane may be extended to determine the position of the image as seen by an eye positioned to receive reflected rays originating at the object. Figure 3-14d illustrates multiple images of a point object O formed by two perpendicular mirrors. Each image, I and I2, results from a single reflection in one of the
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