American Buddhismâs numbers are booming. Published just over three years ago, an American Religious Identification Survey survey showed that from the years 1990 to 2000, Buddhism grew 170 percent in North America.
However, for a lens, a positive image distance implies that the image is located on the opposite side as the object. Virtual images are formed by concave lenses or by placing an object inside the focal length of a convex lens. The ray-tracing exercise is repeated for the case of a virtual image. In this case the virtual image is upright and shrunken. The same formula for the image and object distances used above applies again here.
As is easily demonstrated, in the paraxial approximation, the focal length of a convex mirror is half of its radius of curvature. Figure 74: The virtual focus of a convex mirror. There are, again, two alternative methods of locating the image formed by a convex mirror. The first is graphical, and the second analytical. According to the graphical method, the image produced by a convex mirror can always be located by drawing a ray diagram according to four simple rules: 1  An incident ray which is parallel to the principal axis is reflected as if it came from the virtual focus of the mirror.