2 minute read
Mirror Images
by AudioLearn
Figure 144.
The image will be magnified when the size of the image past the lens is greater than the actual image as light from it passes through the lens. Real images, such as those produced by a movie projector, are formed by converging lenses and when an object is further away from the lens than its focal length. The image will be inverted by a converging lens when the object being looked at is further away than the focal length of the lens as is seen in figure 144. A virtual image is an image on the same side of the lens as the object and cannot be projected onto a screen. This will be an upright image and will be seen in convex lenses used to treat nearsightedness.
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MIRROR IMAGES
Images seen in flat mirrors are the same size as the object and will be seen as being “behind the mirror”. A variety of images can be gotten from a mirror, including magnification of an image in makeup mirrors and rear-view mirrors of automobiles. Security mirrors do the opposite, forming small images compared to the object. Each of these phenomena can be explained by the law of reflection. The image seen in a mirror is considered a virtual image because it cannot be projected. This is obvious because, if you walk behind a mirror, you cannot see the image.
Concave mirrors are mirrors that are small compared to their radius of curvature, acting similar to a parabolic mirror. They act very much like the “thin lens” that best
approximates a perfect lens but is not perfect. These small, concave mirrors will have a fairly well-defined focal point at a distance from the center of the mirror. The focal length will be positive as these are considered converging mirrors. Figure 145 shows a converging mirror:
Figure 145.
The shorter the focal length, the more powerful the mirror is with power being one divided by the focal length. The more curved the mirror, the greater is its power because it will have a short focal length. The focal length, using simple geometry and the laws of reflection, is half the radius of curvature of the mirror.
Convex mirrors are diverging mirrors, in which the light from the mirror appears to originate from a focal point behind the mirror. Both the focal length and power of the mirror will be negative as is the case with diverging lenses. The rules of ray tracing and the law of reflection apply to determining what these images look like when an object is placed in front of the mirror. Figure 146 shows a diverging or convex mirror:
