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Magnification Image Size The image produced by a lens is typically a different size than the object. An object and image are image measured by relative distance. • Distance from the lens s • Distance in plane y yo so object si yi Inverted Image Images in a single convex lens are inverted. • Negative planar distance • yi < 0 image Images can have negative distance from the lens. • Virtual image yo so object si yi Magnification Ratio The ratio of the image size to image yo so si yi the object size is the magnification M. • Negative for inverted images From geometry this equivalent to the ratio of the image distance to the object distance. object yi si M yo so Single Lens A single converging lens will image magnify objects. • Always inverts yo si so yi A real image requires a positive object distance. • so > f object A real image requires a 1 1 1 s o si f M yi s i yo so positive image distance. • si > f Photocopier A photocopier needs to create an image exactly the same size as the object. • Object at twice focal length yi Myo 1yo M 1 si so 1 1 2 1 so so so f si so 2 f si so Projector si M so 1 1 M 1 1 so Mso Mso f so M 1 f M A projector needs a larger image at a distant screen. • Real image • Inverted object • Object between f and 2f Magnifying Glass A magnifying glass works on objects within the focal length. • Upright virtual image • Eye needed to focus si M 3 so 1 1 2 1 s o 3 s o 3s o f 2 so f 3 si 3so 2 f next