Question
The focal length of a concave mirror is 20 cm. Where
should an object be placed to get an image of the same size?Solution
For a concave mirror, an image equal in size and real is formed when the object is placed at the center of curvature. The center of curvature is at a distance 2f = 40 cm, so half that is 20 cm from the mirror. At this position, image is real, inverted, and same size. Hence, the correct position is at 20 cm.
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