Mirror Equation and Magnification
The Gaussian mirror equation, also known as the mirror and lens equation, relates the object distance and image distance to the focal length :
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The sign convention used here is that the focal length is positive for concave mirrors and negative for convex ones, and and are positive when the object and image are in front of the mirror, respectively. (They are positive when the object or image is real.)
For convex mirrors, if one moves the term to the right side of the equation to solve for, the result is always a negative number, meaning that the image distance is negative—the image is virtual, located "behind" the mirror. This is consistent with the behavior described above.
For concave mirrors, whether the image is virtual or real depends on how large the object distance is compared to the focal length. If the term is larger than the term, is positive and the image is real. Otherwise, the term is negative and the image is virtual. Again, this validates the behavior described above.
The magnification of a mirror is defined as the height of the image divided by the height of the object:
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By convention, if the resulting magnification is positive, the image is upright. If the magnification is negative, the image is inverted (upside down).
Read more about this topic: Convex Mirror, Analysis
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