Explained: Cartesian Sign Convention for Mirrors

Let us study the Cartesian sign convention in the case of a concave mirror first:

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In this case, the object is always placed in front of the mirror, therefore, the object distance is taken as negative.

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The center of curvature & focus lies in front of the concave mirror, hence, the radius of curvature & focal length are taken as negative.

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The distance of the image is taken as negative when the image formed is in front of the concave mirror.

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If the image is formed behind the mirror, then the distance of the image is taken as positive.

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For an erect image, the height of the image is taken as positive. If the image is inverted, the height is taken as negative.

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Now, let us study the Cartesian sign convention in the case of a convex mirror:

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The object distance here is taken as negative as the object is placed in front of the mirror.

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The center of curvature and focus lies behind the mirror, hence radius of curvature and focal length are taken as positive.

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For a convex mirror, the image is always formed behind the mirror. Hence, the distance of the image is taken as positive.

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For a convex mirror, the image formed is always erect, thus the height of the image is taken as always positive.

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The Cartesian sign convention explained, is shown below:

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