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Last updated date: 23rd Nov 2023
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What are the new cartesian sign conventions used for concave lens and convex lens?

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Hint:A Cartesian sign convention is a set of rules in ray optics which are used to determine the signs of various distances measured in image formation through concave lens and convex lens such as object distance, image distance and focal length of the lens system.

The new Cartesian sign convention which are used for concave lens and convex lens area as follows:
-Focal length measured of concave lens is always negative while focal length of convex lens is taken as positive.
-The incident ray of light is always taken from left side to right side as the object in front of the lens is always kept at the left side of the lens.
-All the distances which are measured from the optical centre of the lens to the right are taken as positive while distances measured to the left of the optical centre are taken as negative.
-All distances are measured from the optical centre of the lens.

So for concave lens:
-Focal length is negative.
-Object distance is negative.
-Image distance depends upon whether the image is formed right to the optical centre or left to the optical centre.
For Convex lens:
-Focal length is positive.
-Object distance is negative.
-Image distance depends upon whether the image is formed right to the optical centre or left to the optical centre.

Note:It must be remembered that, these new sign conventions are depend upon the basic rule that the distances which are measured in the direction of light ray is taken as positive and while the distances which are measured in the opposite direction to that of light ray is taken as negative.