State and explain the New Cartesian Sign Convention for spherical lenses.
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New Cartesian Sign Convention gives the sign of variables to be used when using the lens formula for spherical lenses.
According to the rules:
(i) All the distances are measured from the optical centre of the lens.
(ii) The distances to the right of the lens are taken as positive.
(iii) The distances to the left of the lens are taken as negative.
(iv) The distances upwards to the principal axis are taken as positive.
(v) The distances downwards to the principal axis are taken as negative.