The measurements from _______________ are taken for the spherical lenses according to sign conventions.

Correct option is A

The correct answer is (a) Optical centre.
· For spherical lenses, measurements are taken from the optical centre of the lens according to sign conventions. The optical center is the point on the lens where the principal axis intersects, and it serves as the reference point for measuring distances in lens formulas.
Information Booster:
· Pole: This term is more commonly used in the context of spherical mirrors rather than lenses.
· Principal focus: This is a focal point of the lens but is not the reference point for measurements in sign conventions.
· Both Principal focus and pole: Incorrect, as only the optical center is used as the reference point in lenses.