Question

what is principal axis?​

Answer 1

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what is principal axis?

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principal axis - a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted; "in a normal eye the optic axis is the direction in which objects are seen most distinctly" optic axis. axis - a straight line through a body or figure that satisfies certain conditions.

Answer 2

Answer:

The line passing through the optical centre and centres of curvature of the faces of a lens or a curved mirror

(or)

Any of three mutually perpendicular axes about which the moment of inertia of a body is maximum