Question

Define principal axis for lens

Answer 1

Answer:

optics. Optical axis, the straight line passing through the geometrical centre of a lens and joining the two centres of curvature of its surfaces. Sometimes the optical axis of a lens is called its principal axis. The path of a light ray along this axis is perpendicular to the surfaces and, as such, will be unchanged.

Answer 2

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$\bigstar$ Principal axis is the straight line passing through the geometrical centre of a lens and joining the two centres of curvature of its surfaces.