Question

What is principal axix
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Answer 1

Answer:

each of three mutually perpendicular axes in a body about which the moment of inertia is at a maximum.

It is also known as optical axis

Explanation:

An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens or microscope. The optical axis is an imaginary line that defines the path along which light propagates through the system, up to first approximation.