Mammoth Memory

Convex lens: principal axis

The principal axis of a convex lense is the "main" axis.

It is an imaginary line that is perpendicular (at 90 degrees) to the verticle axis and passes through the centre of curvatures (centre points of the spheres).

The main opera singer is the principal one

The principal opera singer is the main opera singer.


The word principal is used because it is the most important of all the possible axes. Compare this to the principal singer of an opera, who is the most important singer.

The principal axis of a lens

Here we have the principal axis in red.

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