Principal axis is the: a. straight line drawn from the center of curvature to the mid point of the mirror.
b. straight line drawn from the center of curvature to a point on the outer edge of the mirror.
c. straight line drawn from the center of curvature to any point of the mirror.
d. straight line joining any two points on the mirror.
e. None of the other answers given is correct.

d. straight line joining any two points on the mirror

Explanation:

Principal axis is the straight line that passes through the center of a mirror, which is also perpendicular to the surface of the mirror.

The principal axis connects the principal focus and the center of curvature of the mirror. In other words, it is a straight line or axis on which the center of curvature and principal focus can be found. The principal axis joins these two points; the center of curvature and principal focus.

Therefore, the correct option is "D"

d. straight line joining any two points on the mirror

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hope this : )

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