Question

What do you mean by principal focus and aperture with regard to spherical mirrors

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Answer 1

Principal focus:

It is a point on the principal axis, where the light rays appear to converge after reflection.

$F = \frac{R}{2}$

F = Principal focus

R = Radius of curvature

Aperture:

An aperture of a mirror from which the reflection of light actually takes place. Aperture helps us in finding out the size of the mirror.