Question

Why the aperture of spherical mirror should be smaller than the centre of curvature , hijaabqueen :(​

Answer 1

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Spherical mirrors do not focus parallel light rays to a single focal point. The focus actually lies on a surface called a caustic... The point of using an aperture much smaller that the radius of the mirror is to restrict the incoming light to a region where rays do (almost) come to a single focal point