A paraxial ray parallel to the principal axis falls on a concave spherical mirror. After reflection, the ray passes through which point? 
AThe centre of curvature
BThe pole
CThe principal focus
DThe focal plane at infinity
Answer & Solution
Correct answer: C. The principal focus
For a concave mirror, paraxial rays parallel to the principal axis converge after reflection at the principal focus. This is one of the standard rules used in drawing ray diagrams for image formation.
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