Question

Why does a ray incident on a concave mirror parallel to is principal axis passes through the focus ?

Answer 1

Dear student The answer is hidden in centre of curvature. As we know that when a ray passes through center of curvature it falls back. It happens as it is a centre of sphere , which act as normal to circumference (concave mirror). So when a ray incident parallel to principal axis it passes through focus because here the normal for the incident ray and reflected ray is the line connecting the point of incidence and the center of curvature so, according the law of reflection the angle of incidence is = angle of reflection. Regards