The focus of a plane mirror is considered to be at infinity because reflected rays do not converge or intersect. Unlike concave mirrors, which have a virtual focus where rays appear to diverge from a point behind the mirror, plane mirrors do not create a focal point in the same manner. When analyzing parallel rays reflecting off a plane mirror, they remain parallel and do not converge, reinforcing the concept of an infinite focal point. The discussion suggests that the terminology around "infinity" may be misleading, as it implies a paradox rather than a practical focal point. Ultimately, the nature of reflection in plane mirrors fundamentally differs from that in concave mirrors.
