Ray Diagram Basics for Spherical Mirrors

To determine the location of an image formed by a spherical mirror (concave or convex) using a ray diagram, we rely on the principles of reflection. The image is formed at the point where the reflected rays actually intersect (for real images) or appear to diverge from (for virtual images).

Minimum Reflected Rays Required

While using multiple rays can help confirm the image location and characteristics, only two reflected rays are fundamentally necessary to pinpoint the image's position. The intersection point of these two rays defines where the image is formed.

• Ray 1: Draw a ray from the object parallel to the principal axis. After reflection, this ray passes through the focal point (F) for a concave mirror or appears to diverge from the focal point (F) for a convex mirror.
• Ray 2: Draw another ray from the object through the center of curvature (C). This ray strikes the mirror normally and reflects back along the same path.

The point where these two reflected rays (or their extensions) intersect is the location of the image.

Why Two Rays Suffice

Every point on the object emits rays in all directions. By selecting two specific, predictable rays (like the ones described above, or others like a ray hitting the pole or passing through the focus), we can trace their paths after reflection. Since geometry dictates that two intersecting lines define a unique point, the intersection of just two reflected rays is sufficient to locate the image corresponding to the point from which those rays originated on the object.