Light rays passing through a prism will be bent toward the:

• A. Apex
• B. Center
• C. Vertex
• D. Base

Answer: (D)

When light moves between materials with different optical densities, it changes direction—a process called refraction. In a triangular prism, the entering surface is inclined so that the normal points toward the base (the side opposite the apex). Going from air (lower index) into glass (higher index), the ray bends toward the normal. Because of the surface orientation, this refraction steers the light toward the base inside the prism. (On the way out, it bends again in the opposite direction, but the common statement about a prism describes the initial bend as toward the base.) That’s why the light rays are said to be bent toward the base.