Prism (geometry)

A polyhedron with two congruent parallel polygonal bases whose corresponding vertices are joined by parallel edges. A right prism has edges between the bases perpendicular to their planes. The optical use of a transparent prism is a separate application of this geometric shape.

For a homogeneous optical prism in the same medium on both sides, the minimum transmitted-ray deviation occurs for a symmetric path: the two internal refraction angles equal half its apex angle $A$. The expression requires $n\sin (A/2)\le 1$; equality is a grazing limiting path.

A prism with two hexagonal faces and six quadrilateral side faces. Its twelve vertices and eighteen edges provide an alternating aluminium–oxygen cage model when the graph is coloured bipartitely.