Theory

• •A light ray bends twice in a prism — once at each surface.
• •Total deviation δ depends on: angle of incidence i, prism angle A, refractive index μ.
• •Geometric relation: δ = i₁ + i₂ − A and r₁ + r₂ = A.

Exam tip: When δ is minimum, the ray inside the prism is parallel to the base, i₁ = i₂ and r₁ = r₂.