• $summary_{type}$: concept
• $word_{count}$: 170

A prism of angle A causes deviation δ = $i_{1}$ + $i_{2}$ - A, with the constraint $r_{1}$ + $r_{2}$ = A inside the prism. Minimum deviation occurs when $i_{1}$ = $i_{2}$ (symmetric passage), giving the important formula n = sin$\frac{(A + δ_m}{2}$)/sin$\frac{A}{2}$. For thin prisms (small A), the deviation simplifies to δ = (n-1)A, which is independent of the angle of incidence. The deviation versus incidence (δ-i) curve is U-shaped with a single minimum at δ_m. For each δ > δ_m, there are two possible angles of incidence. The condition for a ray to emerge from the second surface is A < 2θ_c (where θ_c is the critical angle). If A exceeds 2θ_c, total internal reflection occurs at the second face. JEE frequently tests minimum deviation calculations, typically requiring students to find the refractive index or the angle of incidence at minimum deviation.