• Tags: prism, deviation, dispersion
• Difficulty: Moderate

A prism of angle A causes deviation δ = $i_{1}$ + $i_{2}$ - A (by geometry of the prism).

At minimum deviation: $i_{1}$ = $i_{2}$ = i, $r_{1}$ = $r_{2}$ = A/2, and the ray passes symmetrically through the prism. The refractive index: n = sin$\frac{(A + δ_m}{2}$) / sin$\frac{A}{2}$.

For a thin prism (small A): δ = (n-1)A, independent of angle of incidence. This is widely used in JEE problems.

Angular dispersion = δ_V - δ_R = ($n_V$ - $n_R$)A. Dispersive power ω = $\frac{n_V - n_R}{(n_Y - 1)}$.