Angular Dispersion — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Angular Dispersion Applicable for thin prisms where the prism angle A is very small (usually less than 10 degrees). Formula for deviation of a thin prism: delta = (n - 1)A Deviation for violet light: delta v = (n v - 1)A Deviation for red light: delta r = (n r - 1)A Angular dispersion theta is the difference between these deviations: theta = delta v - delta r Substitute and simplify: theta = (n v - 1)A - (n r - 1)A = (n v - n r)A Prism angle A must be small for the approximation sin(theta) approx theta to hold Valid for monochromatic limits of red and violet light in the visible spectrum Prism must be placed in air or the refractive indices must be relative to the surrounding medium Assuming angular dispersion is constant regardless of prism angle Confusing angular dispersion (theta) with dispersive power (omega), where omega = theta / delta mean Applying this formula to thick prisms with large apex angles