A monochromatic green light of wavelength 520 nm passes through a triangular prism with apex angle 30°. The refractive index of the prism for this green light is 1.52. Assuming small angles, calculate: (i) the deviation of the emergent ray from the incident ray in degrees; (ii) the angular dispersion between green (520 nm) and violet (400 nm) rays, where the refractive index for violet light is 1.55.

Step-by-step solution

1. 1. For small angles, the total deviation $\delta$ of a prism is approximately $\delta \approx (n-1)A$, where $n$ is the refractive index and $A$ the apex angle.
2. 2. For green light: ${\delta }_g\approx (1.52-1)\times 30°=0.52\times 30°=15.6°$.
3. 3. For violet light: ${\delta }_v\approx (1.55-1)\times 30°=0.55\times 30°=16.5°$.
4. 4. Angular dispersion is $\Delta \delta ={\delta }_v-{\delta }_g=16.5°-15.6°=0.9°$.
5. 5. Thus, (i) 15.6° deviation for green; (ii) 0.9° dispersion between green and violet.

Concept tested: Prism deviation and dispersion

Published 13 October 2026 · How this solution was prepared and checked