LAB GUIDE / PHOTONICSWhy does a prism split light?
Refraction occurs when light crosses a boundary between different refractive indices. Snell's law is n₁ sin(θ₁) = n₂ sin(θ₂). In a dispersive medium, the index also changes with wavelength, so colours bend by different amounts.
The laboratory uses ray intersection with a triangular prism. Its Sellmeier equation estimates n(λ) for N-BK7 glass, fused silica and the ordinary ray of sapphire. Rays are traced through entrance, potential internal reflection and exit faces.
Try white light at 0°, turn the prism by 10°, then compare BK7 with silica. Under some angles the ray may miss the prism or undergo internal reflection; these are valid outcomes.