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Interactive Lab

Prism Spectrometer

A beam of white light enters a triangular prism, refracts at both surfaces with wavelength-dependent bending via Cauchy’s equation, and fans out into a rainbow spectrum on a detector screen. Adjust the prism geometry and material to explore dispersion.

Refraction Data

n (400nm)--
n (550nm)--
n (700nm)--
Dispersion--

Geometry

Apex Angle60°
Incident Angle45°
MaterialCrown Glass
Deviation (550nm)—

Spectrum

Violet (380nm)
Blue (450nm)
Green (520nm)
Yellow (580nm)
Orange (620nm)
Red (700nm)
Adjust the prism apex angle and incident angle to see how dispersion changes. Different glass materials have different dispersive power — diamond separates colors the most due to its high refractive index. Toggle Ray Labels to see individual wavelength annotations.

The Physics of Dispersion

When white light enters a prism, it separates into a rainbow because the refractive index of glass depends on wavelength. Shorter wavelengths (violet) bend more than longer wavelengths (red). This phenomenon, called dispersion, was first systematically studied by Isaac Newton in 1666.

Cauchy’s Equation

n(λ) = A + B/λ² — The refractive index n varies with wavelength λ. The constants A and B depend on the glass material. Higher B means stronger dispersion.

Snell’s Law

At each prism face, n₁ sin(θ₁) = n₂ sin(θ₂) determines the refraction angle. The total deviation is δ = θ₁ + θ₄ − A where A is the prism apex angle.

Minimum Deviation

At minimum deviation, the ray path is symmetric inside the prism. This gives n = sin((A+D)/2) / sin(A/2).