Dispersion and Spectra; Spectral Analysis
Why a glass prism splits white sunlight into a rainbow band — and how the resulting colours let us read the chemistry of a distant star.
Big Idea: The speed of light inside a transparent medium — and therefore its refractive index n — depends slightly on the light's colour (wavelength). This dependence is called dispersion. Because violet is slowed and bent more than red, a prism spreads white light into an ordered band of colours: a spectrum. Every chemical element emits and absorbs its own fixed set of wavelengths, so a spectrum is a fingerprint. Reading these fingerprints is spectral analysis, and it tells us what stars, flames and steel are made of without ever touching them.
By the end you will be able to:
- define dispersion and state that the refractive index depends on wavelength, n = n(λ);
- explain why violet is deviated most and red least, and order the visible spectrum;
- use n = c/v, λ = λ0/n and the thin-prism law δ = (n − 1)A;
- distinguish continuous, line-emission and line-absorption spectra and say what produces each;
- describe spectral analysis and list its uses in science and industry.