BRAINCAKEUsing Diffraction Gratings to Analyse Starlight
A diffraction grating is a slide with many equally spaced parallel slits (lines), often hundreds per millimetre. Light passing through the slits diffracts, and the waves from the slits interfere. Bright maxima (orders) are produced in directions where the waves from neighbouring slits arrive in phase, which happens when the path difference is a whole number of wavelengths:
where d is the grating spacing (distance between adjacent slits), θ is the angle of the nth order maximum from the straight-through (zero order) direction, n is the order number and λ is the wavelength. If a grating has N lines per metre, d = 1/N.
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