Diffraction grating
Intermediate
Many slits give sharp spectra.
d sinθ = mλMany equally spaced slits give sharp maxima at d sinθ = mλ. More lines produce narrower and brighter peaks; used in spectrometers.
600 lines/mm, λ = 500 nm: first order at 17.5°.
Different from the single slit pattern.
In more detail
A diffraction grating has many closely spaced slits and produces sharp maxima at angles given by d sin θ = mλ. It separates colours more sharply than a prism.
Real-world uses
- Spectrometers use gratings to analyse light from stars and chemicals.
- CD and DVD surfaces act as gratings, producing rainbow colours.
- Spectrometers use gratings to split light into sharp spectral lines for identifying elements in stars.
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Frequently asked questions
What is the grating equation?
d sin θ = mλ, where d is the spacing, θ the angle and m the order.
Why are gratings better than prisms?
They spread light more uniformly and the separation does not depend on refractive index.
Why are gratings better than prisms for spectra?
Gratings give sharper lines and a more even spread of colours, which makes spectral measurement more precise.
Related topics in Optics
Newton's rings · Michelson interferometer · Single slit diffraction · Resolving power · Polarisation of light · Malus's law