Instead of shining monochromatic light (e.g. a laser) through a diffraction grating, what would happen if we shone a polychromatic light source (e.g. white light)? Do now:Wenerei, 29 Paenga-whāwhā 2015

Diffraction Gratings If we shine white light onto a grating, we produce a series of spectra each side of the central fringe This is because white light is made of many frequencies (colours) which all diffract at slightly different angles White n=0 violet red n=1 n=2 Diffraction Grating

Diffraction vs Refraction

The spectrum produced by a grating is more widely spread that that produced by a prism It is also the other way around (i.e. red is diffracted the most) – why? Red light has the longest wavelength, so is closest to the slit spacing, so diffracts the most Violet has the highest frequency, so interacts more when passing through a media, so slows down more (higher refractive index), so refracts more