Interactions of Light with Solutions and Suspensions - Spectral Changes

A diffraction grating can be used to study how light that has passed through a colloidal suspension or solution is altered.

Discussion

The transmission diffraction grating we use for these demonstrations is a sheet of transparent material with thousands of evenly spaced, parallel scratches etched on its surface. It has 75,000 of these scratches, each of which acts like a single slit through which light passes, but which collectively produce a diffraction pattern that is brighter (more slits = more light passing through) and that has successive bright and dark regions much more widely separated. This diffraction grating, framed between two pieces of glass and placed in front of the screen, displays the spectrum of the light reflected by the screen.

At the beginning of this movie, we can see three images produced by the grating: the central image (called the zeroth-order diffraction pattern), and images to the right and left of the central image (called the first-order diffraction patterns). When the diffraction grating is removed, we can see the undiffracted reflection of the beam of light from the overhead projector.