© Eli Sidman, Technical Services Group, MIT.
This photograph of a ripple tank shows the interference pattern produced by a plane wave passing through a slit. Waves that pass through a narrow slit tend to spread, or diffract. The slit here is about two wavelengths wide, and the waves move in arcs that clearly fade out at large angles. The pattern is called single-slit diffraction, and if the slit is made even narrower the diffraction pattern shows not only a maximum in the center, but also side lobes. The diffraction of light waves can be observed by making a very narrow slit and illuminating it with a laser pointer. It helps if the room is dark. (Unit: 5)