Diffraction
Diffraction, in physics, the spreading out of waves, such as those of water, sound, radio, or light, as they pass around an obstacle or go through an opening.
Water waves spread out as they move around an obstacle such as a projecting rock in a stream. These waves have been diffracted. Waves are also diffracted after flowing water has gone through some small opening.
Noise can be heard around the corner of a building because the sound waves have spread out and passed around the corner. If two rooms are connected by an open door, a sound from the far corner of one room can be heard in every part of the second room. The sound seems to come from the open door, because sound waves from the first room have been diffracted through the opening.
When radio waves strike an obstruction such as a mountain, some of the waves are reflected back toward the sending antenna. Others are spread out, or diffracted, and pass beyond the obstruction.
Light waves may be diffracted only under certain conditions. For example, light waves ordinarily will not turn corners, but they will be diffracted when they pass through tiny openings. When light strikes a diffraction gratinga small sheet of glass marked with thousands of parallel linesdiffraction causes the light waves to spread in such a way that they produce a spectrum, or rainbow. Scientists use diffraction gratings with or in place of prisms in spectroscopes, instruments that use spectra in the study of matter and its properties.