interference

In physics, the phenomenon of two or more wave motions interacting and combining to produce a resultant wave of larger or smaller amplitude (depending on whether the combining waves are in or out of phase with each other).

Interference of white light (multiwavelength) results in coloured bands; for example, the iridescent colours of oil films seen on water or soap bubbles (demonstrated by Newton's rings). Interference of sound waves of similar frequency produces the phenomenon of beats, often used by musicians when tuning an instrument. With monochromatic light (of a single wavelength), interference produces patterns of light and dark bands. This is the basis of holography, for example. Interferometry can also be applied to radio waves, and is a powerful tool in modern optical and radio astronomy.