Newton's Rings, a pattern of light and dark circles visible when a convex lens is placed, curved side down, on top of a flat piece of glass. The pattern was first observed by Sir Isaac Newton. The rings are caused by interference of light waves.
When a beam of light is directed downward onto the two pieces of glass, two overlapping beams of light are formed—one from light reflected by the lower surface of the curved glass and the other from light reflected by the upper surface of the flat glass. The light reflected from the flat glass travels farther than the light reflected from the curved glass. Depending on the distance between the two surfaces, light waves in the two beams may be in phase, reinforcing each other, or they may be out of phase, canceling each other out. Because the distances between the two reflecting surfaces increases with distance from the point where the lens and flat glass make contact, the areas where the waves are in phase and out of phase occur in concentric bands around the center of the lens.
If the beam of light directed at the two pieces of glass is monochromatic (of a single wavelength), the rings are thin circles of a single color. If white light (which consists of light of many different wavelengths) is used, the rings are fewer in number, but highly colored.