What are Newton's Rings?

The term "Newton's rings" refers to a phenomenon that occurs when a curved piece of glass, typically a convex lens, is put in contact with a flat piece of glass. The curved glass sits on the flat glass, creating a film of air between them is increasingly larger along the length of the curve. When white light is directed into the curved glass, a series of concentric circles, like a bull's eye, appears. Sir Isaac Newton was the first to observe the phenomenon, which is why the concentric rings are referred to as Newton's rings.

The concentric circles produced by the Newton's rings phenomenon typically are dark alternating with bright, with the dark beginning in the center. The phenomenon occurs as a result of interference between the light reflected by the two surfaces. In practical application, Newton's rings can be used by lens makers to determine the quality of a lens. In a well-made lens, the rings should be uniform.

In the center of the rings, the largest ring, which forms a full circle, is dark. Remaining rings alternate between dark and light because of the nature of the interference that creates them. Light waves reflected from the two pieces of glass cause both destructive and constructive interference. In destructive interference, the high point of one wave meets the low point of the other, and they effectively cancel out each other. Constructive interference occurs when the high or low points of the light waves align with each other.

Another characteristic of the Newton's ring phenomenon is that the circles nearer the center are thicker than those on the periphery of the circle. This has to do with the curvature of the convex lens. As the lens becomes more distant from the flat glass beneath it, the rings become thinner and closer together.

Sir Isaac Newton first discussed the observation of these rings in 1675. He also described the phenomenon in his 1705 book "Optics." Originally, his Newton's rings experiment used glass that created a wedge-shaped space, but later versions of the experiment used a convex lens. Modern instruments created to demonstrate the phenomenon also use a convex lens.

Though modern scientists believe that Newton's rings are caused by light waves, Newton himself saw the phenomenon as supporting his theory that light consisted of particles. Some of his discoveries and observations, however, required him to use theories that aligned with wave theory. Observing Newton's rings is only one of the many scientific theories Newton made; in fact, many believe that he made a larger contribution to scientific knowledge than anyone else in history.