Newton’s rings occur when a convex lens is in contact with a flat glass, creating concentric circles due to interference between reflected light waves. The phenomenon can be used to determine the quality of a lens. Newton observed the rings in 1675 and believed they supported his particle theory of light, although they are now understood to be caused by light waves. The rings are thicker closer to the center due to the curvature of the lens.
The term “Newton’s rings” refers to a phenomenon that occurs when a curved piece of glass, typically a convex lens, is brought into contact with a flat piece of glass. The curved glass rests on the flat glass, creating an ever-widening veil of air between them along the length of the curve. When white light is directed into the curved glass, a series of concentric circles appear, like a bull’s eye. 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 Newton’s rings are typically dark alternating with bright, with the dark beginning in the center. The phenomenon occurs due to interference between the light reflected from the two surfaces. In practical application, Newton’s rings can be used by lens manufacturers to determine the quality of a lens. In a well-made lens, the rings should be even.
In the center of the rings, the largest ring, forming a complete circle, is dark. The remaining rings alternate between dark and light due to the nature of the interference that creates them. The light waves reflected by 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 cancel each other out. Constructive interference occurs when the high or low points of light waves align with each other.
Another characteristic of Newton’s ring phenomenon is that circles closer to the center are thicker than those at the periphery of the circle. This has to do with the curvature of the convex lens. As the lens moves away from the underlying flat glass, the rings get 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 experiment with Newton’s rings used glass that created a wedge-shaped gap, but later versions of the experiment used a convex lens. Modern instruments created to demonstrate the phenomenon also use a convex lens.
Although modern scientists believe that Newton’s rings are caused by light waves, Newton himself saw the phenomenon to support his theory that light consisted of particles. Some of his discoveries and observations, however, required him to use theories in line with wave theory. The observation of Newton’s rings is just one of many scientific theories made by Newton; in fact, many believe he made a greater contribution to scientific knowledge than anyone else in history.
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