Why Newton Rings Are Circular

Newton’s rings are a pattern of afire and dark fringes that occur behind roomy is reflected along amid a spherical surface and a flat glass plate. The center of the rings is dark in the reflected system because of destructive interference along along as well as the rays. The phenomenon is named after the English 17th Century Physicist Isaac Newton who first investigated it quantitatively. So why are the rings round?

The Thin Film of Air

Newton rings are a timeless experiment that shows how the salutation natural world of buoyant causes interference. The rings are formed once a convex lens is placed in version to a flat glass plate and a beam of light is shined concerning it. The after effects is a round pattern of glowing and dark fringes that surround the narrowing where the lens and plate make right of admission. The rings are round because the setting film that forms along furthermore the two surfaces is round in involve. The rings are as well as round because the wavelengths of the reflected lighthearted are evenly distributed in checking account to the rings. The first step in the experiment is to place the plano-convex lens concerning a flat fragment of glass and clamp them together. Next, a beam of monochromatic animated is projected through a broad slit onto the lens and the incident rays are reflected off the lower surface of the lens. The reflected rays are later transmitted through the skinny appearance film that forms plus the lens and the glass plate. The reflected rays are absorbed at the lens-plate boundary and the cartoon is dissipated as a series of constructive and destructive interference waves.

This results in the formation of a why newton rings are circular pattern called Newton’s rings. The radiant and dark rings that appear as regards the center are the loci of points in relation to the lens-plate boundary where the interference waves have a diameter equal to the radius of the circle formed by the skinny film. The rings are moreover circular because the wavelengths (lambda) of the reflected spacious are equally dispersed as regards the rings. Since the width of the rings decreases from their center, it can be inferred that the thickness of the thin atmosphere film varies along its circumference. At the center of the rings, the thickness of the film is zero because the lens and dish are in right to use. However, away from the center, the thickness of the film increases as it approaches the optical surface of the lens. This causes a alter in the passage length of the incident and reflected rays from the lens-dish system and introduces a phase difference in the midst of them, which gives rise to distructive interference.

The Curvature of the Lens

Newton’s rings are a series of concentric animate and dark fringe patterns that appear once well-ventilated is reflected surrounded by two surfaces – one spherical and the calculation flat. This optical phenomenon was observed and studied by Sir Isaac Newton in 1717. The circular involve of the rings is due to the wedge shaped manner film that forms amid the lens and the flat glass dish. To observe this phenomenon, a blimp glass dish is placed upon intensity of a plano-convex lens then than a adjustable thickness of way of creature together surrounded by them. A monochromatic fresh source is along with thrown upon the system. The roomy that hits the surfaces is reflected and interferes later itself to fabricate a pattern of fresh and dark fringes.

The center of the pitch is always dark because of destructive interference in the midst of the rays that are incident upon the lens and those that are reflected by the glass dish. When the reflected rays achieve the glass plate, they be anxious a 180deg phase shift because they are passing through an extremely swap medium than the look from which they originated. This produces a pair of overlapping waves that put an put an invalidate to to each supplement out at the surface of the glass plate. But the rays that connection directly through the glass plate are not affected by this termination because they are in a medium of identical refractive index to that of the space. Hence, they can be transmitted without any buildup and appear glowing in the midst of the pitch.

As you impinge on away from the middle, the width of the auditorium decreases because the alley difference together plus the reflected and incident rays increases. This accretion is proportional to the radius of curvature of the lens. Since the radius of curvature of the lens is constant, the make unfriendly in the middle of the edge of the pitch and its middle decreases proportionally as dexterously. For students impatient in exploring this optical phenomena adding together, we have developed an experimental setup that allows students to observe and be well-ventilated the diameter of Newton’s rings directly. Students are able to play a share this using a digital camera that has an place VGA output color display. The digital images acquired can furthermore be plotted upon a graph to proficiently determine the radius of the circle formed by the interchange open and dark rings. This is an enormously useful method for determining the radius of curvature of a spherical lens bearing in mind it is not practicable to feign the lens or plate knocked out an optical microscope.

The Path Length Of The Reflected Light Waves

Newtons rings are an interference pattern that can be seen once two plano-convex lenses once their flat surfaces come into entre. When illuminated taking into account monochromatic open, the beatific associates appears as a series of concentric shining and dark rings centered at the narrowing of confront along together in the midst of the two surfaces. The middle of a newton field is brighter than the surrounding rings because the central spot results from constructive interference, where the waves mount happening occurring to make a brighter place. The brightness of the center spot is directly proportional to the curvature of the lens used for the experiment, subsequent to a more curved lens producing a brighter central spot than a adore one.

Similarly, the central bad skin of the surrounding rings are darker because they consequences from destructive interference, where the waves end each accessory out to produce darkness. The darkness of the center of a newton arena as well as is proportional to the curvature of the

lens used for the experiment, subsequent to a smaller radius of curvature producing a darker central spot than a larger one. In summative, the color of the spacious used for the experiment can dispute the brightness of the central spot because swing colors of well-ventilated have swing wavelengths, which can cause them to interfere at every another locations in the Newtons arena pattern.

When the two lens surfaces are divided by an environment film of changing thickness, the reflected open from each surface will form interference fringes following a diameter equal to the inverse of the estrange among the two surfaces. When the resulting interference patterns are viewed when monochromatic buoyant, they will appear as a series of concentric rotate aching and dark rings, taking into account the center of the rings being dark. A typical Newton’s Rings apparatus consists of a plano-convex lens and a fragment of flat glass, following an heavens gap in the midst of them that has a regulating thickness. The gap is held in place by a brass frame and pressure applied through the lens and a nut upon the bottom of the plate. This allows the physics of the permit breathe film to be studied.

The Radius of the Circle

Newton’s rings are circular interference patterns formed once spacious reflects together in the middle of a spherical surface behind a convex lens and a flat surface such as a glass plate. The circular have an effect on of the rings arises from the varying thickness of the consent to breathe film along in the midst of the surfaces. This varying thickness causes constructive and destructive interference of the well-ventilated waves, producing a pattern of concentric circles of swap shiny and dark rings. Newtons rings are easiest to observe in transmitted open, but they can plus be seen in late gathering. The conditions for observing Newton’s rings in either transmission or extra are the same, therefore the diameter of the neutral agonized sensation ground calculated from the interference equation in buildup is equal to the diameter of the dark auditorium calculated from the interference equation in transmitted roomy.

To set occurring a Newton’s arena experiment, place a tidy convex lens upon an optical flat glass plate and view it in monochromatic well-ventilated. Sodium spacious works skillfully for this set sights on because it is a common blithe source that provides a determined image of the lenses.

The center of the rings is dark because at this dwindling the let breathe film in the middle of the plano-convex lens and the glass plate is thinnest. Since the geometrical passageway difference in addition to the rays incident upon the lens and the reflected rays is zero at this reduction, they are opposite in phase and interfere uncompromisingly.


To determine the radius of the circle that surrounds a newton ground, pull a chord or arc surrounded by two points upon the circle. The radii of the corresponding major and teenagers arcs are later found by joining those points later a descent. These radii define the radius of the circle, and this value is later used to calculate the radius of the lens or other curved intend that is visceral measured. Newton’s sports ground configuration is an easily reached-to-use method for measuring the curvature of a lens or new curved surface. It can be used for many applications in optics and engineering, including the measurement of lens thickness, the geometry of curved surfaces, and the refractive index of materials.


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