History And Formation Of Newtons Rings

History And governing body Of due norths RingsIn this experiment the physical property of interruptnce of cast down will be use to determine the wavelength,, of a light source. The hurly burly fringe system here is a pattern of concentric circles, the diameter of which you will measure with a locomotion microscope (which has a Vernier scale). If a clean convex lens is placed on a clean trash slide (optically flat) and viewed in monochromatic light, a series of sound may be seen around the point of contact between the lens and the slide. These rings atomic number 18 known as Newtons rings and they sneak from the birth control device of light reflected from the glass surfaces at the glory motion-picture show between the lens and the slide. The data-based set-up is shown in figure 1.History of history of Newtons ringThe phenomenon of Newtons rings, named aft(prenominal) sir Isaac Newton who first studied them in 1717, Newtons rings is a pattern of interference caused by two surfaces after reflection of light a expanse surface and an adjacent flat surface. When view with monochromatic light its appears as a series of concentric, alternating bright and dark rings cente going at the point of contact between the two surfaces. When we see with white light, it forms like a rainbow colours concentric ring pattern because the different wavelengths of light interfere at different thickness of the layer between the surfaces. The light reflected from both surfaces caused by constructive interference, while the dark rings atomic number 18 caused by destructive. Perhaps, the eruptside rings are more closely spaced than the inner.So the above phenomenon was first described by Robert Hooke in his 1664 book Micrographia although its name derives from the physicist sir Isaac Newton, who was the first to see it.Newtons ringsThe term Newtons rings is a ring make by the glass of veer, typically a convex lens, is put in contact with a glass of a plan surface. The curved glass kept on the plan glass, forming a film of way between them is increasingly larger on the length of the curve. When light is directed into the curved glass, a many of concentric circles appears. That is why the rings are referred to as Newtons rings. Which was the first to observe the phenomenon by Sir Isaac Newton?The Newtons rings formed will be phenomenon typically is dark alternating with bright, with the dark beginning in the center. It is formed as a result of interference between the light reflected by the two surfaces. Towards the application, Newtons rings can be used by lens makers to find out the quality of a lens. In a well-made lens, the rings should be uniform.When a convex surface with its Plano-convex lens is placed on a glass sheet, an air film of in stages increasing thickness outward is formed between the lens and the sheet. The thickness of film at the point of contact is zero. If light is allowed to fall on the lens, and the film is viewed in refl ected light, alternate bright and dark concentric rings are seen around the point of contact.(Source google.com)Newtons Rings, it is visible a pattern of light and dark circles 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 light is falls downward onto the two pieces of glass, two overlapping beams of light are formed-one from light reflected by the reduce surface of the curved glass and the other from light reflected by the upper surface of the flat glass. The light reflected from the canvas glass moves farther than the light reflected from the curved glass. It depends on the distance between the two surfaces, light waves in the two beams may be in level, and reinforcing each other or they may be out of phase, canceling each other out. Since the distances between the two reflecting surfaces increases with distance from the point where t he 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 falls at the two pieces of glass is of a single wavelength i.e. monochromatic, the rings are thin circles of a single color. The rings are fewer in number, but highly colored when white light is usedFormation of Newtons RingsNewtons rings are formed as a result of interference between the light waves reflected from the top and bottom surfaces of the air film formed between the lens and glass sheet.The phenomenon of the formation of Newtons ring can be explained on the basis of wave theory of light i.e.An air film of varying thickness is formed between lens and the glass sheet.When a ray is incident on the surface of the lens, it is reflected as well as refracted.When the refracted ray strikes the glass sheet, it undergoes a phase change of 180 on the reflection.Interference occurs between two waves which interfere c onstructively if track differences between them is (m+1/2) 1 and destructively if path difference between them is ml producing alternate bright and dark rings.Radius of Newtons RingLet the radius of curvature of the convex lens is R and the radius of ring is r. Consider light of wave length l falls on the lens. After refraction and reflection two rays 1 and 2 are obtained. These rays interfere each other producing alternate bright and dark rings. At the point of contact the thickness of air film is zero and the path difference is also zero and as a 180O path difference occurs, so they cancel each other and a dark ring is obtained at the centre.As we move away from the central point, path difference is also changed and alternate dark and bright rings are obtained. Let us hypothecate that the thickness of air film ist.By using the theorem of geometry,x = xr x r = t (2R t)= (2Rt -)Sincet is very small as analyze to r, therefore neglecting = 2Rt r2 = 2Rt.. (1)In thin films, path diff erence for constructive interference is 2nt = (m+1/2) l Where n= refractive indexfor air n = 1Therefore, 2t = (m+1/2)l .. (2)For first bright ring m = 0for second bright ring m = 1For third bright ring m = 2SimilarlyFor Nth bright ring m = N-1 Putting the value of m in equation (2) 2t = (N-1+1/2)l2t = (N-1/2)l t =1/2 (N-1/2) l .. (3)Putting the value oft in equation (1)r2 = 2Rtr2 = 2R. 1/2 (N-1/2) lr2 = R (N-1/2) l=Where N is the bright ring number, R is the radius of curvature of the lens the light is passing through, and is the wavelength of the light passing through the glass.Working of Newtons RingWhen convex surface of a long central length lens is placed in contact with a plane glass phonograph recording and clamped together, as shown in cross section below. Adjustment screws are tightened to secure intimate contact at the center.Between the two surfaces of glass a thin film of air is formed and when this band is viewed under reflected light from an extensive light source . We ignore reflections from the top (Plano-convex lens) and bottom (plane glass disk) as these reflections just contribute to the overall glare. Since the wave is going from a higher to degrade refractive index medium, there is no phase change at the glass air surface of convex lens. Whereas at the air-glass surface of the plane disk suffers a half-cycle phase shift due to reflection.Let R be the radius of curvature of the convex lens, r distance from center and the t air film thickness.Then, = 2RtAnd the radius of the bright ring is given by= (N + ) R Here the two glass surfaces are in close contact and there is no reflection because it is as if there were no surfaces. The reflected light is almost white in colour for first maximum, this is because the distance between the two glass surfaces is much(prenominal) that its almost () for the entire spectrum. Similarly succeeding rings exhibit more and more colour. Where the thickness is odd number N of (1/4) for green, and where b lue is about (N+1) (1/4) and red is (N-1) (1/4) will be most monochromatic ring. Therefore blue and red at reflection minima while green is at a reflection maximum.The experimental procedure to find the radius of Newtons bright ring is as follows.The convex surface of large radius of curvature is placed in contact with a plane glass disk and clamped togetherAdjustment screws are tightened to secure intimate contact at the centerA thin film of air is formed between the 2 surfaces of glassThe thin film of air is viewed under reflected light from an extensive light sourceReflections from the top ( Plano-convex lens) and the bottom ( plane glass disk) are ignored, since these reflections just contribute to the overall glareThe reflections of interest involves where the surfaces in contactSince the wave is going from higher to a lower refractive index medium, there is no phase change at the glass-air surface of the convex lensWhereas at the air-glass surface of the plane disk suffers a half-cycle phase shift due to reflection.Taking R as the radius of curvature of the convex lens, the relation between the radius of the ring r and the air-film thickness t is given by r2 = 2Rt .Then radius of the nth bright ring will be given by =The Newtons ring is used to Illustrate the interference fringes formed in the air film between optical surfaces. Newtons rings are used to determine the radius of curvature of the bi convex or Plano-convex lens Measure the refractive index of a substance placed beneath the same lens. Determine the wavelength of sodium light