This results in a pattern of concentric bright and dark rings, interference fringes. The geometry and the interference pattern Above: Here we use a sodium vapour lamp, in the box at left in this photo.
Since the gap between the glasses increases radially from the center, the interference fringes form concentric rings. For illumination from above, with a dark center, the radius of the Nth bright ring is given by r.
Hence, there is no path difference between the interfering waves. We analyse this geometry below. As a result, a dark area will be observed there.
There is a central dark spot around which there are concentric dark fringes. The additional path length is equal to twice the gap between the surfaces.
Now consider the phase difference due to reflections.
Phenomenon[ edit ] The phenomenon was first described by Robert Hooke in his book Micrographiaalthough its name derives from the physicist Isaac Newton, who was the first to analyze it.
A monochromatic source of light S is kept at the focus of a condensing lens L1. See Reflections and phases for an introduction.
When the air film is illuminated by monochromatic light normally, alternate bright and dark concentric circular rings are formed with dark spot at the centre. The thickness of the air film is almost zero at the point of contact O and gradually increases as one proceeds towards the periphery of the lens.
In white light, the rings are rainbow-colored, because the different wavelengths of each color interfere at different locations. You can also arrive at this conclusion from conservation of energy: The pattern is created by placing a very slightly convex curved glass on an optical flat glass.
The incident light is partially reflected from the upper surface of air film between lens and glass and light is partially refracted into the film which again reflects from lower surface with phase change of degree due to higher index of glass plate.
So, provided the coherence length is sufficiently long, these rays give constructive interference in reflection. One surface is slightly convex, creating the rings. These are similar to contour lines on maps, revealing differences in the thickness of the air gap.
Now consider a ring of radius r due to thickness t of air film as shown in the figure given below: The large dark patch at the centre is around the point where the convex lens surface touches the glass flat below it.
This leads to the alternating rings of constructive interference bright rings and destructive interference darkas shown in the photograph.
When a plano convex lens of long focal length is placed over an optically plane glass plate, a thin air film with varying thickness is enclosed between them.
The gap between the surfaces is constant along a fringe. The ray refracted in the air film is also reflected partly at the lower surface of the film. So the transmitted rays near the point of contact have constructive interference in transmission. The brightness of the reflected light depends on the difference in the path length of the two rays: This time we have destructive interference in reflection.
At right we see a photograph of the interference pattern.Newton's rings: Experiment, Theory An important application of interference in thin films is the formation of Newton's rings. When a plano convex lens of long focal length is placed over an optically plane glass plate, a thin air film with varying thickness is enclosed between them.
A convex lens is placed above a flat lens, which produces rings of light and dark fringes (bottom). Explanation In the traditional version of Newton's Rings, a slightly convex lens is placed above a flat glass plate or optical flat.
Newton's rings: Newton’s rings, in optics, a series of concentric light- and dark-coloured bands observed between two pieces of glass when one is convex and rests on its convex side on another piece having a flat surface. Thus, a layer of air exists between them. The phenomenon is.
Newton's rings is a phenomenon in which an interference pattern is created by the reflection of light between two surfaces—a spherical surface and an adjacent touching flat surface.
It is named for Isaac Newton, who first studied the effect in NEWTON’S RINGS PowerPoint Presentation, PPT - DocSlides- INTRODUCTION. The formation of Newton’s rings is an important application of interference of light wave from the opposite faces of a thin film of variable thickness.
Feb 27, · Newton's rings are formed due to interference between the light waves reflected from the top and bottom surfaces of the air film formed between the lens and glass sheet.
EXPLANATION The phenomenon of the formation of the Newton's rings can be explained on Status: Resolved.Download