Newton's Rings

Introduction to Newton’s Rings

A Ring of Newton's is an Optical phenomenon that appears as a Ring of dark-colored lights or bands when one piece of glass is Convex and rests on another piece of flat glass. Therefore, there is space between them that is filled with air. Light waves are said to cause this phenomenon as their interference results in a brightening of light when their crests coincide, but the opposite occurs when the crest meets the trough. This is described as the destruction of light. During the transmission of light between the two pieces of glass, waves from both the top and bottom surfaces of the air film interfere with each other. This section will present all the information related to Newton's Ring. Newton was the first Physicist to investigate the Rings quantitatively, and he is credited with naming them after him.


What are Newton's Rings?

It is said that Newton's Rings are formed by the interference pattern between two surfaces caused by the light reflecting between them. There are two flat surfaces on either side of the sphere. In 1704, Isaac Newton described the effect in a treatise called Opticks based on his research. Newton's Rings are visible when viewed with monochromatic light as alternating bright and dark circles located at the point of contact between the two surfaces. The different wavelengths of light conflict at very different levels of thickness in the layer of air between the two surfaces when viewed in white light. This results in a pattern of a concentric circle of Rainbow colors.


An Optical glass that has a flat surface is placed on a very slightly curved Convex glass to create the pattern. At other points, there is a slight air gap between the two surfaces of the two pieces of glass which are in contact only at the center. The increasing distance between the center and the microscope is referred to as the radial distance. On the right side of one of the pieces, there is a small gap growing from left to right. In the monochromatic example, the source of color is a monochromatic single source of light shining through the top piece and refracting off the bottom and top surfaces. In the resulting superposition, the two rays are combined. 


This ray, however, generally travels a relatively long path as it reflects off the surface of the bottom. Two times the gap between the surfaces equals the additional path length.


A 180° phase reverse happens when the ray reflects off the bottom piece of glass. As a result, the phase reversal due to the internal reflection of the other ray from the underside of the top glass does not occur.


Formation of Newton’s Rings

Light waves are interfered with to create Newton's Rings when Reflections occur between the top and bottom surfaces of the air film formed between the lens and glass sheet.


According to the theory of waves of light, the formation of Rings of Newton's can be explained as follows:

  • In between the glass sheet and lens is an air film of varying thickness.

  • Reflection and refractive rays occur simultaneously when a ray strikes the lens surface.

  • Rays that are refracted have a phase change of 180 on the reflection when they strike a glass sheet.

  • If the path difference between two waves is m+1/2*1, an interference happens constructively, while destructively if the path difference between them is ml. This produces alternate bright and dark Rings.

FAQs (Frequently Asked Questions)

1. What are Newton's Rings and How They are Formed?

The rings of Newton's are formed as a result of interference which is between the light waves that are reflected from the top and bottom surfaces of the air film which is formed between the lens and glass sheet. A film of air which is of varying thickness is formed between the lens and the glass sheet.

2. Why Newton's Rings Circular?

The path of difference between the ray that is reflected and the ray which is the incident depends upon the thickness of the air gap between the lens and the base. As the lens is said to be symmetric along its axis the thickness is said to be constant along the circumference which is of a ring of a given radius. Hence we see that Newton's rings are circular.

3. Explain What the Newton Ring Experiment is.

The apparatus for Newton's ring and the aim of the experiment are to study the formation of Newton's rings in the air-film in between a lens which is a plano-convex and a glass plate by using a nearly monochromatic light from a sodium-source and hence this is to determine the radius of curvature of the plano-convex lens.


4. What are the Applications of Newton's Ring?

FRED generally is said to be allowed for simulation of physical optics phenomena such as diffraction and interference. With this capability, the components such as the Gaussian beam of laser and interferometers can be accurately modeled and incorporated into a system that is optical.


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5. How did Newton's Rings get its dark central fringe?

Newton's Rings are formed by interference between thin films of uniformly increasing thickness on either side of a bright or dark central circle. A film of air is present between the lens and the glass, but there is reflection coming from the denser medium at the lower surface of the film. As a result, the path difference is λ/2. Therefore, the center of the image has a dark fringe.

6. Why Newton's Rings lit by Monochromatic light?

When monochromatic light is used there is no doubt about the interference pattern. Because different wavelengths of light interfere at different thicknesses, white light will not produce a clear interference pattern.

7. In Newton's Ring, what is a backlash error?

Play in the screw increases with use or as a result of wear and tear, such that when it is rotated in a particular direction the screw slips into the nut and no linear distance is covered for certain rotations of the screw head. The error that results from this is known as a backlash error.

4. Why are Newton's Rings circular?

Depending on the thickness of the air gap between the lens and the base, the path of difference between the ray that is reflected and the ray which is incident is different. A symmetrical lens will have the same thickness across its axis as it will have along its circumference, as if it were a Ring of given radius. As a consequence, Newton's Rings are Elliptical.

9. Can you explain why the center of Newton's Rings is perfectly black?

Because of the thin air film formed between the glass plate and lens at the center, the central fRinge of Newton's Rings is dark in the reflector system. As a result, the angle of incidence between the incident and reflected rays is equal to zero at the geometrical path.

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