[Physics Class Notes] on Newton's Rings Pdf for Exam

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.