Newton's Rings Experiment: A Detailed Explanation of the Optical Phenomenon
Newton's Ring Experiment is an optical phenomenon where a series of concentric bright and dark rings appear due to light interference between two surfaces—a convex lens and a flat glass plate. First investigated by Sir Isaac Newton in 1666, the phenomenon highlights the wave nature of light. Monochromatic light creates distinct alternating rings, while white light produces a rainbow-coloured pattern due to varying wavelengths interfering at different air gap thicknesses. On this page, you will learn about the History and Discovery of Newton's Rings, Theory and Formation of Newton's Rings and more.
History and Discovery of Newton's Rings
The phenomenon was initially described by Robert Hooke in 1665 in Micrographia. Isaac Newton, while studying light during the Great Plague in 1666, quantitatively analysed this effect and documented it in his treatise Opticks (1704). The rings are named in Newton's honour, though his interpretation of the phenomenon differed from modern wave theory.
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 colour 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.
Newton's Ring Experiment Theory
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.
Key Concepts:
Air Film Thickness: The air gap increases radially from the centre, influencing interference.
Path Difference: Constructive interference occurs when the path difference equals an odd multiple of λ/2, while destructive interference happens at even multiples.
Phase Reversal: Reflection at the air-to-glass boundary causes a 180° phase shift.
Interference Patterns in Newton's Rings
Bright Rings:
Formed at points where the path difference between reflected rays equals $ \lambda/2$, resulting in constructive interference.Dark Rings:
Formed where the path difference equals 2nλ/2, resulting in destructive interference.Concentric Circles:
The varying air gap creates concentric fringes. In non-axially symmetric setups, the patterns take other shapes.
Quantitative Relationships in Newton's Rings
Radius of Bright Rings:
For monochromatic light with a dark center:
$r_N = \sqrt{\lambda R \left(N - \dfrac{1}{2}\right)}$
Where:$r_N$: Radius of the Nth bright ring
λ: Wavelength of light
R: Radius of curvature of the lens
N: Ring number
Air Gap Calculation:
The air gap (t) between the surfaces for a given radius (r) is:
$t = \dfrac{r^2}{2R}$.
Steps to Perform Newton's Ring Experiment Calculation
Measure Radii of Rings:
Use a travelling microscope to measure the diameters of several bright or dark rings. Half these values to get the radii.Determine the Difference Between Consecutive Rings:
Calculate the difference in the square of the radii of consecutive rings ($r_{N+1}^2 - r_N^2$).Apply Formulas for Desired Values:
Use the above formulas to calculate the wavelength of light (λ) or the air film thickness (t).
If the radius of curvature (R) is unknown, it can be determined using other experimental data.
Application of Newton's Ring
Measuring Wavelengths:
Newton's Rings provide a precise method to measure the wavelength of monochromatic light.Determining Lens Curvature:
The radius of curvature of a lens can be calculated using the ring pattern.Testing Surface Flatness:
The technique is used to detect surface irregularities as small as a fraction of the wavelength of light.Research in Optics:
It aids in studying interference, wave behaviour, and light reflection principles.
FAQs on What Is Newton's Ring? A Complete Explanation
1. What is Newton's Ring in Physics 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 Rings are 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 Newton's Ring In Physics 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.
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.
8. 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 centre 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.
10. What causes the alternating bright and dark rings in Newton's Rings?
The alternating bright and dark rings are caused by constructive and destructive interference. When the path difference between the light waves is an odd multiple of half the wavelength, constructive interference occurs, resulting in a bright ring. Destructive interference happens at even multiples, forming dark rings.
11. What is the purpose of Newton's Ring experiment?
The Newton's Ring experiment is conducted to study the interference pattern in thin films and to determine parameters such as the wavelength of light, the radius of curvature of lenses, and the flatness of surfaces.
12. How does the radius of the ring depend on the wavelength in Newton's Rings?
The radius of each ring is proportional to the square root of the product of the radius of curvature of the lens and the wavelength of light. Longer wavelengths produce wider ring patterns.
13. Why is white light not suitable for Newton's Rings experiments?
White light contains multiple wavelengths that interfere at different thicknesses of the air gap, resulting in overlapping patterns. This creates a rainbow-like effect instead of distinct interference fringes, making it unsuitable for precise analysis.
