# Order of Dark Fringes: Understanding Interference Patterns

• M. next
In summary, the conversation discusses the order of dark fringes in an experiment involving a lens in contact. It is suggested to use an equation for the difference between two adjacent rings rather than measuring the individual rings. It is also recommended to measure the diameter of the rings as the center may be difficult to determine. Additionally, the slope of the graph can be used to calculate the wavelength.
M. next
After that, please point out, the order of the dark fringes. I mean I can't see where is m=0 dark fringe? Where to start?
I want to know so I can know that radius enclosed by each fringe.
Thanks.

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If the lens is in contact then the center is "ring" zero, but it's very wide.

It's been many years but if I remember correctly... You probably have an equation for the radius of the ring, however when doing the experiment it might be best to write an equation for the difference between two adjacent rings. Then you don't need to know which is ring zero or even measure it. Your equation will have a term something like (n+1) -n which equals 1 so the ring number dissapears.

If you plot a graph and it doesn't pass through the origin either you started counting from the wrong place or the lens wasn't really in contact. Either way the slope of the graph wouldn't change and can be used to calculate the wavelength.

I'd also measure the diameter of the rings rather than the radius because it's hard to know where the centre is exactly. The rings have thickness so you have to measure from the middle of the line to mddle of line.

## 1. What is the Order of Dark Fringes in interference patterns?

The Order of Dark Fringes in interference patterns refers to the number of dark fringes observed in a diffraction pattern. These dark fringes occur when two or more waves interfere with each other and cancel out, resulting in a dark spot on the screen or surface where the pattern is observed.

## 2. How is the Order of Dark Fringes related to the wavelength of light?

The Order of Dark Fringes is directly related to the wavelength of light. As the wavelength of light increases, the distance between fringes also increases, resulting in a higher order of dark fringes. This relationship is described by the equation mλ = dsinθ, where m is the order of the fringe, λ is the wavelength of light, d is the distance between the source and the screen, and θ is the angle of diffraction.

## 3. What factors affect the Order of Dark Fringes?

The Order of Dark Fringes is affected by several factors, including the wavelength of light, the distance between the source and the screen, and the angle of diffraction. Additionally, the medium through which the light travels can also influence the Order of Dark Fringes, as well as any obstructions or obstacles in the path of the light waves.

## 4. How can the Order of Dark Fringes be used to determine the wavelength of light?

By measuring the distance between fringes and knowing the distance between the source and the screen, the Order of Dark Fringes can be used to calculate the wavelength of light using the equation mλ = dsinθ. This is a common technique used in experiments and demonstrations to determine the properties of light.

## 5. What is the significance of understanding the Order of Dark Fringes in interference patterns?

Understanding the Order of Dark Fringes is crucial in studying the properties of light, as it provides valuable information about the wavelength of light and how it interacts with different mediums. Additionally, interference patterns have many practical applications, such as in diffraction gratings used in spectrometers and in the production of holograms.

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