# Understanding single slit interference

• XanziBar
In summary, the principle is that light waves bend at the boundaries of a slit, and this causes interference between waves that are diffracted.
XanziBar
I was just wondering if anyone was aware of a good explanation or physical cause of single slit interference that doesn't involve the Huygens-Fresnel principle. To me, the principle is not very intuitive, light does not eminate from other light (as far as I know). I think I understand that the wave bends at the boundaries of a single slit, but I do not understand what the diffracted wave interferes with.

It works just like water waves ... or sound waves. They all have different physical processes, but they all obey the wave equation.

The Huyghens' wavelets are a geometric "mechanism" for waves which explains the most common wave phenomena.

You say light does not emanate from other light, but that's a matter of interpretation. In the electromagnetic wave equation, a magnetic oscillation drives an electric oscillation which drives a magnetic oscillation. So, light at any point propagates to nearby points. Again, this is just an interpretation, since all we are sure about is the math, not the interpretation.

XanziBar said:
I was just wondering if anyone was aware of a good explanation or physical cause of single slit interference that doesn't involve the Huygens-Fresnel principle. To me, the principle is not very intuitive, light does not eminate from other light (as far as I know). I think I understand that the wave bends at the boundaries of a single slit, but I do not understand what the diffracted wave interferes with.

If you think of the word "interference" as applying to two or more ideal, point sources, this gives the simplest analysis of a wave situation in two dimensions (I.e. Young's slits). It's a special case of Diffraction and the Maths involves a straightforward Summation of finite elements (sources all over the Internet - to suit the individual reader). To get an idea of this subject, I think it is at least necessary to understand the Maths of two slit interference. Without the maths (geometry, at least) of the situation, I can't think of any way of understanding what's happening.

The word Diffraction applies to a real case where you can have extended sized sources. In that situation, you can treat the source as an infinite set of point sources and this involves Integration. A single slit diffraction pattern can be calculated by integrating the effect of contributions from elements across the slit width. You either need to accept it or learn about the integration process.

Whenever you see a real two slit pattern, what you are seeing is the result of two (broad) diffraction patterns, due to the individual slit widths, multiplied by the ideal (fine) interference pattern, due to the spaced sources. This is a very handy approach as it works perfectly in many cases and saves computation time and effort. (It's a Variable Separable problem)

## 1. What is single slit interference?

Single slit interference is an optical phenomenon that occurs when light passes through a narrow single slit and creates an interference pattern on a screen or detector. This pattern is characterized by alternating bright and dark bands, known as fringes, which are caused by the constructive and destructive interference of light waves.

## 2. How does single slit interference occur?

When light passes through a single slit, it diffracts, or spreads out, into a series of smaller waves. These waves then interfere with each other, creating the interference pattern on the screen. The central bright fringe corresponds to the direct beam of light passing through the center of the slit, while the dark fringes occur due to the cancellation of light waves from different parts of the slit.

## 3. What factors affect the interference pattern in single slit interference?

The interference pattern in single slit interference is affected by several factors, including the wavelength of light, the width of the slit, and the distance between the slit and the screen. A shorter wavelength of light results in a narrower interference pattern, while a wider slit or a larger distance between the slit and the screen will result in a wider pattern.

## 4. How is the intensity of light affected by single slit interference?

The intensity, or brightness, of the interference pattern in single slit interference varies along the fringes. The central bright fringe has the highest intensity, while the intensity decreases towards the outer fringes. The intensity also decreases as the wavelength of light increases or the width of the slit decreases.

## 5. What are the practical applications of single slit interference?

Single slit interference has many practical applications in fields such as optics, physics, and engineering. It is used in spectroscopy to analyze the properties of light, in interferometers to measure small distances and angles, and in diffraction gratings to separate light into its component wavelengths. It is also used in the design of optical instruments such as microscopes and telescopes.

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