Young's Double Slits: Coherent Light Explained

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In summary, the purpose of a single slit is to ensure that the light passing through the double slits is coherent, meaning it has the same wavelength and frequency and is in phase. This is important for producing a pattern with symmetry. A standard light bulb emits light of various wavelengths and frequencies, resulting in destructive interference and a lack of coherence. However, collimating the light source can increase the coherence length. The single slit does not change the wavelength or frequency of the light, but rather ensures that the light passing through is coherent with itself, resulting in a coherent pattern.
  • #1
kkmans
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I would like to ask why a single slit is needed.
I have done some research and find that it makes sure the light goes to the double slits is coherent.

How can a single slits produce coherent light ?
and why the light comes from a natural source (e.g. lamp) is not coherent ?
In my knowledge, light is conherent within the coherent length..

thank you.
 
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  • #2
Coherent light means light of same wavelength and frequency, also it has to be in phase

A standard bulb emits light of lots of frequencies and wavelength. Its not necessarily in phase either...

This will just result in lots of destructive interference and you probably won't get a pattern with any symmetry.

If you want to carry out this experiment just use candle light, that's how it was first done i believe.
 
  • #3
I'm sure a candle's light is no more coherent than an electric bulb's. Also, I understand collimating a light source will basically always increase the coherence length. Kind of like saying the light that passes through the first slit must be coherent with itself to some degree, but probably wouldn't of been as coherent with the light that struck a centimeter left of that slit.
 
  • #4
thank you for the explanation.
But how can the light for the light bulb becomes coherent after a single slit ?
How can the slit change their wavelength and frequency and make them the same ?
 

What is the concept of Young's double slits experiment?

The Young's double slits experiment is a classic experiment in physics that demonstrates the wave-like nature of light. It involves shining a coherent light source, such as a laser, through two narrow slits to create an interference pattern on a screen.

How does the interference pattern in Young's double slits experiment form?

The interference pattern in Young's double slits experiment is created by the superposition of two coherent light waves from the two slits. When the waves meet, they interfere constructively or destructively, resulting in bright and dark fringes on the screen.

What is the significance of using coherent light in Young's double slits experiment?

Coherent light is used in Young's double slits experiment because it has a fixed phase relationship, meaning that the peaks and troughs of the light waves are in sync with each other. This allows for a clear and consistent interference pattern to form.

How does the distance between the slits affect the interference pattern in Young's double slits experiment?

The distance between the two slits, also known as the slit separation, affects the spacing of the interference pattern on the screen. A smaller slit separation results in a wider interference pattern, while a larger slit separation creates a narrower interference pattern.

Can Young's double slits experiment be used to determine the wavelength of light?

Yes, Young's double slits experiment can be used to measure the wavelength of light. By measuring the distance between the fringes on the screen and using the known distance between the slits, the wavelength of light can be calculated using the equation λ = d(sinθ)/n, where λ is the wavelength, d is the slit separation, θ is the angle between the screen and the central bright fringe, and n is the order of the fringe.

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