Young's Double Slits: Coherent Light Explained

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Discussion Overview

The discussion revolves around the necessity of a single slit in the context of Young's double-slit experiment, particularly focusing on the coherence of light sources. Participants explore the characteristics of coherent light and the implications of using different light sources, such as bulbs and candles, in the experiment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the role of a single slit in ensuring that light reaching the double slits is coherent.
  • Another participant defines coherent light as having the same wavelength and frequency, and being in phase, arguing that standard bulbs emit light of various frequencies and wavelengths, leading to destructive interference.
  • A different participant challenges the idea that candle light is more coherent than electric bulb light, suggesting that collimating a light source increases coherence length.
  • One participant seeks clarification on how a single slit can make light coherent, questioning the mechanism by which the slit could change the wavelength and frequency of light.

Areas of Agreement / Disagreement

Participants express differing views on the coherence of light from various sources, with no consensus reached on the effectiveness of candle light versus bulb light or the role of the single slit in producing coherence.

Contextual Notes

Participants mention concepts such as coherence length and the phase relationship of light, but the discussion does not resolve the underlying assumptions about coherence and the effects of the single slit on light properties.

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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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.
 
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.
 
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 ?
 

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