Why Do Some Light Sources Show Clear Interference Patterns While Others Do Not?

[Trollfaz]

Why is it that when I conduct the double slit experiment at home by shining light through 2 slits, I get no interference pattern but certain experiments are able to produce it?

 

[Orodruin]

What source are you using and how are your slits constructed?

 

[Trollfaz]

Flashlight and the slits are made from 2 holes in the paper

 

[Orodruin]

That is never going to work. You need a coherent, preferably monochromatic, light source (read "laser") and a slit separation comparable to the wavelength (order micrometer).

 

[Trollfaz]

Why is it that the air molecules don't cause the light to switch to a particle behaviour, like the.electrons？

 

[Nugatory]

Why is it that the air molecules don't cause the light to switch to a particle behaviour, like the.electrons？

The interaction between light and air is very weak, so visible light in air behaves pretty much as if it were in a vacuum. Free electrons on the other hand interact with just about everything', including random air molecules.

(Also, be aware that the double-slit experiment is not explained by saying that light or anything else switches between wave and particle behavior; that idea predates the modern development of quantum mechanics and is no longer used seriously).

 

[Lord Jestocost]

Why is it that when I conduct the double slit experiment at home by shining light through 2 slits, I get no interference pattern but certain experiments are able to produce it?

Look at https://www.physicsforums.com/threads/recreating-double-slit-experiment-without-laser.740901/

 

[sophiecentaur]

Why is it that when I conduct the double slit experiment at home by shining light through 2 slits, I get no interference pattern but certain experiments are able to produce it?

If you take a thin piece of glass (microscope slide is ideal but the glass from a photo frame could do) deposit a layer of carbon ("lamp black") on it from a candle flame. Then scratch two very parallel lines on it, as close together as you can get with a fine needle (some practice is needed for this). Then shine the light from a cheapo laser pointer through it. It will give you a very convincing set of interfering fringes.
The sizes are right and the coherence of the light source is right so that should do the job.

 

[Orodruin]

Then scratch two very parallel lines on it, as close together as you can get with a fine needle (some practice is needed for this).

Or you could just buy a diffraction grating or use a CD to achieve the same type of effect.

 

[sophiecentaur]

Agreed but the pattern is significantly different. Plus, it's nice to make your own kit if you can.
With a laser pen you can get all sorts of diffraction effects. Thin oil films, bubbles, fine machine threads. Exciting stuff.

 

[ZapperZ]

Why is it that when I conduct the double slit experiment at home by shining light through 2 slits, I get no interference pattern but certain experiments are able to produce it?

Actually, you DO get an interference pattern with a "white light", or a non-monochromatic light. It is just not what you would expect had you use a monochromatic light. I just did this in class with my students using both a laser and a light bulb, using both a double slit and a diffraction grating.

A prism, a diffraction grating, and a double slit (among other things) will cause interference pattern for a particular wavelength of light. If you have just one wavelength in your light source, then you end up with clear, distinct pattern JUST for that wavelength. But if your light source consists of more than one wavelength, or in the case of white light, a "continuous" spectrum of wavelengths, then the device will produce interference pattern for EACH of those wavelengths simultaneously. So the interference patterns for each wavelength will sit on top of one another.

So yes, you do get interference pattern. You just don't get to decipher it as easily as you would if your source only has one wavelength.

Zz.