Distance between light source and slits in the double slit

[sqljunkey]

Hi,

Does the distance between the light source and the slits matter? Does the interference pattern change if you move the light source closer or further from the slits?

I read from this link that the collimation of the light changes with distance and that affects the interference pattern, and also the further the light source is the more impurities there will be between the light source and the slits and that will interfere with the pattern we see.

https://physics.stackexchange.com/q...ght-and-distance-between-the-slits-is-changed

 

[sophiecentaur]

Does the distance between the light source and the slits matter?

Yes. The simple formula assumes that the two sources are totally coherent. That means the optical path from the (Infinitely narrow) source slit is equal for the two slits (and across them). One way to ensure this is to have the source at great distance behind. Alternatively, a lens system can be used.
Using a laser source takes care of that and it also gives a good monochromatic wave which produces a good pattern.