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Another example is going to be
as follows: this time we have a green laser, so wavelength is a little shorter
it goes through 2 slits again, and we get some interference pattern that's 2 m away
you measure the distance between two adjacent bands, center to center, is 1 cm, how far apart are the slits
this time it's a little different, we are looking for how far apart the slits are, so we are not given that
and also, we are not looking for the distance to a specific band, we are talking about adjacent bands
let's quickly draw that out
once again we have the slits separated by a certain distance d, this time we know L = 3 m
and then the screen is back here and we have the distance between adjacent slits, so we have ...
so these things are regularly spaced as we have talked about for the bright fringes
so basically, this is a regular spacing, recall
if we are talking about y, ...
...
as you increase from one fringe to another, you are increasing n by 1 so ...
....
...
...
and so now we have everything, ...
...
...
...
so even they don't tell you a specific band to look for, you can
relate the fact that
these bands come at a regular interval
in order to figure these things out
so so much for today, we are going to continue on to talk about
adding up more than two slits
and also to add up an infinite number of slit to represent a single slit
You will see how all that works. We'll see you in the lecture