00:02
Let's go over the difference between constructive versus destructive interference.
00:10
So the idea is you have two sources of waves, and we'll assume that they are in phase, and i'll draw them on a line just to make things a little bit easier.
00:24
So source one and source two.
00:27
And we'll assume that they start off in phase, which means they both.
00:32
Hit their peak of oscillation right at the source at the same time.
00:40
And what we're looking at is the waves that combine somewhere in space around those two sources.
00:52
So maybe our position one, our position two, it really does not matter.
01:00
But the two waves go through a different distance.
01:08
So that's called a path length.
01:09
I'll call that path length one and path length two.
01:14
If the two waves come together such that their peaks concur in time, that is called constructive interference.
01:30
So the peaks match up and the troughs match up.
01:33
That is called constructive interference.
01:39
And that happens when the path length difference, so absolute value of path length two, minus path length one.
01:49
So one is going to be bigger than the other, and it doesn't really matter.
01:53
But if that is some integer multiple of the wavelength of the wave, so m is an integer, one, two, three, because we're taking an absolute value, we're assuming that the integer is positive, but if we just wrote it as the difference, the m could be a negative integer as well.
02:19
So if the path length difference is an integer multiple of wavelength, then you have constructive interference.
02:28
If the path length difference is a half integer multiple of the wavelength, then what's going to have happen is your trough on one wave will hit the crest on another and you get destructive interference.
02:53
So path length 2 minus path length 1 is equal to m plus 1 half lambda, with again m being an integer of some sort.
03:14
Okay, but there.
03:15
Waves are shifted by a half a wavelength when they come back together.
03:21
So let's take an example.
03:24
Here we're going to be looking at sound waves with a particular wavelength.
03:31
So we have our sources and they are separated by distance d.
03:37
So we'll call those source one and source two.
03:47
And what we know is when they are right on top of each other, if d is equal to zero, there is constructive interference at the detector.
04:07
So we have a detector over, looks kind of like an eyeball that will draw on here there.
04:16
Detector.
04:22
And what that tells us is the two waves are emitting in phase.
04:30
So the two sources are in a good spot in terms of being able to figure things out they are in phase.
04:45
So that the only thing that is going to determine what happens at the detector is the two different paths that they travel...