00:01
So we're going to look at the condition for constructive interference and destructive interference.
00:09
It's quite easy to understand.
00:11
So you have two sources and they are oscillating in phase.
00:17
How they get out of phase and recombine in an interfering way is when they follow two different paths.
00:27
And we'll call the sources a and b.
00:30
But if the difference in path length is an integer multiple of the wavelengths, then what will happen, so we'll call that m -lamda, what will happen is the two waves will travel two different distances, but they will come back together in phase with their wavelengths matching up so that the peak of one wave combines with the peak of another.
01:13
And so you get a much bigger peak when you add those two waves together.
01:19
You get a plus b, and you get a very intense reception there.
01:26
This is called constructive interference.
01:31
However, if the path, the difference in path lengths is equal to m plus one half foot a wavelength, then what will happen is that the crest on one will add up to the trough on the other.
01:58
So we'll try to draw that.
02:00
So here's a, and let's make it go half wavelength out compared to b.
02:12
And so if you add those two together, you get them washing out and equaling nothing.
02:22
Of that, of course, is destructive interference.
02:27
So what's really important is the path that they took in order to get to the observation point.
02:34
So let's take an example.
02:36
Let's say that we have two towers that are radiating the same wavelength and in phase, towers a and b, and our observation point is over there at point q.
02:48
How far does a go? it goes 160 meters...