Destructive interference happens when one
wave is oscillating the opposite way as the other one, so it compensates.
For example:
Let’s say one wave can be described with
this formula:
f(x)=sinx
And the other one, with this formula:
g(x)=-sinx
So when you add them, you get 0 for any x
value:
h(s)=f(x)+g(x)=sinx-sinx=0
(I recommend to put them in a graph
software such as GeoGebra, to see how they look like).
In other cases, the sum of both can be
bigger than each one of them. That is called constructive interference. For
example:
Wave 1: f(x)=sinx
Wave 2: g(x)=2sinx
Total: h(x)=f(x)+g(x)=sinx+2sinx=3sinx
which is bigger than sinx, and also higher
to 2sinx, for any x value.
If you have the graph instead of the
formula, take 2 points from the graph which have the same x value, one in the
first wave and the other one in the second wave, and add them (y1+y2). If both numbers
are the same but one is negative and the other one is positive, the sum will be
0, and that is a destructive interference.
