Wave interference happens when two waves overlap to form an interference pattern. The amplitude of the resulting wave may be increased, decreased or neutralized.
Overlapping waves can create two types of interference.
The interference could be a constructive interference or a destructive interference.
Constructive interference occurs either when one crest of one wave overlaps the crest of another wave or the trough of one wave overlaps the trough of another.
After the two waves below interfere, they will form a constructive interference.
Notice also that they are in phase with each other. This means that if we keep moving them toward each other, one will be on top of the other as shown below.
They will then create the resulting constructive interference wave shown in red. Notice that the height of the red crest is as high as the height of the blue crest + the green crest.
By the same fashion, the height of the red trough is as high as the height of the blue trough + the green trough.
Destructive interference occurs when one crest of one wave overlaps the trough of another wave. In this case, the waves are out of phase with each other.
If you keep moving them toward each other, you end up with the following graph. If the height of the crest is the same as the trough, there will be a cancellation or neutralization.
The cancellation is shown with a red line and a brown line
Sometimes a little height is added or removed. It depends on the situation. This is illustrated in the image to follow.
The red crest is the result of adding the blue crest and the green crest.
The red trough is the result of subtracting the green crest from the blue trough. The amplitude of the blue trough has been decreased.