Wave interference

Wave interference happens when two waves overlap to form an interference pattern. The amplitude of the resulting wave may be increased, decreased or neutralized.

Wave interference

Overlapping waves can create two types of interference. The interference could be a constructive interference or a destructive interference.

Constructive wave 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 above 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 above.

They will then create the resulting constructive interference wave shown in orange below.

Notice that the height of the orange crest is as high as the height of the blue crest + the green crest.

By the same fashion, the height of the orange trough is as high as the height of the blue trough + the green trough.

Constructive interference

Destructive wave interference


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. 

Destructive wave interference

If you keep moving them toward each other, you end up with the graph above. If the height of the crest is the same as the trough after the interference, there will be a cancellation or neutralization.The cancellation is shown with a red line and a brown line.

Destructive interference

Other situations of wave interference

Sometimes a little height is added or removed. It depends on the situation. This is illustrated in the image to follow.

Constructive and destructive interference
  • The red crest is the result of adding the blue crest and the green crest. The amplitude of the blue trough has been increased.
  • The red trough is the result of subtracting the green crest from the blue trough. The amplitude of the blue trough has been decreased.

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