Video: Wave Interference

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Wave Interference

 
 
Interference occurs when two pulses meet while traveling in opposite directions along the same medium. There are two types of interference – constructive and destructive. Constructive interference occurs when both pulses displace the medium in the same direction – both upward or both downward. Destructive interference occurs when the displacement is in opposite directions.
 
This diagram shows two waves interfering. The rules for constructive and destructive interference are the same for waves as they are for pulses. Points A and F represent constructive interference since each wave is displaced upward at these locations. Point C represents constructive interference since each wave is displaced downward at this location. But points B, D, and E represent destructive interference since the medium is displaced in opposite directions by each wave at these locations.
 
Wave interference causes the displacement of the medium to be momentarily changed. The resulting displacement at any location can be predicted using the principle of superposition. It would be the sum of the displacements caused by each individual wave. For instance, the displacement of the medium at point A would be +8 units since the blue wave causes a +6 unit displacement and the red wave causes a +2 unit displacement. At point B, the resultant displacement is +4 units since the blue wave causes a +6-unit displacement and the red wave causes a -2 unit displacement. By applying the principle of superposition to several points along the medium, you can determine the displacement at each location and an estimated shape of the resultant wave at that moment in time. This is shown in the diagram.
 
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