Let’s review interference and nodes for a minute…

How waves interact with each other depends on whether the waves are in phase or not. If they are in-step (in phase) with each other, then it’s easy to add up to double the displacement (constructive interference). If they are completely out of step, then they cancel each other out (destructive interference). We’ve seen this for transverse waves, but what about compression waves, like for sound waves?

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When sound waves travel through a medium, it will pull particles together at the compression section and push particles apart at the rarefaction section. The interference that happens here is similar to longitudinal wave interference, in that where two compression sections meet, they pull the particles together even more to generate a greater pressure area, which is constructive interference. The sound will be much louder at this location.

When two rarefaction sections of the wave meet up, they both push the particles further apart, generating a lower pressure area where the waves are also interfering constructively.

If you have sections where the waves interact to make areas of very high and very low pressures, then the sound loudness will increase. These types of areas are called anti-nodes. An antinode is where the wave is at its maximum.

Click here to go to next lesson on Interference Pros and Cons.

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