Wave interference review

When two pulses overlap, we need to add each individual pulse’s displacement to determine the shape of the resulting pulse.

We get constructive interference when pulses have the same direction of displacement from equilibrium at the same position. If two pulses are completely overlapping, the resulting pulse has an amplitude that is the sum of the amplitudes of each individual pulse.

We get destructive interference when pulses have displacements from equilibrium that are in opposite directions. If the two pulses are completely overlapping, the resulting pulse has a smaller amplitude than either individual pulse. If the pulses have the same amplitude but opposite displacement, then the resulting pulse has zero amplitude.

1. Sometimes people forget that amplitudes add up at every point. When pulses meet, the different parts of the pulses can have constructively or destructively interference depending on their relative displacements from equilibrium.

2. People sometimes forget that constructive pulses don't reflect off each other. If we look at wave pulses with displacement in opposite directions, we can tell the pulses continue moving in the same direction after they overlap. The same phenomenon occurs for constructive interference.

For deeper explanations of superposition, see our video on wave interference.

To check your understanding and work toward mastering these concepts, check out the exercise on predicting wave interference patterns.