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Wave interference review

Review the key terms and skills related to wave interference, including how to predict wave interference patterns. 

Key terms

TermMeaning
PulseA single disturbance that moves through a medium.
InterferenceWhat occurs when two or more waves pass through one another. Also called superposition.
Constructive interferenceWhen overlapping waves produce a wave with an amplitude that is the sum of the individual waves.
Destructive interferenceWhen overlapping waves produce a wave with an amplitude that is less than the sum of the individual waves.

How to predict interference for two pulses

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

Constructive interference

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.
Figure 1: Constructive interference for two pulses.

Destructive interference

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.
Figure 2: Destructive interference for two pulses.

Common mistakes and misconceptions

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.

Learn more

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.

Want to join the conversation?

  • piceratops seed style avatar for user Jett Harrison
    how does the superposition principle differ from quantum superposition? are there any similarities or conceptual overlap?
    (4 votes)
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  • blobby green style avatar for user farinaburhan.11
    is pulse and superposition same?
    (2 votes)
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    • eggleston blue style avatar for user IsotonicFlaccidCell21
      No, a pulse is a single disturbance in a wave. Superposition, however, is when two pulses cancel out each other. A pulse's amplitude may be 50m at one point in time, but if there is a pulse which has an amplitude of -50m at the same time, they will cancel out and nothing will be heard, that is how noise-cancelling headphones work.
      (4 votes)
  • male robot donald style avatar for user Aaron Ghosh
    What would happen if a wave "interfered" with another wave at the end of a sting? This string would be connected to a wall with 2 screws, so that when a wave hits the screw, it bounces back, i.e. the pulse(s) never stop. So, if there are 2 pulses that "interfere" with one another at a point where half of each of the pulses is going to the right, and half is being reflected back left, what would the resulting wave be?
    (3 votes)
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  • leafers sapling style avatar for user camden.baxter0707
    are you going to fix the hacks
    (1 vote)
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  • blobby green style avatar for user GomezRoy
    thats a good way of describing the problem
    (1 vote)
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  • aqualine ultimate style avatar for user TrystonGarrison
    N o t h a n k s
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  • aqualine ultimate style avatar for user JaraeJ
    Which wave length
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