Superposition and Interference
Overlapping waves add together.
About this topic
When waves overlap, the displacement at each point is the sum of the individual displacements, the principle of superposition. Constructive interference occurs when crests meet crests, giving a bigger wave; destructive interference occurs when crests meet troughs and they cancel.
Whether waves reinforce or cancel depends on their path difference: a whole number of wavelengths gives constructive interference, and an odd number of half wavelengths gives destructive. After overlapping, the waves continue unchanged, which shows they don't permanently affect one another. Sources must be coherent, with a constant phase relationship, to give a steady pattern.
Worked example: two loudspeakers playing the same 343 Hz tone, with wavelength 1 m, produce loud spots where your distances to them differ by 0, 1 m, 2 m, and quiet spots where they differ by 0.5 m, 1.5 m. Walking in front of them you hear the loudness rise and fall.
Noise-cancelling headphones use destructive interference, generating sound that is the inverse of the background noise. Thin films such as soap bubbles show colours from light interfering, and concert halls are designed to avoid dead spots. A misconception is that destructive interference destroys energy; it is redistributed to places of constructive interference.
Key ideas
- Constructive: crests meet crests
- Destructive: crest meets trough
- Noise cancelling uses it
Quick check
Use cases: where Superposition and Interference helps
- Homework: review the key idea behind Superposition and Interference before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Superposition and Interference without notes.
- Visual learning: play with the interactive lab to see how Superposition and Interference changes when you adjust its inputs.
- Teaching a friend: explain Superposition and Interference in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Superposition and Interference?
Overlapping waves add together.
What will I learn in Superposition and Interference?
Constructive: crests meet crests. Destructive: crest meets trough. Noise cancelling uses it.
Is Superposition and Interference part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Superposition and Interference lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Superposition and Interference?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.