Standing Waves
Waves trapped between boundaries form nodes and antinodes.
About this topic
A standing wave forms when two identical waves travel in opposite directions, typically a wave and its reflection, producing fixed points of zero motion (nodes) and points of maximum motion (antinodes). Only certain wavelengths fit: for a string fixed at both ends, λ = 2L/n.
These give the harmonics: the fundamental has frequency f₁ = v/2L, and higher modes are whole-number multiples, f_n = nf₁. Guitar strings, organ pipes, flutes and drum skins all rely on standing waves, and the pitch of a string depends on its length, tension and mass per length. Shortening the string with a finger raises the pitch.
Worked example: a string 0.65 m long with wave speed 260 m/s has fundamental f₁ = 260/(2 × 0.65) = 200 Hz, with further harmonics at 400 Hz, 600 Hz and so on. Between neighbouring nodes is half a wavelength. A tube open at both ends supports all harmonics, while one closed at one end supports only odd ones.
Microwave ovens have standing waves, which is why food heats unevenly and has a turntable. Lasers use standing light waves in a cavity. A misconception is that standing waves are not moving; the medium oscillates strongly at antinodes, and only the pattern stays still, with energy not travelling along.
Key ideas
- Nodes never move
- Guitar strings and organ pipes
- fₙ = n f₁
Quick check
Use cases: where Standing Waves helps
- Homework: review the key idea behind Standing Waves before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Standing Waves without notes.
- Visual learning: play with the interactive lab to see how Standing Waves changes when you adjust its inputs.
- Teaching a friend: explain Standing Waves 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 Standing Waves?
Waves trapped between boundaries form nodes and antinodes.
What will I learn in Standing Waves?
Nodes never move. Guitar strings and organ pipes. fₙ = n f₁.
Is Standing Waves 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 Standing Waves 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 Standing Waves?
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.