Stationary waves
Cambridge A-Level Physics (9702) · Unit 8: Superposition · 8 flashcards
Stationary waves is topic 8.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 8 — Superposition , alongside Diffraction, Interference and The diffraction grating. In one line: When two or more waves overlap in a region, the resultant displacement at any point is the vector sum of the displacements of the individual waves at that point.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 8 flashcards — 3 definitions, 4 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Principle of superposition
When two or more waves overlap in a region, the resultant displacement at any point is the vector sum of the displacements of the individual waves at that point.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Explain the principle of superposition and use it.
- Understand experiments in which stationary waves are produced with stretched strings, air columns and microwaves. Treat end corrections as negligible; you do not need to know what an end correction is.
- Explain, using a graphical method, how a stationary wave forms, and identify where its nodes and antinodes are.
- Understand how a stationary wave's wavelength can be found from where its nodes or antinodes are.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Stationary waves
- › Distinguish between displacement (instantaneous) and amplitude (maximum). Nodes have zero amplitude and never move from the equilibrium position.
- › Define stationary waves as the superposition of two waves of the same frequency and amplitude traveling in opposite directions.
- › The principle of superposition states the resultant displacement is the sum of the individual displacements of the waves at that point.
- › Ensure your stationary wave model includes a node at the reflecting surface; count all nodes and antinodes carefully to determine the correct wavelength.
- › Remember that in a stationary sound wave, the distance between successive nodes (quiet spots) is exactly half a wavelength.
State the principle of superposition.
When two or more waves overlap in a region, the resultant displacement at any point is the vector sum of the displacements of the individual waves at that point.
Describe how stationary waves are formed.
Stationary waves are formed when two progressive waves, travelling in opposite directions, with the same frequency and amplitude, superpose. Interference results in points of maximum displacement (antinodes) and zero displacement (nodes).
What is the distance between two adjacent nodes (or antinodes) in a stationary wave?
The distance between two adjacent nodes (or antinodes) is half the wavelength (λ/2) of the wave.
Explain how a stationary wave can be produced using microwaves.
Microwaves are directed at a metal plate, causing reflection. The incident and reflected waves, having the same frequency and amplitude, superpose to form a stationary wave. A microwave detector can be used to locate nodes and antinodes.
Describe an experiment to demonstrate stationary waves using a stretched string.
A string is attached to a vibration generator at one end and passes over a pulley with a hanging mass at the other. By adjusting the frequency of the vibration generator, standing waves are created when an integer number of half-wavelengths fit along the string. The frequency at which resonance occurs is noted.
Explain how you can determine the wavelength of a stationary wave from the positions of its nodes.
Measure the distance between several nodes, then divide by the number of internodal distances to find the average internodal distance. Since the distance between adjacent nodes is λ/2, multiply the internodal distance by 2 to find the wavelength λ.
What is the difference between a node and an antinode in a stationary wave?
A node is a point on a stationary wave where the displacement is always zero (destructive interference). An antinode is a point on a stationary wave where the displacement has maximum amplitude (constructive interference).
How are stationary waves in air columns formed?
Stationary waves can form in air columns (
Review the material
Read full revision notes on Stationary waves — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 8 — Superposition
Stationary waves sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Stationary waves deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Stationary waves deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Rate each card Hard, Okay, or Easy after flipping.