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
Official 2025-2027 spec · AS LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- explain and use the principle of superposition
- show an understanding of experiments that demonstrate stationary waves using microwaves, stretched strings and air columns (it will be assumed that end corrections are negligible; knowledge of the concept of end corrections is not required)
- explain the formation of a stationary wave using a graphical method, and identify nodes and antinodes
- understand how wavelength may be determined from the positions of nodes or antinodes of a stationary wave
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
- › Always use the relationship Intensity ∝ (Amplitude)² for any question involving the power or brightness of a wave.
- › In the equation d sinθ = nλ, always use the angle θ relative to the original path of the light.
- › Apply the condition for destructive interference: path difference equals (n + 1/2)λ. For a second-order dark fringe, the path difference is 3/2λ.
- › The principle of superposition states the resultant displacement is the sum of the individual displacements of the waves at that point.
- › In double-slit explanations, always state that waves must diffract at the slits to overlap and interfere.
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.
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