Wave-particle duality
Cambridge A-Level Physics (9702) · Unit 22: Quantum physics · 7 flashcards
Wave-particle duality is topic 22.3 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 22 — Quantum physics , alongside Energy and momentum of a photon, Photoelectric effect and Energy levels in atoms and line spectra. In one line: The de Broglie wavelength (λ) is the wavelength associated with a moving particle, relating its momentum to its wave-like properties. It shows that particles, such as electrons, also have a characteristic wavelength.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 7 flashcards — 1 definition, 4 key concepts and 2 calculations — covering the precise wording mark schemes reward. Use the definition card 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.
The de Broglie wavelength
The de Broglie wavelength (λ) is the wavelength associated with a moving particle, relating its momentum to its wave-like properties. It shows that particles, such as electrons, also have a characteristic wavelength.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · A2 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).
- Understand that the evidence for electromagnetic radiation having a particulate nature comes from the photoelectric effect, and evidence for its wave nature from effects such as diffraction and interference.
- Describe, and interpret qualitatively, how electron diffraction provides evidence that particles have a wave nature.
- Understand that any moving particle has an associated wavelength, called its de Broglie wavelength.
- Recall λ = h/p and use it.
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 Wave-particle duality
- › Specifically state that diffraction is evidence for the wave nature of moving electrons; it does not demonstrate particle nature.
Describe the evidence that the photoelectric effect provides for the particulate nature of electromagnetic radiation.
The photoelectric effect demonstrates that light energy is delivered in discrete packets called photons. Electrons are emitted instantaneously only when the photon energy exceeds the work function, suggesting a particle-like interaction rather than a continuous wave absorption.
Explain how electron diffraction provides evidence for the wave nature of particles.
Electron diffraction, similar to X-ray diffraction, produces interference patterns when electrons pass through a crystal lattice. This demonstrates that electrons, traditionally considered particles, exhibit wave-like behavior by undergoing diffraction and interference.
Define the de Broglie wavelength.
The de Broglie wavelength (λ) is the wavelength associated with a moving particle, relating its momentum to its wave-like properties. It shows that particles, such as electrons, also have a characteristic wavelength.
State the formula for the de Broglie wavelength and define each term.
λ = h / p, where λ is the de Broglie wavelength, h is Planck's constant (6.63 x 10⁻³⁴ Js), and p is the momentum of the particle (p = mv, where m is mass and v is velocity).
Calculate the de Broglie wavelength of an electron with a momentum of 1.0 x 10⁻²⁴ kg m/s.
Using λ = h / p, where h = 6.63 x 10⁻³⁴ Js and p = 1.0 x 10⁻²⁴ kg m/s, then λ = (6.63 x 10⁻³⁴) / (1.0 x 10⁻²⁴) = 6.63 x 10⁻¹⁰ m or 0.663 nm.
Explain why macroscopic objects do not display noticeable wave-like behavior.
Due to their large mass, macroscopic objects have very small de Broglie wavelengths (λ = h/mv). These wavelengths are so small that diffraction and interference effects are negligible and undetectable in everyday observations.
Describe how increasing the momentum of a particle affects its de Broglie wavelength.
Increasing the momentum of a particle decreases its de Broglie wavelength. Since λ = h/p, wavelength is inversely proportional to momentum. A higher momentum results in a shorter wavelength.
Review the material
Read full revision notes on Wave-particle duality — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 22 — Quantum physics
Wave-particle duality 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 Wave-particle duality deck
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