--- title: "de Broglie Waves and Electron Diffraction" description: "If light can behave as particles then particles can behave as waves, with wavelength h divided by momentum. Electrons fired at a thin crystal give diffraction rings, which nothing but a wave can produ" canonical: https://lightmysky.com/learn/science/de-broglie-waves-and-electron-diffraction-mt_Y8NthsmPcv source: https://lightmysky.com/learn/science/de-broglie-waves-and-electron-diffraction-mt_Y8NthsmPcv.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # de Broglie Waves and Electron Diffraction If light can behave as particles then particles can behave as waves, with wavelength h divided by momentum. Electrons fired at a thin crystal give diffraction rings, which nothing but a wave can produce. Subject: Science · Area: Waves, Light & Sound · Ages 17 to 18 Page: https://lightmysky.com/learn/science/de-broglie-waves-and-electron-diffraction-mt_Y8NthsmPcv ## Ready when they can - Calculates a de Broglie wavelength from a momentum or from an accelerating voltage - Explains why the wave nature of a cricket ball is never noticed - Names electron diffraction rings as the evidence and says what raising the voltage does to them ## Lesson: When particles behave like waves If light can act as particles, particles can act as waves. Every moving particle carries a wavelength given by h divided by its momentum. An electron with momentum 6.63e-24 kg m/s has wavelength 1.0e-10 m, about one atom wide, since 6.63e-34 divided by 6.63e-24 equals 1.0e-10. **Example.** A 0.16 kg cricket ball rolling at 10 m/s has momentum 1.6 kg m/s, so its wavelength is about 4e-34 m. To show interference, a wave must meet an object near its own wavelength in size. Nothing that small exists, so the ball's wave nature stays hidden and it rolls in straight lines. Electrons are light enough for the effect to show. Fired at a thin crystal of graphite, they form diffraction rings, which nothing but a wave can produce. Raise the accelerating voltage and the electrons gain momentum, so their wavelength shortens and the rings shrink toward the centre. **Tip.** Track voltage changes in two hops. Kinetic energy follows the voltage directly, while momentum follows its square root. Quadruple the voltage and momentum doubles, so the wavelength halves. Halve the voltage instead and the wavelength grows by the square root of two. **Recap.** Matter carries wavelength h over momentum, visible only when the wavelength nears the size of the gaps it meets. ## Practice 12 questions on this page, each with its working shown. ## Needs first - [The Photoelectric Effect and the Work Function](https://lightmysky.com/learn/science/the-photoelectric-effect-and-the-work-function-mt_ADQK7WB2JN) - [Single-Slit Diffraction and the Limit of Resolution](https://lightmysky.com/learn/science/single-slit-diffraction-and-the-limit-of-resolution-mt_qiG0fGadBU) - [Energy Levels and Line Spectra](https://lightmysky.com/learn/science/energy-levels-and-line-spectra-mt_RlMCSDxE5q) ## Opens up - [The Wavefunction and the Born Probability Rule](https://lightmysky.com/learn/science/the-wavefunction-and-the-born-probability-rule-mt_elzmbBzmKE) - [The Schrodinger Equation and What a Wavefunction Says](https://lightmysky.com/learn/science/the-schrodinger-equation-and-what-a-wavefunction-says-mt_WCwbaO9rpR)