Modern Physics
Slow electron wave packet
Low K gives a long de Broglie wavelength on the λ-scale bench.
Slow electron wave packet — interactive Modern Physics simulation. Low K gives a long de Broglie wavelength on the λ-scale bench. Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Long wavelength electrons
Low K gives a long de Broglie wavelength on the λ-scale bench.
Low kinetic energy means small momentum and long de Broglie wavelength, so diffraction and interference effects dominate over particle-like paths. This preset uses slow electrons so λ is large on the bench and wave behavior is obvious.
- λ = h/p
- Low K → long λ
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
A slow-moving electron has a longer de Broglie wavelength than a fast one. Does this mean a slow electron's wave nature is easier or harder to observe experimentally?
Predictions to weigh
- Harder to observe for slow electrons.
- Easier — a longer wavelength (comparable to atomic spacings or slit sizes) makes diffraction and interference effects more pronounced and detectable.
- Wave effects don't depend on the electron's wavelength.
Variable roles
What you set:
- Kinetic energy K (eV)
What you measure:
- De Broglie wavelength λ (pm)
How the investigation runs
- Open the slow-electron-wave preset and press Reset. These electrons move much slower than in the electron-de-broglie experiment.
- Enable the de Broglie wavelength readout.
- Set the electron's (low) kinetic energy for each trial and record its de Broglie wavelength.
Governing equation
De Broglie Wavelength at Low Energy — λ = h/p
Since λ = h/√(2mK), lowering an electron's kinetic energy increases its de Broglie wavelength — slow, 'cold' particles have the most pronounced, easiest-to-observe wave behavior.
What the printable worksheet asks students to work out
- For one trial, compute λ = h/√(2m_eK) using K in the 5-20 eV range. Compare to the table — notice these wavelengths (hundreds of pm) are longer than the higher-energy electron-de-broglie experiment's.
- Explain why lowering kinetic energy (lowering momentum) always increases the de Broglie wavelength, using λ = h/p.
Where this shows up beyond the lab
- The 1927 Davisson-Germer experiment scattered slow electrons (similar energies to this experiment, tens of eV) off a nickel crystal and observed a diffraction pattern matching exactly the predicted de Broglie wavelength — the first direct experimental confirmation of matter waves. Explain why slow electrons (with wavelengths comparable to atomic spacing in a crystal) were the right choice for this experiment.
- Techniques like laser cooling can slow atoms down to extremely low kinetic energies, giving them de Broglie wavelengths large enough to observe striking quantum wave effects (like Bose-Einstein condensates). Explain the general principle connecting 'colder' to 'more wave-like.'
- AP Physics 2 — Unit 15: Modern Physics
- IB Physics — E.2 Quantum physics
- General High School Physics — Modern physics intro
- NGSS High School Physics — Wave-particle duality of light
- Welcome to Slow Electron Wave
- Select the electron
- Press Play
- Long λ at low energy
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.