Modern Physics
Nuclear-scale confinement
For the 100 MeV photon at 1 fm, pγ = E/c is a momentum scale; Δp_min = ℏ/(2Δx), so Δx·Δp = ℏ/2 here.
Nuclear-scale confinement — interactive physics simulation. For the 100 MeV photon at 1 fm, pγ = E/c is a momentum scale; Δp_min = ℏ/(2Δx), so Δx·Δp = ℏ/2 here. Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Nuclear confinement
pγ = E/c differs from Δp_min = ℏ/(2Δx); here Δx·Δp = ℏ/2.
For the 100 MeV photon at 1 fm, pγ = E/c is a momentum scale; Δp_min = ℏ/(2Δx), so Δx·Δp = ℏ/2 here.
- ΔxΔp ≥ ℏ/2
- High momentum
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
If you tried to confine a photon to within a single atomic nucleus (about a femtometre across), the uncertainty principle demands an enormous minimum momentum uncertainty. Does this help explain why free electrons are never found INSIDE a nucleus?
Predictions to weigh
- The uncertainty principle doesn't apply at nuclear scales.
- Confinement to nuclear scale would require an unusually small momentum uncertainty.
- Yes — confining any light particle to nuclear scale would require momentum uncertainty (and therefore energy) far larger than what's actually observed escaping nuclei, ruling out electrons living inside.
Variable roles
What you set:
- Confinement region Δx (nm)
What you measure:
- Momentum uncertainty Δp (×10⁻²⁰ kg·m/s)
How the investigation runs
- Open the gamma-confinement preset and press Reset. This preset models a 100 MeV photon confined near femtometre (10⁻¹⁵ m) scale.
- Enable the minimum-momentum-uncertainty readout.
- Set the confinement region Δx for each trial (near nuclear scale) and record the minimum possible momentum uncertainty.
Governing equation
Uncertainty at Nuclear Scale — Δx·Δp ≥ ℏ/2
Confining any particle — including a massless photon — to within Δx ≈ 10⁻¹⁵ m demands a minimum momentum uncertainty Δp ≥ ℏ/(2Δx) on the order of 10⁻²⁰ kg·m/s, corresponding to energies far exceeding what's observed for particles actually found inside nuclei.
What the printable worksheet asks students to work out
- For one trial, compute Δp_min = ℏ/(2Δx) using ℏ = 1.055×10⁻³⁴ J·s. Compare to the table — notice these values are about 10⁵ times larger than the heisenberg-electron experiment's, because Δx here is about 10⁵ times smaller.
- For a photon, momentum relates to energy by p = E/c. Explain how converting your Δp_min values to an equivalent minimum energy uncertainty (multiply by c) helps justify why particles confined to nuclear dimensions must carry enormous minimum energy — tens of MeV, matching this experiment's 100 MeV photon.
Where this shows up beyond the lab
- Historically, physicists once wondered if electrons emitted in beta decay were 'stored inside' the nucleus beforehand. This uncertainty-principle argument (electrons confined to nuclear scale would need far more energy than beta-decay electrons actually have) was key evidence that electrons are instead CREATED at the moment of decay, not pre-existing inside the nucleus.
- Unlike the electron in heisenberg-electron, this experiment explicitly models a massless photon, using momentum p = E/c instead of p = √(2mK). Explain why a photon's momentum formula has to be different from a massive particle's.
- 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 Gamma Confinement
- Select the uncertainty setup
- Press Play
- Nuclear size limit
- 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.