# Instructor guide: Wave-packet width and uncertainty record

Course: Quantum physics: states, amplitudes, and measurement

Suggested time: 45–60 minutes

## Learning target

Learners connect localization with momentum spread without treating a wavefunction as a literal material wave or hidden classical path.

## Prepare

- Review probability distributions and standard deviation.
- Distinguish central value from spread.
- Prepare repeated-measurement language before opening the model.

## Facilitation moves

- Ask what an ensemble of trials would show.
- Keep packet width separate from particle size.
- Require learners to name the free-particle idealization.

## Misconception checks

- **Uncertainty is only poor measurement technique.** The modeled quantum state itself can have irreducible spreads even with ideal measurement.
- **The wave packet is a tiny classical cloud with a hidden exact trajectory.** It encodes amplitudes for possible outcomes; interpretations add different ontologies beyond the shared predictions.

## Accessibility and participation

- Pair every graph with a numeric center-and-spread table.
- Describe widening verbally and avoid animation-only evidence.
- Permit spreadsheet calculations for standard deviations.

## Evidence of learning

- A controlled width comparison
- Correct center-versus-spread language
- One stated model limitation

## Extension

Compare free spreading with a confined packet and identify which Hamiltonian term changes the evolution.

## Evidence boundary

Assess the learner's reasoning only within the declared model and recorded observations. Do not upgrade a simulation result into a claim about an unmodeled physical system.