# Learner lab record: Wave-packet width and uncertainty record

Course: Quantum physics: states, amplitudes, and measurement

Name: ____________________  Date: ____________________  Group: ____________________

## Investigation question

How does narrowing a wave packet in position change its momentum spread and later evolution?

## Setup

Use the wave-packet laboratory. Compare broad and narrow packets while keeping the central momentum fixed, then follow their modeled spreading over time.

## Variables

| Variable | Role | Unit |
| --- | --- | --- |
| Initial position width | independent | model length |
| Central momentum | controlled | model momentum |
| Momentum spread | dependent | model momentum |
| Packet width over time | dependent | model length |

## Predict before changing controls

1. Predict which initial packet has the larger momentum spread.

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2. Predict which packet spreads more rapidly in the free-particle model.

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## Observation table

| initial width | central momentum | momentum spread | time | later width | uncertainty product |
| --- | --- | --- | --- | --- | --- |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |

## Analyze

1. Which comparison isolates initial width?

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2. Does uncertainty describe instrument carelessness or the modeled state?

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3. What does the probability distribution predict?

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4. Which model assumptions limit the result?

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## Evidence-bounded conclusion

Narrowing the initial packet from ___ to ___ changed momentum spread from ___ to ___ and later spreading by ___ because ___.

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