# Learner lab record: Faraday induction polarity map

Course: Electricity, magnetism, and Maxwell's picture

Name: ____________________  Date: ____________________  Group: ____________________

## Investigation question

How do flux-change rate and direction determine the magnitude and sign of an induced voltage?

## Setup

Use the induction laboratory. Keep coil geometry fixed, compare slow and fast flux changes, then reverse the direction without changing the magnitude.

## Variables

| Variable | Role | Unit |
| --- | --- | --- |
| Magnetic flux change | independent | Wb |
| Change duration | independent | s |
| Coil turns | controlled, then independent | turns |
| Induced emf | dependent | V |

## Predict before changing controls

1. Predict what doubling the change rate does to emf magnitude.

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2. Predict what reverses when the flux-change direction reverses.

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## Observation table

| turns | Δflux | Δtime | change direction | emf | polarity |
| --- | --- | --- | --- | --- | --- |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |

## Analyze

1. Which pair isolates change rate?

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2. Which pair isolates direction?

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3. How does Lenz's law protect the energy ledger?

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4. What apparatus property is absent from this ideal model?

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## Evidence-bounded conclusion

When flux changed ___ times faster, emf changed from ___ to ___; reversing the change reversed ___ because ___.

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