# Instructor guide: Two-source field map

Course: Matter, energy, fields, and forces

Suggested time: 40–50 minutes

## Learning target

Learners add field contributions as vectors and distinguish a field map from material lines in space.

## Prepare

- Review sign conventions for a positive test charge.
- Sketch one symmetric two-source arrangement.
- Plan a no-calculator vector-addition checkpoint.

## Facilitation moves

- Ask for direction before magnitude.
- Require learners to name the test object convention.
- Compare a cancellation point with a point merely far from both sources.

## Misconception checks

- **Field arrows are physical threads.** They encode the force direction and scale that a test charge would experience locally.
- **Zero net field means no sources exist.** Nonzero contributions can cancel at a particular location.

## Accessibility and participation

- Pair color with arrow direction and numeric labels.
- Use tactile arrows or cut paper vectors when useful.
- Do not require fine pointer placement; keyboard control is equivalent.

## Evidence of learning

- Correct component-vector diagram
- A controlled sign-reversal comparison
- Explanation of one model boundary

## Extension

Compare field cancellation with potential addition at the same point.

## 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.