Use field superposition to predict force and potential patterns
Three steps, the way the exam actually works: work through the lab, write down your own observations, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own evidence will cost you the point — exactly as it would with a real reader.
Predict before you look
- Field is a vector sum and potential is a signed scalar sum. Which of the two can cancel to zero while the other does not?
- Between two charges of opposite sign, do the two field contributions point the same way or opposite ways?
Nothing to submit here — these are to think through, so the prediction below is an informed one rather than a guess.
Commit to an answer now. It is not graded and being wrong costs nothing — the point is to have something specific to reconcile against once you have the data.
Answer every prediction to unlock the lab. A sentence is enough.
Run the investigation
Predictions first
The procedure and the simulation unlock once you have committed above. Observing before predicting is how a wrong intuition survives a lab intact.
Record what you found
This is your reading of the source, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| Field pattern for one positive charge | |
|---|---|
| Pattern between two like charges | |
| Pattern between opposite charges | |
| Where the net field became small |
Answer the free response
Electric fields add by superposition. (a) Explain why the field lines point away from a positive charge and toward a negative charge using the definition of electric field. (b) Compare the region between two like charges with the region between opposite charges, and explain what superposition predicts in each case. (c) Distinguish electric field from electric potential using one of the patterns you observed. (d) A student says a test charge is needed to “create” the field. Evaluate that claim carefully.
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