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.
Run the investigation
- 1Place one positive charge and observe the field-arrow pattern around it.
- 2Add a second like charge and observe how the field changes between them.
- 3Replace the second charge with an opposite charge and compare the pattern again.
- 4Identify at least one region where the net field becomes small because contributions cancel.
Booting the lab…
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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