Short Answer
Carrier density and sign in a conductor is the best answer.
Electromagnetism questions become manageable once you separate source, field, potential, current, and force. Most wrong answers mix those layers together or ignore direction.
The Hall effect produces a transverse voltage when current-carrying conductor is in a magnetic field; it reveals carrier type and density.
Why This Answer Is Correct
This is a Medium-level question in Electromagnetism. The prompt is really testing whether you can connect the concept to its defining physical relationship instead of picking a nearby-but-wrong term.
Keep charge, field, potential, and current distinct. That single habit fixes a large fraction of electromagnetism errors.
Choices At A Glance
- A. Temperature
- B. Carrier density and sign in a conductor
- C. Frequency of AC current
- D. Magnetic monopole strength
When similar options appear on an exam, eliminate the ones that break the core law, use the wrong units, or confuse a definition with a consequence.
Topic Snapshot
Topic: Electromagnetism
Difficulty: Medium
Best next move: Re-state the governing law in your own words, then solve one more example from the same topic before moving on.