Short Answer
σ = ne²τ/m 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.
Drude conductivity σ = ne²τ/m, where n is electron density, τ is collision time, m is electron mass.
Why This Answer Is Correct
This is a Hard-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. σ = ne²m/τ
- B. σ = ne²τ/m
- C. σ = nτ/me
- D. σ = m/(ne²τ)
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: Hard
Best next move: Re-state the governing law in your own words, then solve one more example from the same topic before moving on.