Answer: current.
- A current
- B charge
- C voltage
- D resistance
Correct answer: A. current
Explanation: ∮B·dl = μ₀I<sub>enclosed</sub>, relating the field to the enclosed current.
The magnetic field around a long straight current-carrying wire forms concentric circles, with direction given by the right-hand rule (point thumb along I, fingers curl in the direction of B).
Concept context
Magnetic force on moving charges and currents, the Biot-Savart law, Ampere's law, and the cyclotron - how electric currents create and respond to magnetic fields.