Answer: μ₀I/2πr.
- A μ₀I/2πr
- B μ₀I/2r
- C μ₀I/r
- D μ₀I/4πr
Correct answer: A. μ₀I/2πr
Explanation: For a long straight wire, B = μ₀I/2πr.
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.