Answer: μ₀nI.
- A μ₀nI
- B μ₀I/2R
- C μ₀nI/2
- D μ₀I/2πr
Correct answer: A. μ₀nI
Explanation: For a long solenoid, B = μ₀nI, nearly uniform inside.
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.