Answer: mu 0 nI.
- A mu<sub>0</sub> n
- B mu<sub>0</sub> nI
- C mu<sub>0</sub> I/n
- D mu<sub>0</sub> n<sup>2</sup> I
Correct answer: B. mu<sub>0</sub> nI
Explanation: Solenoid: B = mu<sub>0</sub> nI (n = turns per unit length). This is uniform inside a long solenoid.
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.