A uniform current-carrying narrow solenoid produces

A solenoid consists of a long wire wound into a tight helical coil. When a steady electric current passes through a uniform narrow solenoid, it generates a magnetic field. Inside the solenoid, the magnetic field lines are nearly parallel to the axis and are spaced uniformly, which indicates that the magnetic field is uniform (constant in magnitude and direction) throughout the interior volume. In contrast, the magnetic field outside the solenoid is non-uniform and significantly weaker, theoretically approaching zero for an infinitely long solenoid. The field lines outside curve from the north pole to the south pole, similar to a bar magnet. Therefore, the solenoid produces a uniform magnetic field specifically inside its core.