The magnetic field of the infinite solenoid is calculated using a new method. An infinitely long
charged line moving along a closed curve on the plane perpendicular to the infinite line will
generate an electric current and so the magnetic field of the infinite solenoid. Through the
electric–magnetic field relation, the magnetic field of the infinite solenoid is simply obtained and
the reason why the magnetic field is a constant is clearly shown. Further, Ampere’s circuital law is
analyzed from the particle point of view using the electric–magnetic field relation. These
discussions are helpful to the understanding of the magnetic field of the infinite solenoid and
Ampere’s circuital law for students and teachers of electromagnetism.