In 1820, the Danish scientist H.C. Oersted discovered that the magnetic needle near the wire carrying the current was deflected, thus revealing the basic relationship between electricity and magnetism, and giving birth to electromagnetism. Practice has shown that the strength of the magnetic field generated around an infinite wire with current is proportional to the magnitude of the current and inversely proportional to the distance from the wire. In the SI unit system, the magnetic field strength of an infinitely long wire carrying a current of 1 ampere at a distance of 1/(2π) meter from the wire is defined as 1A/m (ampere/meter); to commemorate Oersted's contribution to electromagnetism, In the CGS unit system, the magnetic field strength of an infinitely long wire carrying a current of 1 ampere at a distance of 0.2 cm from the wire is defined as 1Oe (Oersted), 1Oe=1/(4π)*103A/m, the magnetic field strength is usually given by H said.
