Basic Electromagnetism

This chapter introduces basic electromagnetism, starting from the simple attractive (or repelling) force between magnets. It defines magnetic field, dipole moment, torque, and magnetic energy and its equivalence to current. Magnetic poles exert magnetic force to each other, like electric charges. In any magnetic materials, its magnetic poles always come in pairs: the north and south poles. The positive and negative poles show up in the same time and form a dipole. The magnetic flux is an important parameter in electric motor and generator design. The chapter describes the calculation of magnetic field from electrical current elements. For current flowing in a special path, Ampère's circuital law can provide a closed‐form solution. For current flowing in a more complex geometry, the magnetic field at a position can be handled by Biot‐Savart's law. Both Ampère's law and Biot‐Savart's law connect magnetic field and electrical current in a vacuum.