The document discusses the magnetic effects of electric current. It begins by explaining Oersted's experiment which showed that electric current produces a magnetic field. It then provides several rules for determining the direction of magnetic fields, including Ampere's swimming rule, Maxwell's corkscrew rule, and the right hand thumb rule. Biot-Savart's law is introduced to quantify the magnetic field produced by a current-carrying element. Expressions are derived for the magnetic fields produced by an infinitely long straight wire, a circular loop, and a solenoid.