How are alternating-current sources of EMF different from direct-current sources?
Some equipment can run on either alternating current (AC) or direct current (DC). If the equipment is plugged into a household wall socket, it is using AC electric current that reverses direction in the electrical wiring-or alternates-60 times per second, or at 60 Hz (in most parts of the United States). If the equipment uses batteries, then electric current flows in one direction only, from the batteries to the equipment. This produces a “static” or stationary magnetic field, also called a direct current field. Some battery-operated equipment can produce time-varying magnetic fields as part of their normal operation. AC electric power produces magnetic fields that can generate weak electric currents in humans. These are called induced currents. Much of the research on how EMFs may affect human health has focused on AC-induced currents. It should be noted, however, that very strong DC magnetic fields are present in some industrial environments and may be of concern for other reasons, s
