An electromagnetic field (also EMF or EM field) is a physical field produced by the movement of electrically charged objects.
Illustration of electric and magnetic field. The electric field is present when the lamp is plugged in, due to the voltage difference between the connectors. The magnetic field is only present when the lamp is switched on, because that's when current flows in the cable. Source: Hydro-Québec
All around the world, people are constantly exposed to electromagnetic waves. Examples of man-made sources:
Examples of natural sources:
Electric and magnetic fields are also present in electromagnetic radiation. Electromagnetic radiation has a magnitude (size) and a frequency (time-dependent periodic variation). The frequencies of electromagnetic radiation ranges from static electric and magnetic fields, through radiofrequency and infrared radiation, to x-rays. The European power frequency is 50 Hz.
Published July 27, 2012
B and H both describe the magnetic field. The quantities B and H are related to each other by the magnetic permeability (µ) of the medium that they exist in.
where µ is the magnetic permeability. For air and human tissues µ is approximately 4π x 10-7 H/m.