What are EMFs?
Electric and magnetic fields (EMFs*) exist all around us. We are constantly exposed to natural sources of EMFs, for example from the Earth’s electric and magnetic fields. We are also exposed to man-made sources of EMFs, from the low frequency EMFs associated with our power supply to higher frequency electromagnetic fields* used to transmit information, for example TV transmitters or mobile phone base stations.
One of the main defining characteristic of either electric or magnetic fields or electromagnetic fields is their frequency. This simply means the number of oscillations per second. We are mainly concerned with looking at the possible health concerns associated with power frequency EMFs which oscillate at 50 times per second in the UK and Europe and at 60 times per second in the USA and Canada.
As we are researching lower power frequency EMFs we need to consider the magnetic field and the electric field separately.
What are electric fields and magnetic fields?
Electric fields exist wherever there is a charged particle.
Magnetic fields are created whenever there is a flow of charged particles.
A wire with a voltage applied to it will produce an electric field even if there is no current flowing through it. The size of the electric field depends on the voltage. If a current flows through the wire, it will produce a magnetic field, the higher the current the greater the magnetic field. If the current stops flowing, the magnetic field disappears. This means that an appliance plugged into the mains will generate an electric field around it even if it is switched off. If it is then switched on it will also generate a magnetic field.
Both electric and magnetic fields are strongest close to their source and rapidly diminish with distance.
Electric fields are measured in Volts per metre, written V/m.
The unit of magnetic field strength is the Tesla (T), however one Tesla represents a fairly large magnetic field and so they are usually measured in microTeslas (µT)
* The term "EMF or EMFs" has two meanings depending on whether we are talking about power frequency or radio wave frequencies such as those used by mobile phones. At the frequencies used by the electricity supply (50 Hz, or cycles per second, in the UK) there is effectively no radiation involved, otherwise powerlines for example would act as an aerial and all of the electricity supply would be emitted into space! In fact at theses relatively low frequencies the electric and magnetic fields need to be described separately, hence at power frequencies the term EMFs means "electric and magnetic fields". In contrast however at mobile phone frequencies the electric and magnetic fields are intrinsically linked and radiation emitted as the so-called electromagnetic radiation. Thus, at mobile phone frequencies the term EMFs means Electromagnetic fields and the associated electromagnetic radiation.