Electric fields can be present in any appliance plugged into a power point that is switched ‘on’. Even if the appliance is ‘off’ and the power point is ‘on’ an electric field will be present.
Electric fields are shielded by most objects, including trees, buildings and even human skin and their strength reduces rapidly as you move away from the source.
You may have seen people demonstrate how fluorescent tubes ‘light up’ when they are held under high voltage powerlines. A fluorescent tube works when an electric field inside the tube causes discharge, either as normal from the mains electricity supply or from an external electric field like that produced by a powerline.
The electric field created by the power line can cause a very small current to flow through the tube and this creates a weak glow. You can sometimes get the same effect in a dark room by holding one end of a fluorescent tube and rubbing your foot on a carpet to generate static electricity.
Magnetic fields are only present when electric ‘current’ is flowing. The strength of a magnetic field depends on the size of the current. Like electric fields, the strength of magnetic fields drops off quickly as you move away from the source.
While electric fields can be shielded, magnetic fields pass through most materials. As electric fields are naturally shielded, the electricity network generally contributes very little to the electrical fields measured inside a home or office building. For this reason most discussion on EMF usually focuses on magnetic fields