Electric fields are strongest close the device and diminish with distance. Common materials, such as wood and metal, shield against them. Magnetic fields arise from the motion of electric charges, i.e. a current . They govern the motion of moving charges. Any device connected to an electrical outlet, when the device is switched on and a current is flowing, will have an associated magnetic field that is proportional to the current drawn from the source to which it is connected.
Magnetic fields are strongest close to the device and diminish with distance.
They are not shielded by most common materials, and pass easily through them. Human exposure to ELF fields is primarily associated with the generation, transmission and use of electrical energy. Sources and typical upper limits of ELF fields found in the community, home and workplace are given below. Electrical energy from generating stations is distributed to communities via high voltage transmission lines. Transformers are used to lower the voltage for connections to residential distribution lines that deliver the energy to homes.