Safe ICT NZ
Safe Information and Communications Technology for New Zealand
Electric and magnetic fields
Chart courtesy of Argonne National Laboratory
Shared under Creative Commons licensing, You are free to share it for non-commercial use, you must attribute it.
"Electric and magnetic fields exist wherever electric current flows— in power lines and cables, residential wiring and electrical appliances.
Electric fields arise from electric charges, these are measured in volts per metre (V/m) and are shielded by common materials, such as wood and metal.
Magnetic fields arise from the motion of electric charges (i.e. a current), are expressed in tesla (T), or more commonly in millitesla (mT) or microtesla (µT). In some countries another unit called the gauss, (G), is commonly used (10,000 G = 1 T). These fields are not shielded by most common materials, and pass easily through them. Both types of fields are strongest close to the source and diminish with distance.
Most electric power operates at a frequency of 50 or 60 cycles per second, or hertz (Hz). Close to certain appliances, the magnetic field values can be of the order of a few hundred microtesla. Underneath power lines, magnetic fields can be about 20 µT and electric fields can be several thousand volts per metre.
However, average residential power-frequency magnetic fields in homes are much lower - about 0.07 µT in Europe and 0.11 µT in North America. Mean values of the electric field in the home are up to several tens of volts per metre." —WORLD HEALTH ORGANISATION
Electricity flow can be thought of something like a river:
Current:
Current is like the volume of electricity. This is measured in Amps.
A fine water jet:
This would be like a low amperage, high voltage supply
A slow-moving river:
This would be high amperage, low voltage.
Volts
The speed of the flow of power is the voltage, measures in Volts.r
would be high amperage, low voltage. You can drown in a slow moving river and a 12v car battery can easily kill you.
Watts
Watts is the voltage x amps, so it is equivalent if the volume per second.
Mains electricity: 240v in NZ is AC or alternating current. It switches between positive and negative. In NZ this is done 50 times a second, so 50 hertz.
"For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy."
Richard Feynman
— chapter 3, “The Great Conservation Principles,” p. 75