Magnetic fields

Magnetic fields are produced by current, which is the flow of electricity. Current, which is measured in amperes (amps) can be likened to the volume of water flowing in a hose when the nozzle is open. Generally, the higher the current, the higher the magnetic field.

Magnetic fields are usually measured in microteslas (µT) or nanoteslas (nT). One nanotesla is one thousandth of a microtesla . more on units

The Earth's natural magnetic field is approximately 50 µT in the UK.

Anything which uses or carries mains electricity is potentially a source of power-frequency magnetic fields, which modulate the Earth's steady natural fields. The strength of the magnetic-field modulation depends on the current (often referred to as the load) carried by the equipment. In the case of a power line, this varies according to the demand for power at any given time.

Magnetic fields are little affected by trees, hedges, fences, and ordinary building materials – unlike electric fields. More on screening fields.

Iron Filings used to highlight the magnetic field lines produced by a 1000 A current.

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