physics//electromagnetism//electric field

An electric field is the influence an electric charge spreads through the space around it, telling any other charge placed there which way it will be pushed and how hard, and it is what an engineer designs against when spacing conductors, sizing insulation or keeping a spark from jumping. It is measured in volts per metre: the push per unit of charge.

An electric field is the influence an electric charge spreads through the space around it, telling any other charge placed there which way it will be pushed and how hard, and it is what an engineer designs against when spacing conductors, sizing insulation or keeping a spark from jumping. It is measured in volts per metre: the push per unit of charge.

The useful intuition is a slope. Between two points at different voltages, the field is roughly the voltage difference divided by the distance, so the same voltage across a shorter gap makes a stronger field. A 230 V socket gives a modest field across a centimetre of plastic; a few thousand volts on a hand a few millimetres from a doorknob gives a field strong enough to tear electrons off the air molecules in between.

A field needs no current. A charge sitting still sets up a field and nothing flows (set it moving and a magnetic field appears beside it, and a changing magnetic field makes an electric field in turn); an insulator placed in the field carries it without letting charge through, which is the principle of the capacitor.

Fields concentrate at sharp points. The field is strongest where the surface curves most, which is why sparks leave from points and edges and why high-voltage hardware has rounded ends.

Every material has a limit. Above a certain field the material stops insulating, dielectric breakdown: about 3 kV per millimetre for dry air, many times more for good plastics and ceramics.