The ampere (A) is the SI unit of current and represents a flow of 6.24×1018 electrons per second past a fixed point.

In order for current to flow there must exist a potential difference between two points. This potential difference is similar to an electrical concentration gradient. It is the electromotive force which drives current flow and is measured in volts8. Each human tissue has its own inherent resistance to electrical flow. The relationship between current, voltage and resistance is summarised in Ohm’s law.

Ohm’s law:

V = IR

V = voltage, I = current, R = resistance

Flow of electricity results in the generation of heat. The relationship between current flow and energy or heat production is governed by Joule’s law.

Joule’s law:

R x I2 x time

The value for current is squared and as such it has the greatest influence on heat production associated with electrical injury. In many electrical injuries the current is often unknown. Voltage is used as a surrogate marker for the magnitude of current flow.