Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points. The voltage between two points is equal to the work done per unit of charge against a static electric field to move a test charge between two points. This is measured in units of volts; moving 1 coulomb of charge across 1 volt of electric potential requires 1 joule of work. Voltage differences between points can be caused by static electric fields, by electric