Potential difference

In physics, the potential difference or p.d. between two points is the amount of work that would need to be done on a unit electric charge to move it from one point to the other against an electric field. P.d. is synonymous with voltage and is measured in volts.

Theory
Potential difference is the line integral of the electric field strength between two points. Also, if v is the p.d. in volts, w is the work in joules (J), and q is the charge in coulombs (C), then:
 * $$ v = { w \over q } {\mathrm{J} \over \mathrm{C}} \ \mathrm{or} \ {w \over q} \mathrm{V} $$

In a more general sense, potential difference is the difference in some quantity between two points in a conservative vector field of that quantity.

Potential difference is therefore the amount of work needed to move one coulomb of electrons from one place to another.

Other types of potential difference
Other types of potential difference, related to the amount of energy required to move an object from one place to another against various types of forces, are also defined in physics.


 * In mechanics, the gravitational potential difference between two points on Earth is related to the energy that would be required to move a unit mass from one point to the other against the Earth's gravitational field. Units: joules per kilogram.
 * In fluid systems the potential difference is the difference in pressure. Units: pascals.
 * In thermal systems the potential difference is the difference in temperature. Units: kelvins.

In some engineering fields, "potential" is sometimes described as the 'across variable', whereas flux is the 'through variable'. The product of the flux and the potential difference is the power, which is the time rate of change of energy.