Potential difference

In physics, the potential difference is a quantity related to the amount of energy that would be required to move an object from one place to another against various types of forces. The term is most frequently used as an abbreviation of 'electrical potential difference', but it also occurs in many other branches of physics. Only changes in potential or potential energy (not the absolute values) can ever be measured.

Explanation
Potential difference is the difference in some quantity between two points in a conservative vector field of that quantity. Some examples are listed below.


 * In electrical engineering, electrical potential difference is the voltage present between two points, or the voltage drop transversely over an impedance (from one extremity to another). It is related to                                                                                                  the energy that would be required to move a unit of electrical charge from one point to the other against the electrostatic field that is present.  Unit: joules per coulomb = volt
 * 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. Unit: joules per kilogram.
 * In fluid systems the potential difference is the difference in pressure. Unit: pascals.
 * In thermal systems the potential difference is the difference in temperature. Unit: 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.