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|V , ∆V , U , ∆U|
|Voltage = |
|M L2 T−3 I−1|
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Voltage, electric potential difference, electric pressure or electric tension is the difference in
Electric potential differences between points can be caused by electric charge, by
There are multiple useful ways to define voltage, including the standard definition mentioned at the start of this page. There are also other useful definitions of work per charge (see
Roughly speaking, voltage is defined so that negatively charged objects are pulled towards higher voltages, while positively charged objects are pulled towards lower voltages. Therefore, the
Historically, voltage has been referred to using terms like "tension" and "pressure". Even today, the term "tension" is still used, for example within the phrase "
The voltage increase from some point to some point is given by
In this case, the voltage increase from point A to point B is equal to the work which would have to be done per unit charge, against the electric field, to move the charge from A to B without causing any acceleration. Mathematically, this is expressed as the
If this definition of voltage is used, any circuit where there are time-varying magnetic fields[note 1], such as circuits containing
despite the fact that, internally, the electric field in the coil is zero (assuming it is a perfect conductor).
Using the above definition, the electric potential is not defined whenever magnetic fields change with time. In physics, it's sometimes useful to generalize the electric potential by only considering the conservative part of the electric field. This is done by the following decomposition used in
In this case, the voltage increase from to is given by
where is the rotational electric field due to time-varying magnetic fields. In this case, the voltage between points is always uniquely defined.
When using a lumped element model, it is assumed that there are no magnetic fields in the region surrounding the circuit and that the effects of these are contained in 'lumped elements', which are idealized and self-contained circuit elements used to model physical components. If the assumption of negligible leaked fields is too inaccurate, their effects can be modelled by
In the case of a physical inductor though, the ideal lumped representation is often accurate. This is because the leaked fields of the inductor are generally negligible, especially if the inductor is a
is path-independent, and there is a well-defined voltage across the inductor's terminals. This is the reason that measurements with a voltmeter across an inductor are often reasonably independent of the placement of the test leads.