# Dictionary Definition

voltage

### Noun

1 the rate at which energy is drawn from a source
that produces a flow of electricity in a circuit; expressed in
volts [syn: electromotive
force, emf]

2 the difference in electrical charge between two
points in a circuit expressed in volts [syn: electric
potential, potential, potential
difference, potential
drop]

# User Contributed Dictionary

#### Translations

amount of electrostatic potential

# Extensive Definition

Voltage (sometimes also called electric or
electrical tension) is the difference
of electrical potential between two points of an electrical or
electronic
circuit, expressed in volts. It measures the potential
energy of an electric
field to cause an electric
current in an electrical
conductor. Depending on the difference of electrical potential
it is called extra low
voltage, low voltage,
high
voltage or extra
high voltage. Specifically Voltage is equal to energy per unit
charge.

## Explanation

Between two points in an electric field, such as exists in an electrical circuit, the difference in their electrical potentials is known as the electrical potential difference. This difference is directly proportional to the force that tends to push electrons or other charge-carriers from one point to the other. Electrical potential difference can be thought of as the ability to move electrical charge through a resistance. At a time in physics when the word force was used loosely, the potential difference was named the electromotive force or EMF—a term which is still used in certain contexts.Voltage is a property of an electric
field, not individual electrons. An electron moving across a
voltage difference experiences a net change in energy, often
measured in electron-volts.
This effect is analogous to a mass falling through a given height
difference in a gravitational
field.

When using the term 'potential difference' or
voltage, one must be clear about the two points between which the
voltage is specified or measured. There are two ways in which the
term is used. This can lead to some confusion.

### Voltage with respect to a common point

One way in which the term voltage is used is when specifying the voltage of a point in a circuit. When this is done, it is understood that the voltage is usually being specified or measured with respect to a stable and unchanging point in the circuit that is known as ground or common. This voltage is really a voltage difference, one of the two points being the reference point, which is ground. A voltage can be positive or negative. "High" or "low" voltage may refer to the magnitude (the absolute value relative to the reference point). Thus, a large negative voltage may be referred to as a high voltage. Other authors may refer to a voltage that is more negative as being "lower".### Voltage between two stated points

Another usage of the term "voltage" is in
specifying how many volts are across an electrical device (such as
a resistor). In this case, the "voltage," or, more accurately, the
"voltage across the device," is really the first voltage taken,
relative to ground, on one terminal of the device minus a second
voltage taken, relative to ground, on the other terminal of the
device. In practice, the voltage across a device can be measured
directly and safely using a voltmeter that is isolated
from ground, provided that the maximum voltage capability of the
voltmeter is not exceeded.

Two points in an electric circuit that are
connected by an "ideal conductor," that is, a conductor without
resistance and not within a changing magnetic
field, have a potential difference of zero. However, other
pairs of points may also have a potential difference of zero. If
two such points are connected with a conductor, no current will
flow through the connection.

### Addition of voltages

Voltage is additive in the following sense: the voltage between A and C is the sum of the voltage between A and B and the voltage between B and C. The various voltages in a circuit can be computed using Kirchhoff's circuit laws.When talking about alternating
current (AC) there is a difference between instantaneous
voltage and average voltage. Instantaneous voltages can be added as
for direct
current (DC), but average voltages can be meaningfully added
only when they apply to signals that all have the same frequency
and phase.

### Hydraulic analogy

If one imagines water circulating in a network of pipes, driven by pumps in the absence of gravity, as an analogy of an electrical circuit, then the potential difference corresponds to the fluid pressure difference between two points. If there is a pressure difference between two points, then water flowing from the first point to the second will be able to do work, such as driving a turbine.This hydraulic analogy is a useful method of
teaching a range of electrical concepts. In a hydraulic system, the
work done to move water is equal to the pressure multiplied by the
volume of water moved.
Similarly, in an electrical circuit, the work done to move
electrons or other charge-carriers is equal to 'electrical
pressure' (an old term for voltage) multiplied by the quantity of
electrical charge moved. Voltage is a convenient way of quantifying
the ability to do work. In relation to electric current, the larger
the gradient (voltage or hydraulic) the greater the current
(assuming resistance is constant).

### Mathematical definition

The electrical potential difference is defined as the amount of work needed to move a unit electric charge from the second point to the first, or equivalently, the amount of work that a unit charge flowing from the first point to the second can perform. The potential difference between two points a and b is the line integral of the electric field E:- V_a - V_b = \int _a ^b \mathbf\cdot d\mathbf.

## Useful formulae

### DC circuits

- V = \sqrt

- R = \frac

where V = potential difference (volts), I =
current intensity (amps), R = resistance (ohms), P = power
(watts).

### AC circuits

- V = \frac

- V = \frac \!\

- V = \frac

Where V=voltage, I=current, R=resistance, P=true
power, Z=impedance, φ=phasor angle between I and V

### AC conversions

- V_ = .637\,V_ = \frac V_ = \frac\int_0^ V_ \sin(\omega t - k x) x \!\

- V_ = .707\,V_ = \frac V_ = V_ \sqrt \!\

- V_ = 0.5\,V_ \!\

- V_ = .319\,V_\!\

- V_ = .354\,V_ = \frac V_\!\

- V_ = 0.900\,V_ = \frac V_\!\

Where Vpk=peak voltage, Vppk=peak-to-peak
voltage, Vavg=average voltage over a half-cycle, Vrms=effective
(root mean
square) voltage, and we assumed a sinusoidal wave of the form
V_ \sin(\omega t - k x) , with a period T = 2\pi/\omega , and where
the angle brackets (in the root-mean-square equation) denote a time
average over an entire period.

### Total voltage

Voltage sources and drops in series:

- V_T = V_1 + V_2 + V_3 + ... + V_n \!\

Voltage sources and drops in parallel:

- V_T = V_1 = V_2 = V_3 = ... = V_n \!\

Where n \!\ is the nth voltage source or
drop

### Voltage drops

Across a resistor (Resistor R):

- V_R = IR_R \!\

Across a capacitor (Capacitor C):

- V_C = IX_C \!\

Across an inductor (Inductor L):

- V_L = IX_L \!\

Where V=voltage, I=current, R=resistance,
X=reactance.

## Measuring instruments

Instruments for measuring potential differences include the voltmeter, the potentiometer (measurement device), and the oscilloscope. The voltmeter works by measuring the current through a fixed resistor, which, according to Ohm's Law, is proportional to the potential difference across the resistor. The potentiometer works by balancing the unknown voltage against a known voltage in a bridge circuit. The cathode-ray oscilloscope works by amplifying the potential difference and using it to deflect an electron beam from a straight path, so that the deflection of the beam is proportional to the potential difference.## Safety

Electrical safety is discussed in the articles on High voltage (note that even low voltage, e. g. of 50 Volts, can lead to a lethal electric shock) and Electric shock.## See also

- Alternating current (AC)
- Direct current (DC)
- Mains electricity (an article about domestic power supply voltages)
- Mains power systems (List of voltage by country)
- Ohm's law
- Voltage drop

## References

## External links

voltage in Arabic: فرق الكمون

voltage in Bulgarian: Електрическо
напрежение

voltage in Catalan: Diferència de
potencial

voltage in Czech: Elektrické napětí

voltage in Danish: Elektrisk spænding

voltage in German: Elektrische Spannung

voltage in Estonian: Pinge (elekter)

voltage in Modern Greek (1453-): Διαφορά
δυναμικού

voltage in Spanish: Tensión (electricidad)

voltage in Esperanto: Elektra tensio

voltage in French: Tension électrique

voltage in Korean: 전압

voltage in Croatian: Napon

voltage in Indonesian: Tegangan listrik

voltage in Italian: Tensione elettrica

voltage in Hebrew: מתח חשמלי

voltage in Latin: Tensio electrica

voltage in Latvian: Spriegums

voltage in Lithuanian: Elektrinė įtampa

voltage in Dutch: Elektrische spanning

voltage in Japanese: 電圧

voltage in Norwegian: Elektrisk spenning

voltage in Norwegian Nynorsk: Elektrisk
spenning

voltage in Polish: Napięcie elektryczne

voltage in Portuguese: Tensão elétrica

voltage in Romanian: Tensiune electrică

voltage in Quechua: Pinchikilla mast'ay

voltage in Russian: Электрическое
напряжение

voltage in Simple English: Voltage

voltage in Slovenian: Električna napetost

voltage in Serbian: Електрични напон

voltage in Finnish: Jännite

voltage in Swedish: Elektrisk spänning

voltage in Tamil: மின்னழுத்தம்

voltage in Thai: ความต่างศักย์

voltage in Turkish: Gerilim (elektrik)

voltage in Ukrainian: Напруга

voltage in Chinese: 電壓

voltage in Slovak: Elektrické
napätie