Voltage

International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially known as high voltage symbol. The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements

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. In Physics, the potential difference or pd between two points is the difference of the points' Scalar potential, equivalent to the line integral An electronic circuit is a closed path formed by the interconnection of Electronic components through which an Electric current can flow The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. ^[1] It measures the potential energy of an electric field to cause an electric current in an electrical conductor. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. In Science and engineering, a conductor is a material which contains movable Electric charges. Depending on the difference of electrical potential it is called extra low voltage, low voltage, high voltage or extra high voltage. In Electricity supply, using extra-low voltage ( ELV) is one of several means to protect against Electrical shock. Low voltage is an Electrical engineering term that broadly identifies safety considerations of an Electricity supply system based on the Voltage used The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements Specifically Voltage is equal to energy per unit charge.

1 Explanation
2 Useful formulae
3 Measuring instruments
4 Safety
5 See also
6 References
7 External links

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. An electrical network is an interconnection of Electrical elements such as Resistors Inductors Capacitors Transmission lines Voltage At a point in space the electric potential is the Potential energy per unit of charge that is associated with a static (time-invariant Electric field This difference is directly proportional to the force that tends to push electrons or other charge-carriers from one point to the other. This article is about proportionality the mathematical relation The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J 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. Electromotive force ( emf, \mathcal{E} is a term used to characterize electrical devices such as Voltaic cells thermoelectric devices electrical

Voltage is a property of an electric field, not individual electrons. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can 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. A gravitational field is a model used within Physics to explain how gravity exists in the universe

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. A voltmeter is an instrument used for measuring the Electrical potential difference between two points in an electric circuit

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. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges 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. For other laws named after Gustav Kirchhoff, see Kirchhoff's laws.

When talking about alternating current (AC) there is a difference between instantaneous voltage and average voltage. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant 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. Direct current ( DC) is the unidirectional flow of Electric charge.

Hydraulic analogy

Main article: 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. The electronic&ndash hydraulic analogy (derisively referred to as the drain-pipe theory by Oliver Heaviside) is the most widely used analogy for "electron fluid" Gravitation is a natural Phenomenon by which objects with Mass attract one another Analogy is both the cognitive process of transferring Information from a particular subject (the analogue or source to another particular subject (the target and Fluid pressure is the Pressure at some point within a Fluid, such as water or air 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. A turbine is a rotary Engine that extracts Energy from a Fluid flow

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. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically 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. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. The potential difference between two points a and b is the line integral of the electric field E:

$V_a - V_b = \int _a ^b \mathbf{E}\cdot d\mathbf{l}.$

Useful formulae

DC circuits

$V = \sqrt{PR}$

$R = \frac{V}{I}$

where V = potential difference (volts), I = current intensity (amps), R = resistance (ohms), P = power (watts). In Mathematics, a line integral (sometimes called a path integral or curve integral) is an Integral where the function to be integrated

AC circuits

$V = \frac{P}{I\cos\phi}$

$V = \frac{\sqrt{PZ}}{\sqrt{\cos\phi}} \!\$

$V = \frac{IR}{\cos\phi}$

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

AC conversions

$V_{avg} = .637\,V_{pk} = \frac{2}{\pi} V_{pk} = \frac{\omega}{\pi}\int_0^{\pi/\omega} V_{pk} \sin(\omega t - k x) {\rm{d}}x \!\$

$V_{rms} = .707\,V_{pk} = \frac{1}{\sqrt{2}} V_{pk} = V_{pk} \sqrt{\langle \sin^2(\omega t - k x) \rangle} \!\$

$V_{pk} = 0.5\,V_{ppk} \!\$

$V_{avg} = .319\,V_{ppk}\!\$

$V_{rms} = .354\,V_{ppk} = \frac{1}{2 \sqrt{2}} V_{ppk}\!\$

$V_{avg} = 0.900\,V_{rms} = \frac{2 \sqrt{2}}{\pi} V_{rms}\!\$

Where V_pk=peak voltage, V_ppk=peak-to-peak voltage, V_avg=average voltage over a half-cycle, V_rms=effective (root mean square) voltage, and we assumed a sinusoidal wave of the form $V p k sin(ω t - k x)$ , with a period $T = 2π / ω$ , and where the angle brackets (in the root-mean-square equation) denote a time average over an entire period. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the

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

A multimeter set to measure voltage. A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic Measuring instrument that combines several

Instruments for measuring potential differences include the voltmeter, the potentiometer (measurement device), and the oscilloscope. A voltmeter is an instrument used for measuring the Electrical potential difference between two points in an electric circuit A potentiometer is a three-terminal Resistor with a sliding contact that forms an adjustable Voltage divider. An oscilloscope (commonly abbreviated to scope or O-scope) is a type of Electronic test equipment that allows signal Voltages to be viewed 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. Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the The potentiometer works by balancing the unknown voltage against a known voltage in a bridge circuit. A bridge circuit is a type of Electrical circuit in which the current in a conductor splits into two parallel paths and then recombines into a single conductor 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. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J

Safety

Electrical safety is discussed in the articles on High voltage (note that even low voltage, e. The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements g. of 50 Volts, can lead to a lethal electric shock) and Electric shock. "Electrocute" redirects here For the band see Electrocute (band.

References

^ "voltage", A Dictionary of Physics. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant Direct current ( DC) is the unidirectional flow of Electric charge. Mains is the general-purpose Alternating current (AC Electric power supply (as in "I've connected the appliance to the mains" This article includes a list of countries and territories with the plugs voltages and frequencies they use for providing electrical power to Small appliances Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the Voltage drop is the reduction in Voltage in an Electrical circuit between the source and load Ed. John Daintith. Oxford University Press, 2000. Oxford Reference Online. Oxford University Press.

External links

Elementary explanation of voltage at NDT Resource Center

Dictionary

-noun

(physics) the amount of electrostatic potential between two points in space.

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