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Encyclopedia > Voltage
International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially known as high voltage symbol.
International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially known as high voltage symbol.

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.[1] 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. Image File history File links High_voltage_warning. ... Image File history File links High_voltage_warning. ... In electrical engineering High voltage refers to a voltage which is high. ... Potential difference is a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. ... An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes. ... Josephson junction array chip developed by NIST as a standard volt. ... 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. ... This box:      Electric current is the flow (movement) of electric charge. ... In science and engineering, conductors, such as copper or aluminum, are materials with atoms having loosely held valence electrons. ... The use of extra low voltage (ELV) in an electrical circuit is one of several means to provide protection against electrical shock. ... low voltage ... In electrical engineering High voltage refers to a voltage which is high. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ...

Contents

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 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. An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... Electrical potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential or the electric potential, typically measured in volts. ... This article is about proportionality, the mathematical relation. ... For other uses, see Electron (disambiguation). ... Electromotive force (emf) is the amount of energy gained per unit charge that passes through a device in the opposite direction to the electric field existing across that device. ...


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. 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. ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... 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." The word ground has several meanings: The surface of the Earth Soil, a mixture of sand and organic material present on the surface of the Earth Ground (electricity), in electrical engineering, something that is connected to the Earth or at the voltage defined as zero (in the US, called ground...


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 digital voltmeters. ...


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. Magnetic field lines shown by iron filings Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box:      In physics, the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. ...


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. Not to be confused with Kerckhoffs principle. ...


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. City lights viewed in a motion blurred exposure. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...


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. 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. Since electric current is invisible and the processes at play in electronics are often difficult to understand in an intuitive way, it is common to teach electronics using analogies to more common sense objects and processes. ... Gravity is a force of attraction that acts between bodies that have mass. ... Analogy is both the cognitive process of transferring information from a particular subject (the analogue or source) to another particular subject (the target), and a linguistic expression corresponding to such a process. ... Fluid pressure is the pressure on an object submerged in a fluid, such as water. ... A Siemens steam turbine with the case opened. ...


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). This article is about pressure in the physical sciences. ... For other uses, see Volume (disambiguation). ...


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: This article is about the physical quantity. ... This box:      Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... This article is about path integrals in the general mathematical sense, and not the path integral formulation of physics which was studied by Richard Feynman. ...

V_a - V_b = int _a ^b mathbf{E}cdot dmathbf{l}.

Useful formulae

DC circuits

 V = sqrt{PR}
 V = frac{P}{I}
 R = frac{V}{I}

Where V=voltage/potential difference, I=current intensity, R=resistance, P=power/watts


AC circuits

 V = frac{P}{Icosphi}
 V = frac{sqrt{PZ}}{sqrt{cosphi}} !
 V = frac{IR}{cosphi}

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 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 Vpksin(ωtkx), 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 or rms is a statistical measure of the magnitude of a varying quantity. ...


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 set to measure voltage.

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 it. 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. Image File history File links Download high resolution version (672x800, 193 KB) Multimeter This image shows a digital multimeter. ... Image File history File links Download high resolution version (672x800, 193 KB) Multimeter This image shows a digital multimeter. ... A digital multimeter A low cost digital multimeter An analog benchtop multimeter A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. ... Two digital voltmeters. ... It has been suggested that Determining emf of primary cells using potentiometer be merged into this article or section. ... Illustration showing the interior of a cathode-ray tube for use in an oscilloscope. ... A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i. ... 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, thereby enclosing a loop. ... For other uses, see Electron (disambiguation). ...


Safety

Electrical safety is discussed in the articles on High voltage and Electric shock. In electrical engineering High voltage refers to a voltage which is high. ... Sign warning of possible electric shock hazard An electric shock can occur upon contact of a humans body with any source of voltage high enough to cause sufficient current flow through the muscles or hair. ...


See also

Electronics Portal

Image File history File links Nuvola_apps_ksim. ... City lights viewed in a motion blurred exposure. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Type F mains power plug & socket The term mains usually refers to the general purpose alternating current (AC) electrical power supply (as in “Ive connected the appliance to the mains”). The term is not usually used in the United States and Canada. ... // Plugs. ... A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i. ... This article or section does not cite its references or sources. ...

References

  1. ^ "voltage", A Dictionary of Physics. Ed. John Daintith. Oxford University Press, 2000. Oxford Reference Online. Oxford University Press.

External links

Look up Voltage in
Wiktionary, the free dictionary.

  Results from FactBites:
 
Virtual Laboratory: Voltage (675 words)
This measure of energy per unit charge is measured is called voltage (V) and the unit of measurement is called volts.
You are given a circuit on which you may vary the voltage by choosing from a variety of batteries and the resistance by adding resistors
To add batteries to the circuit, use the mouse to drag a battery from the toolbox (the box containing the various resistors and batteries) and drop it onto the larger battery on the circuit.
Voltage - Wikipedia, the free encyclopedia (674 words)
Voltage is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first chemical battery.
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.
Voltage is a property of an electric field, not individual electrons.
  More results at FactBites »

 
 

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