Definition and General Concepts
– The SI unit of work per unit charge is the joule per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge).
– The voltage difference is denoted symbolically by ΔV, simplified especially in English-speaking countries.
– It is used in the context of Ohm’s or Kirchhoff’s circuit laws.
– The electrochemical potential is the voltage that can be directly measured with a voltmeter.
– Voltage is defined so that negatively charged objects are pulled towards higher voltages, while positively charged objects are pulled towards lower voltages.
– The electric potential can be generalized to electrodynamics, allowing for well-defined differences in electric potential between points.
– In electrodynamics, the electric field can no longer be expressed solely in terms of the electric potential.
– The potential is no longer uniquely determined and can take different forms based on the choice of gauge.
– Some authors use the word voltage to refer to the line integral of the electric field, rather than differences in electric potential.
– In this case, the voltage between two points depends on the path taken.
– Lumped element models are used in circuit analysis to represent and analyze circuits.
– Under the assumptions of a lumped element model, voltages between nodes in the circuit are well-defined.
– The electric field in the region exterior to each component is conservative.
– Voltages are calculated using the same formula as in electrostatics.
– Magnetic fields throughout the circuit can be modeled by adding mutual inductance elements.
The Volt
– The volt is the derived unit for electric potential, voltage, and electromotive force.
– The volt is named after the Italian physicist Alessandro Volta, who invented the voltaic pile.
– The volt is used to measure electric potential, voltage, and electromotive force.
– It is a fundamental unit in electrical engineering and physics.
– The volt is widely used in various applications, from household electricity to electronic devices.
Hydraulic Analogy
– The hydraulic analogy is a useful way to understand electrical concepts.
– In the analogy, an electric circuit is compared to water flowing in a closed circuit of pipework.
– The potential difference in an electric circuit corresponds to the pressure difference in the water circuit.
– Work can be done by an electric current driven by the potential difference, similar to water flowing and driving a turbine.
– The hydraulic analogy helps explain the relationship between voltage, current, and electrical power.
Measuring Voltage
– Specifying a voltage measurement requires explicit or implicit specification of the points across which the voltage is measured.
– When using a voltmeter to measure voltage, one electrical lead of the voltmeter must be connected to the first point, one to the second point.
– A common use of the term voltage is in describing the voltage dropped across an electrical device (such as a resistor).
– The voltage between two points is the sum of the voltage between the first point and a third point, and the voltage between the third point and the second point.
– The various voltages in a circuit can be computed using Kirchhoff’s circuit laws.
– Instantaneous voltages can be added for direct current (DC) and AC, but average voltages can be meaningfully added only when they apply to signals that all have the same frequency and phase.
– Instruments for measuring voltages include the voltmeter, the potentiometer, and the oscilloscope.
– Analog voltmeters work by measuring the current through a fixed resistor, which is proportional to the voltage 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 voltage and using it to deflect an electron beam from a straight path.
– The deflection of the beam is proportional to the voltage.
Typical Voltages
– A common voltage for flashlight batteries is 1.5 volts (DC).
– A common voltage for automobile batteries is 12 volts (DC).
– Common voltages supplied by power companies to consumers are 110 to 120 volts (AC) and 220 to 240 volts (AC).
– The voltage in electric power transmission lines used to distribute electricity from power stations can be several hundred times greater than consumer voltages, typically 110 to 1200 kV (AC).
– The voltage used in overhead lines to power railway locomotives is between 12 kV and 50 kV (AC) or between 0.75 kV and 3 kV (DC).
Galvani Potential vs. Electrochemical Potential
– Inside a conductive material, the energy of an electron is affected not only by the average electric potential but also by the specific thermal and atomic environment that it is in.
– When a voltmeter is connected between two different types of metal, it measures not the electrostatic potential difference, but instead something else that is affected by thermodynamics.
– The quantity measured by a voltmeter is the negative of the difference of the electrochemical potential of electrons divided by the electron charge and commonly referred to as the voltage difference.
– The pure unadjusted electrostatic potential is sometimes called Galvani potential.
– The terms voltage and electric potential are ambiguous and can refer to either of these in different contexts. Source: https://en.wikipedia.org/wiki/Electric_potential_difference
This article needs additional citations for verification. (February 2018) |
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to move a test charge between the two points. In the International System of Units (SI), the derived unit for voltage is the volt (V).
| Voltage | |
|---|---|
 Batteries are sources of voltage in many electric circuits. | |
Common symbols | V , ∆V , U , ∆U |
| SI unit | volt |
| In SI base units | kg⋅m2⋅s−3⋅A−1 |
Derivations from other quantities | Voltage = Energy / charge |
| Dimension | M L2 T−3 I−1 |
The voltage between points can be caused by the build-up of electric charge (e.g., a capacitor), and from an electromotive force (e.g., electromagnetic induction in a generator). On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect, and the thermoelectric effect. Since it is the difference in electric potential, it is a physical scalar quantity.
A voltmeter can be used to measure the voltage between two points in a system. Often a common reference potential such as the ground of the system is used as one of the points. A voltage can represent either a source of energy or the loss, dissipation, or storage of energy.
