File Name: current and voltage measurement notes .zip
An electric circuit is formed when a conductive path is created to allow electric charge to continuously move. Voltage is a specific measure of potential energy that is always relative between two points. When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move charge carriers from one particular point in that circuit to another particular point.
Voltage , electric potential difference , electromotive force emf, electric pressure or electric tension is the difference in electric potential between two points, which in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units , the derived unit for voltage potential difference is named volt. The old SI definition for volt used power and current ; starting in , the quantum Hall and Josephson effect were used, and recently fundamental physical constants have been introduced for the definition of all SI units and derived units.
Voltage , electric potential difference , electromotive force emf, electric pressure or electric tension is the difference in electric potential between two points, which in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points.
In the International System of Units , the derived unit for voltage potential difference is named volt. The old SI definition for volt used power and current ; starting in , the quantum Hall and Josephson effect were used, and recently fundamental physical constants have been introduced for the definition of all SI units and derived units. Electric potential differences between points can be caused physically by electric charge build up or imbalance eg.
These latter processes at microscopic level have the physical origins previously mentioned. A voltmeter can be used to measure the voltage or potential difference 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 may represent either a source of energy electromotive force or lost, used, or stored energy potential drop.
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 this section.
Voltage is defined so that negatively charged objects are pulled towards higher voltages, while positively charged objects are pulled towards lower voltages. Therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. 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 " high tension " HT which is commonly used in thermionic valve vacuum tube based electronics.
In this case, the voltage increase from point A to point B is equal to the work 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 line integral of the electric field along that path.
Under this definition, the voltage difference between two points is not uniquely defined when there are time-varying magnetic fields since the electric force is not a conservative force in such cases. If this definition of voltage is used, any circuit where there are time-varying magnetic fields, [note 1] such as circuits containing inductors , will not have a well-defined voltage between nodes in the circuit. However, if magnetic fields are suitably contained to each component, then the electric field is conservative in the region exterior [note 2] to the components, and voltages are well-defined in that region.
Using the above definition, the electric potential is not defined whenever magnetic fields change with time. In physics, it is 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 electrodynamics :. The above decomposition is justified by Helmholtz's theorem. In this case, the voltage between points is always uniquely defined. In circuit analysis and electrical engineering , the voltage across an inductor is not considered to be zero or undefined, as the standard definition would suggest.
This is because electrical engineers use a lumped element model to represent and analyze circuits. 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. 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 toroid. If leaked fields are negligible, we find that.
The volt symbol: V is the derived unit for electric potential , electric potential difference, and electromotive force. The volt is named in honour of the Italian physicist Alessandro Volta — , who invented the voltaic pile , possibly the first chemical battery. A simple analogy for an electric circuit is water flowing in a closed circuit of pipework , driven by a mechanical pump. This can be called a "water circuit".
Potential difference between two points corresponds to the pressure difference between two points. If the pump creates a pressure difference between two points, then water flowing from one point to the other will be able to do work, such as driving a turbine.
Similarly, work can be done by an electric current driven by the potential difference provided by a battery. For example, the voltage provided by a sufficiently-charged automobile battery can "push" a large current through the windings of an automobile's starter motor. If the pump isn't working, it produces no pressure difference, and the turbine will not rotate.
Likewise, if the automobile's battery is very weak or "dead" or "flat" , then it will not turn the starter motor. The hydraulic analogy is a useful way of understanding many electrical concepts. In relation to "flow", the larger the "pressure difference" between two points potential difference or water pressure difference , the greater the flow between them electric current or water flow. See " electric power ".
Specifying a voltage measurement requires explicit or implicit specification of the points across which the voltage is measured. When using a voltmeter to measure potential difference, 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 drop across the device can be understood as the difference between measurements at each terminal of the device with respect to a common reference point or ground. The voltage drop is the difference between the two readings.
Two points in an electric circuit that are connected by an ideal conductor without resistance and not within a changing magnetic field have a voltage of zero. Any two points with the same potential may be connected by a conductor and no current will flow between them. 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 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 , such as moving-coil instruments, work by measuring the current through a fixed resistor, which, according to Ohm's Law , 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, so that the deflection of the beam is proportional to the voltage.
A common voltage for flashlight batteries is 1. 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 terms "voltage" and "electric potential" are ambiguous in that, in practice, they can refer to either of these in different contexts. The term electromotive force was first used by Volta in a letter to Giovanni Aldini in , and first appeared in a published paper in in Annales de chimie et de physique. However, a clear definition of voltage and method of measuring it had not been developed at this time. From Wikipedia, the free encyclopedia.
Difference in electric potential between two points in space. For other uses, see Voltage disambiguation. For other uses, see Potential. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. This article may be expanded with text translated from the corresponding article in Norwegian. May Click [show] for important translation instructions.
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For more guidance, see Wikipedia:Translation. Batteries are sources of voltage in many electric circuits. Derivations from other quantities. Electrical network. Covariant formulation. Electromagnetic tensor stress—energy tensor. Main article: Volt. Main article: Hydraulic analogy. Main articles: Galvani potential , Electrochemical potential , and Fermi level. Electronics portal. Alternating current AC Direct current DC Electric potential Electric shock Electrical measurements Electrochemical potential Fermi level High voltage Mains electricity an article about domestic power supply voltages Mains electricity by country list of countries with mains voltage and frequency Ohm's law Ohm Open-circuit voltage Phantom voltage.
Paris and F. Hammond, Electromagnetism for Engineers , p. II Ch. Retrieved 4 December Lang Fundamentals of electrochemistry. Varney, Leon H.
Brockman, "The origin of voltaic electricity: The contact vs. This means in AC circuits, there are always some non-confined magnetic fields. However, except at higher frequencies, these are neglected. If a component had an infinite extent, the region exterior to the components would not be simply connected, and thus integrals through it would still depend on the path taken.
This tutorial presents an introduction to Electrochemical Impedance Spectroscopy EIS theory and has been kept as free from mathematics and electrical theory as possible. If you still find the material presented here difficult to understand, don't stop reading. You will get useful information from this application note, even if you don't follow all of the discussions. No prior knowledge of electrical circuit theory or electrochemistry is assumed. Each topic starts out at a quite elementary level, then proceeds to cover more advanced material.
Instrument And Measurement Book Pdf. This value is also. Each operator measured the eight parts with the same instrument three times in a random order. The tool can be a single question, a questionnaire, a score obtained through physical examination, a laboratory measurement, a. Elements of generalized measurement system Module 2. Meter B is more sensitive d.
Not only can these be made to check the accuracy of a resistor, or check it is functioning correctly, but resistance measurements can be required in many other scenarios as well. It may be to measure the resistance of an unknown conductor, or it may be to check for short circuits and open circuits. In fact there are many instances where measuring resistance is of great interest and importance.
Premium Membership. Learn from experienced power engineers. Electrical voltage and current are two important quantities in an electrical network. The voltage is the effort variable without which no current is available.
Analogue multimeters have been in use for very many years and sometimes go by the name VOA as a result of the fact that they measure volts, ohms and amps. These multimeters are extremely flexible and enable very many faults to be found in an electronic circuit. Although analogue multimeters are now less common because digital multimeters, or DMMs are now more common, some analogue test meters are still available and may be found in some laboratories or may be available for use at home, etc. The analogue test meters are able to give a good account of themselves and can provide readings that are sufficiently accurate for most purposes. They do require a few different skills to the digital multimeters that are more widespread these days, but they are still very easy to use.
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