Electric current, unit measurement

Ampere The unit of measure of electric current. Electric current is measured by the number of electrons that flow past a given point in a circuit in 1 s. 

Electrical conductivity is an index of a material s ability to conduct an electric current. The electric current occurs in a conductor when an electrical potential difference is placed across it. The strength of electric current I measured (unit amperes. A) depends on the conductor material, on the electrostatic... 

The most fundamental quantity used in the study of electricity is electrical current (7). Electrical current is measured in one of the base units of the International System, the ampere (A). There are two types of electrical current direct current (dc), in which the current flows in only one direction, and alternating current (ac), in which the current flows alternately in opposite directions. 

The quantity of electric charge is measured m coulombs, and the unit of electric current—the number of coulombs per second that go past any point— is the ampere (A), named after French physicist Andre Marie Ampere ... 

The phenomenon of transmitting electrons through a body (an electric current). Usually associated with the measurement of electrical conductivity through water and measured in micro Siemens per centimeter (p,S/cm) or micromho per centimeter ( xmho/cm). 1 p,S/cm = 1 xmho/cm. The mho is equivalent to a reciprocal ohm (the unit of resistivity). 

A measure of ability of water to conduct an electric current and often related to TDS content of water. Typically, one pS/cm units of conductivity x 0.65 equals ppm TDS. 

Electricity is normally measured in units of charge, the coulomb (C), or as rate of electrical current flow, the ampere (A 1 A — 1 C/. ). The total amount of charge is the product of the current flow, symbolized by I, and the time for which this current flows Charge = It Just as molar mass provides the link between mass and moles, the Faraday constant provides the link between charge and moles. The number of moles of electrons transferred in a specific amount of time is the charge in coulombs divided by the charge per mole, F ... 

Conductivity is a very important parameter for any conductor. It is intimately related to other physical properties of the conductor, such as thermal conductivity (in the case of metals) and viscosity (in the case of liquid solutions). The strength of the electric current I in conductors is measured in amperes, and depends on the conductor, on the electrostatic field strengtfi E in tfie conductor, and on the conductor s cross section S perpendicular to the direction of current flow. As a convenient parameter that is independent of conductor dimensions, the current density is used, which is the fraction of current associated with the unit area of the conductor s cross section i = I/S (units A/cnF). 

If no side reactions occur at the electrode that would participate in the overall current flow, then the Faraday law can be used not only to measure the charge passed (i.e. in coulometres see Section 5.5.4) but also to define the units of electric current and even to determine Avogadro s constant. 

Scientists measure many different quantities—length, volume, mass (weight), electric current, temperature, pressure, force, magnetic field intensity, radioactivity, and many others. The metric system and its recent extension, Systeme International d Unites (SI), were devised to make measurements and calculations as simple as possible. In this chapter, length, area, volume, and mass will be introduced. Temperature will be introduced in Sec. 2.7 and used extensively in Chap. 11. The quantities to be discussed here are presented in Table 2-1. Their units, abbreviations of the quantities and units, and the legal standards for the quantities are also included. 

Both ion and electron transfer reactions entail the transfer of charge through the interface, which can be measured as the electric current. If only one charge transfer reaction takes place in the system, its rate is directly proportional to the current density, i.e. the current per unit area. This makes it possible to measure the rates of electrochemical reactions with greater ease and precision than the rates of chemical reactions occurring in the bulk of a phase. On the other hand, electrochemical reactions are usually quite sensitive to the state of the electrode surface. Impurities have an unfortunate tendency to aggregate at the interface. Therefore electrochemical studies require extremely pure system components. 

Electrochemical interfaces are sometimes referred to as electrified interfaces, meaning that potential differences, charge densities, dipole moments, and electric currents occur. It is obviously important to have a precise definition of the electrostatic potential of a phase. There are two different concepts. The outer or Volta potential ij)a of the phase a is the work required to bring a unit point charge from infinity to a point just outside the surface of the phase. By just outside we mean a position very close to the surface, but so fax away that the image interaction with the phase can be ignored in practice, that means a distance of about 10 5 — 10 3 cm from the surface. Obviously, the outer potential i/ a U a measurable quantity. 

As a first step, you need information about measurements in electricity. You know that the flow of electrons through an external circuit is called the electric current. It is measured in a unit called the ampere (symbol A), named after the French physicist Andre Ampere (1775-1836). The quantity of electricity, also known as the electric charge, is the product of the current flowing through a circuit and the time for which it flows. The quantity of electricity is measured in a unit called the coulomb (symbol C). This unit is named after another French physicist, Charles Coulomb (1736-1806). The ampere and the coulomb are related, in that one coulomb is the quantity of electricity that flows through a circuit in one second if the current is one ampere. This relationship can be written mathematically. 

Fignre 3.12 shows the operational scheme of a photoconduction detector. The incident light creates an electrical current and this is measured by a voltage signal, which is proportional to the light intensity. This proportional relation is provided by the fact that, in most photoconduction detectors, the density of carriers in the steady state is proportional to the number of absorbed photons per unit of time that is, proportional to the incident power. 

SI units of measurement, used by scientists around the world, derive their name from the French Systeme International d Unites. Fundamental units (base units) from which all others are derived are defined in Table 1-1. Standards of length, mass, and time are the meter (m). kilogram (kg), and second (s), respectively. Temperature is measured in kelvins (K), amount of substance in moles (mol), and electric current in amperes (A). 

I is electric current, measured in amperes (A). It is coulombs per second moving past a point in the circuit. R is resistance in ohms (ft). Units A = V/il. 

Resistivity, p, measures how well a substance retards the flow of electric current when an electric field is applied J = Elp, where J is current density (current flowing through a unit cross section of the material, A/m2) and E is electric field (V/m). Units of resistivity are V m/A or fl m, because... 

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