Units electric current

Electrolytic Preparation of Chlorine and Caustic Soda. The preparation of chlorine [7782-50-5] and caustic soda [1310-73-2] is an important use for mercury metal. Since 1989, chlor—alkali production has been responsible for the largest use for mercury in the United States. In this process, mercury is used as a flowing cathode in an electrolytic cell into which a sodium chloride [7647-14-5] solution (brine) is introduced. This brine is then subjected to an electric current, and the aqueous solution of sodium chloride flows between the anode and the mercury, releasing chlorine gas at the anode. The sodium ions form an amalgam with the mercury cathode. Water is added to the amalgam to remove the sodium [7440-23-5] forming hydrogen [1333-74-0] and sodium hydroxide and relatively pure mercury metal, which is recycled into the cell (see Alkali and chlorine products). 

E = dV/dx defined as V/m. The ions and electrons reestablish equilibrium by moving in the field which results in a net electric current density j defined as C/(m -s) or A/m. An electron or an electron hole has a unit charge, e = 1.601 x 10 C an ion has this unit charge times its valence Thus the... 

In the simplest case of one-dimensional steady flow in the x direction, there is a parallel between Eourier s law for heat flowrate and Ohm s law for charge flowrate (i.e., electrical current). Eor three-dimensional steady-state, potential and temperature distributions are both governed by Laplace s equation. The right-hand terms in Poisson s equation are (.Qy/e) = (volumetric charge density/permittivity) and (Qp // ) = (volumetric heat generation rate/thermal conductivity). The respective units of these terms are (V m ) and (K m ). Representations of isopotential and isothermal surfaces are known respectively as potential or temperature fields. Lines of constant potential gradient ( electric field lines ) normal to isopotential surfaces are similar to lines of constant temperature gradient ( lines of flow ) normal to... 

The term resistance refers to the property of any object or substance to resist or oppose the flow of an electrical current. The unit of resistance is the ohm. The abbreviation for electric resistance is R and the symbol for ohms is the Greek letter omega, Q. For certain electrical calculations the reciprocal of resistance is used, 1/R, which is termed conductance, G. The unit of conductance is the mho, or ohm spelled backward, and the symbol is an inverted omega. 

It is usual these days to express all physical quantities in the system of units referred to as the Systeme International, SI for short. The International Unions of Pure and Applied Physics, and of Pure and Applied Chemistry both recommend SI units. The units are based on the metre, kilogram, second and the ampere as the fundamental units of length, mass, time and electric current. (There are three other fundamental units in SI, the kelvin, mole and candela which are the units of thermodynamic temperature, amount of substance and luminous intensity, respectively.)... 

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 ... 

An important property of this or any electrical circuit is the rate that charge moves past a place in the circuit (e.g., out from or into a battery terminal). The electrical current (I) is defined to be the charge (Q) that flows, divided by the time (t) required for the flow I = Q/t. In S.I. units the current (I) is in amperes (A). 

The photoelectric effect (the creation of an electrical current when light shines on a photosensitive material connected m an electrical circuit) was first obseiwed in 1839 by the French scientist Edward Becqiierel. More than one hundred years went by before researchers in the United States Bell Laboratories developed the first modern PV cell in 1954. Four years later, PV was used to power a satellite in space and has provided reliable electric power for space exploration ever since. 

For one minute, one horsepower will lift 33,000 pounds one foot, or as a unit of power, this equals a rate of 33,000 foot-pounds of work per minute, or 550 foot-pounds per second. One horsepower equals 746 watts of power. The resistance to flow of electrical current through a wire or conductor is termed an ohm. One ohm is the amount of resistance in a wire through which one ampere of current flows under one volt of electrical pressure. Useful relationships are ... 

Analogies exist between electric and magnetic fields. The magnetic flux (4>) is analogous to electric current and has SI units of webers (see Table 2-36). The magnetic... 

Current (/) the rate of transfer of electric charge unit current is the ampere (A) which is the transfer of 1 coulomb/second (1 C/s). 

Let us now consider the situation when this balance has been upset by the presence of a weak electric field perpendicular to AB. The motion of the ions will no longer be completely random, but a tendency to drift will be superimposed on the random motion. If in unit time there has been an appreciable excess flow of negative ions across AB in one direction, we can be certain that there has been an appreciable excess flow of positive ions across AB in the opposite direction. These two separate contributions will together constitute the electric current. 

The coulomb is a unit of electric charge. Its magnitude can be appraised by its relation to the ampere. One ampere is an electric current of one coulomb of charge passing a point in a wire every second. One mole of electrons has, then, 96,500 coulombs of charge. In a wire carrying 10 amperes, it takes about two and one half hours for one mole of electrons to pass any point. 

Electric current, 78 Electric dipoles, see Dipoles Electric discharge, 239 Electric force, 76, 77 Electricity, fundamental unit, 241 Electrochemical cell chemistry of, 199 and Le Chatelier s Principle. 214 operation, 206 standard half cell, 21C Electrodes, 207 Electrolysis, 220, 221 apparatus, 40 cells, 238 of water, 40, 115 Electrolytes, 169, 179 strong, 180 weak,180... 

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. 

In this book, we will express our thermodynamic quantities in SI units as much as possible. Thus, length will be expressed in meters (m), mass in kilograms (kg), time in seconds (s), temperature in Kelvins (K), electric current in amperes (A), amount in moles (mol), and luminous intensity in candella (cd). Related units are cubic meters (m3) for volume, Pascals (Pa) for pressure. Joules (J) for energy, and Newtons (N) for force. The gas constant R in SI units has the value of 8.314510 J K l - mol-1, and this is the value we will use almost exclusively in our calculations. 

Electrical current (I) has been chosen as the basic SI unit in terms of which all other electrical quantities are defined. Unit current, the ampere (A, or amp), is defined in terms of the force exerted between two parallel conductors in which a current of 1 amp is flowing. Since the unit of power, the watt, is the product of current and potential difference,... 

Figure 25. Movement rate of bilayer devices (along an angle of 90°) with different dimensions (different polypyrrole weights) versus applied electrical current per mass unit (mA mg ). (Reprinted fromT. F. Otero and J. M. Sansinana, Bilayerdimensions and movement of artificial muscles. Bioelectrochem. Bioener-genetics 47, 117, 1997, Fig. 4. Copyright 1997. Reprinted with permission from Elsevier Science.)...

International System (SI) in terms of which all other units are defined. Examples kilogram for mass meter for length second for time kelvin for temperature ampere for electric current, basic ion An ion that acts as a Bronsted base. 

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 ... 

Here, / is the electric field, k is the electrical conductivity or electrolytic conductivity in the Systeme International (SI) unit, X the thermal conductivity, and D the diffusion coefficient. is the electric current per unit area, J, is the heat flow per unit area per unit time, and Ji is the flow of component i in units of mass, or mole, per unit area per unit time. 

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). 

It is well to remember that in the past, the unit of electrical current—the international ampere—was defined as the strength of an invariant current which, when sent throngh a silver nitrate solution, would deposit l.lllSOOmg silver at the cathode. Today, another definition of the ampere as an SI unit is valid. 

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