Volt-coulomb, definition

Let us call to mind the analogy between the flow of electricity along a wire and the flow of water in a pipe. Quantity of water is measured in liters or cubic feet quantity of electricity is usually measured in coulombs (ampere seconds). Rate of flow, or current, of water, the quantity passing a given point of the pipe in unit time, is measured in liters per second, or cubic feet per second current of electricity is measured in amperes (coulombs per second). The rate of flow of water in a pipe depends on the difference in the pressures at the two ends of the pipe, with atmospheres or pounds per square inch as units. The current of electricity in a wire depends on the electric potential difference or voltage drop between its ends, which is usually measured in volts. The definitions of the unit of quantity of electricity (the coulomb) and the unit of electric potential (the volt) have been made by international agreement. 

Definition A condenser has the capacitance of 1 farad, when a charge of 1 - coulomb generates a voltage of 1 volt. 

Volt The potential at a point in an electrostatic field is 1 volt, if 1 Joule of work per coulomb is done against electrical forces when a charge is brought from infinity to a point. A more usable definition is that / volt = / ampere flowing through a resistance of 1 ohm. E = 1 x R. Voltages are measured with voltmeters. 

How are the units of cell potential related to those of energy available to do work As you ve seen, work is done when charge moves between electrode compartments that differ in electrical potential. The SI unit of electrical potential is the volt (V), and the SI unit of electrical charge is the coulomb (C). By definition, for two electrodes that differ by 1 volt of electrical potential, 1 joule of energy is released (that is, 1 joule of work can be done) for each coulomb of charge that moves between the electrodes. Thus,... 

The higher the value of /, the smaller the value of A. Here is Faraday s constant, R is the universal gtis constant, T is the absolute temperature and e is the electrical permittivity of the fluid. This quantity e is the product of the relative dielectric constant of the medium (for water = 78.54 at 25 °C) and the electrical permittivity So of vacuum (= 8.8542 x 10 farad/cm or coulomb/volt-cm = 8.854 x 10 cou-lomh /newton-m, where recall that 1 newton-m = 1 volt-coulomh = 1 joule). In a uni-univalent electrolyte solution of 0.1 M strength (of, say, NaCl) the value of A at 25 °C is 9.6 X 10 cm, i.e. 0.96 nm (Newman, 1973). The ions of opposite charge shield the charge of the ion of interest, and the effect of the ion of interest decays very rapidly with distance. So the description of the electrical force on an ion in an applied field E by definition (3.1.8) is generally satisfactory. 

By definition, a capacitor has a capacitance (C) of one farad (symbol F) when a p.d. of one volt maintains a charge of one coulomb on that capacitor. 

The capacitance C is defined as the charge stored divided by the voltage applied, or C = Q/V. The unit of capacitance is the farad (from Michael Faraday) which, by definition, is 1 Coulomb/V. The stored charge is equal to the product of the area A, the electric field, and the dielectric constant of the material between the plates, or Q = sEA. From this relationship, we see that the permittivity s must have the units of Coulombs/Volt-m or Coulombs /Nt-m. Since the electric displacement D = sE, we see that D is the charge displaced per area, or the surface charge on the capacitor. The electric field is the potential V divided by the distance d between the plates or E = V/d. Therefore, C = sAId. 

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