Volt, definition

Ideally a standard cell is constmcted simply and is characterized by a high constancy of emf, a low temperature coefficient of emf, and an emf close to one volt. The Weston cell, which uses a standard cadmium sulfate electrolyte and electrodes of cadmium amalgam and a paste of mercury and mercurous sulfate, essentially meets these conditions. The voltage of the cell is 1.0183 V at 20°C. The a-c Josephson effect, which relates the frequency of a superconducting oscillator to the potential difference between two superconducting components, is used by NIST to maintain the unit of emf. The definition of the volt, however, remains as the Q/A derivation described. 

The most widely used reference electrode, due to its ease of preparation and constancy of potential, is the calomel electrode. A calomel half-cell is one in which mercury and calomel [mercury(I) chloride] are covered with potassium chloride solution of definite concentration this may be 0.1 M, 1M, or saturated. These electrodes are referred to as the decimolar, the molar and the saturated calomel electrode (S.C.E.) and have the potentials, relative to the standard hydrogen electrode at 25 °C, of 0.3358,0.2824 and 0.2444 volt. Of these electrodes the S.C.E. is most commonly used, largely because of the suppressive effect of saturated potassium chloride solution on liquid junction potentials. However, this electrode suffers from the drawback that its potential varies rapidly with alteration in temperature owing to changes in the solubility of potassium chloride, and restoration of a stable potential may be slow owing to the disturbance of the calomel-potassium chloride equilibrium. The potentials of the decimolar and molar electrodes are less affected by change in temperature and are to be preferred in cases where accurate values of electrode potentials are required. The electrode reaction is... 

Any surface (typically a piece of metal) on which an electrochemical reaction takes place will produce an electrochemical potential when in contact with an electrolyte (typically water containing dissolved ions). The unit of the electrochemical potential is volt (TV = 1JC1 s 1 in SI units).The metal, or strictly speaking the metal-electrolyte interface, is called an electrode and the electrochemical reaction taking place is called the electrode reaction. The electrochemical potential of a metal in a solution, or the electrode potential, cannot be determined absolutely. It is referred to as a potential relative to a fixed and known electrode potential set up by a reference electrode in the same electrolyte. In other words, an electrode potential is the potential of an electrode measured against a reference electrode. The standard hydrogen electrode (SHE) is universally adopted as the primary standard reference electrode with which all other electrodes are compared. By definition, the SHE potential is OV, i.e. the zero-point on the electrochemical potential scale. Electrode potentials may be more positive or more negative than the SHE. 

Einstein s hypothesis, then, led to two definite predictions. In the first place, there should be a photoelectric threshold frequencies less than a certain limit, equal to 4>/h, should be incapable of ejecting photoelectrons from a metal. This prediction proved to be verified experimentally, and with more and more accurate determinations of work function it continues to hold true. It is interesting to see where this threshold comes in the spectrum. For this purpose, it is more convenient to find the wave length X = c/v corresponding to the frequency /h. If we express in electron volts, as is commonly done, (see Eq. (1.1), Chap. IX), we have the relation... 

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

Volt — SI-derived measurement unit of the electric -> potential difference or voltage. Symbol V (named in honor of the Italian physicist Alessandro - Volta (1745— 1827)). Definition lvolt is the potential difference between two points of a homogeneous, linear conductor of constant temperature, when a current of one ampere converts one watt of power. 

No definite carbide of rhodium is known, although when heated in the electric furnace in contact with carbon, rhodium dissolves some of the last named, the amount varying according to circumstances, as much as 7-38 per cent, being absorbed in five minutes with a current of 910 amperes and 50 volts. The presence of carbon renders the metal less malleable. When heated in chlorine the carbon is deposited from the mixture as graphite.5... 

International Units.— The electrical units described in the previous section are defined in terms of quantities which cannot be easily established in the laboratory, and consequently an International Committee (1908) laid down alternative definitions of the practical units of electricity. The international ampere is defined as the quantity of electricity which flowing for one second will cause the deposition of 1.11800 milligrams of silver from a solution of a silver salt, while the international ohm is the resistance at 0 c. of a column of mercury 106.3 cm. long, of uniform cross-section, weighing 14.4521 g. The international volt is then the... 

Imagine a very dilute solution of an electrolyte, at a concentration c equiv. per liter, to be placed in a cube of 1 cm. side with square electrodes of 1 sq. cm. area at opposite faces, and suppose an e.m.f. of 1 volt to be applied. By definition, the specific conductance (ic) is the conductance of a centimeter cube, and the equivalent conductance of the given dilute solution, which is virtually that at infinite dilution, is 1000 k/c [see equation (5)], so that... 

---