Current of electricity

The Berlin City electrical engineer M. Kallmann reported in 1899 on a system for controlling stray currents of electric railways [64]. As early as 1894, the Board of Trade in London issued a safety regulation for the British electric railways which specified a potential differential of not more than 1.5 V where the pipeline was positive to the rails, but 4.5 V with the rails positive. Extensive research was undertaken on reducing the risk of stray current in the soil by metallic connections from pipes to rails. However, as one writer noted, a procedure on these lines should definitely be discouraged as it carries the seed of its own destruction [64]. 

Electron-transfer reactions occur all around us. Objects made of iron become coated with mst when they are exposed to moist air. Animals obtain energy from the reaction of carbohydrates with oxygen to form carbon dioxide and water. Turning on a flashlight generates a current of electricity from a chemical reaction in the batteries. In an aluminum refinery, huge quantities of electricity drive the conversion of aluminum oxide into aluminum metal. These different chemical processes share one common feature Each is an oxidation-reduction reaction, commonly called a redox reaction, in which electrons are transferred from one chemical species to another. 

Of all electrical phenomena electrolysis appears the most likely to furnish us with a real insight into the true nature of the electric current, because we find currents of ordinary matter and currents of electricity forming essential parts of the same phenomenon. 

The production of a current of electricity by heating a junction formed by two dissimilar metals. For temperature measurement the metals are usually in the form of wires see Thermocouple) and the circuit has two junctions, the hot junction which is exposed to the temperature to be measured and the cold junction which is kept at a standard temperature. The thermo-electric effect is also termed the Seebeck Effect after its discoverer. 

In 1948 William Bradford Shockley (1910-1989), who is considered the inventor of the transistor, and his associates at Bell Research Laboratories, Walter Houser Brattain (1902-1987) and John Bardeen (1908-1991), discovered that a crystal of germanium could act as a semiconductor of electricity. This unique property of germanium indicated to them that it could be used as both a rectifier and an amplifier to replace the old glass vacuum tubes in radios. Their friend John Robinson Pierce (1910-2002) gave this new solid-state device the name transistor, since the device had to overcome some resistance when a current of electricity passed through it. Shockley, Brattain, and Bardeen all shared the 1956 Nobel Prize in Physics. 

Persulphates of potassium and ammonium are produced by passing a current of electricity through concentrated solutions of the sulphates in water. The persulphate is sparingly soluble, and deposits in white crystals. The formula appears to be M2S2Os (M = monad metal). The acid has bleaching powers, and gradually decomposes into sulphuric acid and ozone. 

The electrons flow along the copper rod and out through the wire attached to it so that a current of electricity flows through the tube. Such an X-ray tube emits X-rays with a long range of wave lengths, but it is found that no X-rays are produced with wave lengths shorter than a definite value. 

The importance of Volta s invention can scarcely be overestimated. For the first time, steady currents of electricity could be produced readily. 

A direct current of electricity passing along a coppei wire is a fiow of electrons along the wire. In a metal or similar conductor of electricity there are electrons which have considerable freedom of motion and which move along between the atoms of the metal when an electrical potential difference is applied. 

The phenomena that occur when a current of electricity is passed through such a solution are analogous to those described iif the preceding section for molten salt. The five steps are the following ... 

The reason that Equation 5 must be multiplied by 2 before it is added to Equation 6 is that when a current of electricity is conducted through the system the same number of electrons must pass from the cathode to the solution as from the solution to the anode Equation 5 as written above involves two electrons, and Equation 6 involves four hence Equation 5 must be doubled. 

It is not difficult to make calculations involving weights of chemical substances and the amount of electricity passing through an electrolytic cell, if you keep clearly in mind what the relation between the number of atoms and the number of electrons is. You must remember that the current of electricity, measured in amperes, is the rorte at which electricity is flowing through the cell. To find the amount of electricity the current must be multiplied by the time measured in seconds. One ampere flowing for one second is the quantity 1 coulomb of electricity. 

The factor i only occurs in solutions which are good conductors of electricity, and in 1887 Arrhenius succeeded in explaining these apparent deviations from the simple laws by his electrolytic dissociation theory. The molecules of an electrolyte are broken up to a greater or less extent into their free ions, even when the solution is not conducting a current of electricity. Thus we have the equation HCl H - - CL... 

By electrical we mean the phenomena of an induced current of electricity passing through a conductor and producing a useful effect in the form of heat or energy. An example of an electrical device would be the household iron. In this article, useful heat is produced by the passage of a current of electricity through a resistance unit imbedded within the iron itself. 

Wire of this variety is, in actuality, an electrical resistance. When a current of electricity is passed through a length of the wire, heat is produced. Most nichrome wire, like the more modern calrod typc units, will produce surface temperatures in excess of 1,000 degrees F. Nichrome wire may be purchased in almost any length desired or if secrecy is important, it may be removed from small heaters and toasters. It is also often found in the cheaper hot-plates, being embedded in a moulded refractory plate. 

Another similar appearing device will carry out the long distance phone call gambit but with a slightly different twist. If two electrical conductors are laid side by side, and if a current of electricity is passed through one of the conductors, a sympathetic or induced current is found to flow through the second or unconnected wire. In figure 46, induction is the source of our ultimate control impulse. 

The chemical power of a current of electricity exists in direct proportion to the absolute quantity of electricity that passes through it. 

The theory universally held at the present time is that conduction in metals is due to the movement of electrons. These arc the units of negative electricity, and have a mass of about 1/1S00 of that of the hydrogen ion, and a charge of 4.770 X 10 10 electrostatic units of electricity. A current of electricity in a metallic conductor is therefore due to a stream of electrons moving in the contrary direction to what is usually known as the "direction of the current/ More precisely, a galvanic current is due to superposing of a definite shift of the electrons in one direction on the random, or unordered, motion of the electrons in the metal. 

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