ELECTRIC CURRENT GENERATION
The term "electric current" is used to mean electricity which flows through a conductor, a direct current being a cur. rent which flows in one direction only. There are four principal ways by which a direct current can be generated, viz.
1) chemical action;
2) thermal or heat action, the word thermal, coming from the Greek word "therme" which means "heat";
3) light action;
4) magnetic action.
To set up a current by chemical action, an alkali or an acid is used to react with a metal. Such an apparatus is called an electric cell, a group of two or more cells connected together forming a battery.
To produce a current by thermal action, heat is applied to two unlike metals soldered together in two places, the apparatus of this kind being called a thermoelectric couple or thermocouple, for short. We get the prefix "thermo" from "thermal", the origin of the last word having been mentioned above. The word "couple" in this term means that two unlike metals or metals and alloys are joined together so that they can be properly heated in the point of the joint.
The reason the thermocouple generates a current is due to the fact that the heat tears the electrons off of the negative inetal at the junction, just as the chemical action of an electric cell tears the electrons off of the zinc electrode. It is these electrons that form the current flowing through the circuit.
To develop a current by light action, light is made to fall on a special kind of a cell, the apparatus to be used in such a case being called a photoelectric cell.
Finally, in order to generate a current, a wire is made to cut, that is, to pass through a magnetic field, this latter being set up either by a permanent magnet or an electromagnet. Where the wire cuts through the magnetic field of a permanent magnet, the apparatus is called a magneto-electric machine or just "magneto", for short. The wire cutting through the magnetic field of an electromagnet, the apparatus is called a dynamo electric machine, or "dynamo", for short.
In general there are a number of ways by which electric currents can be generated by magnetic action, all of them being based on the same principle, that of cutting the magnetic lines of force with a conductor.
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1. The force of gravitational attraction exerted on a body by the earth known as the weight of the body is one of the most important forces in everyday life. 2. The total quantity of pure radium obtained is quite insignificant. 3. Intermolecular space exists even in a gas which, subjected to exceedingly high pressure ceases to contract its volume. 4. When used as an amplifier the radio-tube allows a small voltage to control a strong flow of current from a battery. 5. If a body is totally immersed in a fluid, the upthrust of the fluid on the body is equal to the weight of the fluid displaced. 6. When the water has reached the boiling point, the temperature ceases to rise, and the heat supplied is used in changing the water into steam. 7. A beaker filled with cold water and held over a flame of burning hydrogen will condense the steam to droplets of water. 8. Glass and porcelain neither lose nor gain in weight when heated. 9. Any open mass of water if left unreplenished will evaporate little by little. 10. The modern war is an all-round test of the material and spiritual strength of every nation involved. 11. Under ordinary pressure a given liquid boils at a fixed temperature. 12. Nitre gives off oxygen only when raised to a bright-red heat. 13. The efficiency of a machine is determined by the ratio of the useful work performed to the total work expended. 14. Radioisotopes produced by our atomic industry are widely used in medicine and agriculture. 15. Capacity is the property of two electrical conductors, when separated by insulation, to receive and retain electricity. 16. Fermentation used for producing alcohol from naturally occurring substances is one of the oldest processes known to man. 17. Alloys in general consist of two or more metals melted together and then allowed to solidify. 18. The properties of matter are better learned and understood when correlated with its structure in terms of molecules, atoms, and still smaller particles. 19. When ozone decomposes, the amount of energy liberated is equivalent to that absorbed in its formation. 20. Some liquids, and to a much smaller extent some solids, if placed in contact, tend to diffuse one into the other.
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1. The characteristics of the components so far considered can be presented by the following scheme. 2. The recent talks resulted in the agreement just signed. 3. The same encoded picture used to generate Fig. 8 was analysed using a balanced correlation procedure to produce Fig. 9. 4. Historical records show that a given region may undergo a spasm of activity followed by a lull of two or more centuries. 5. In this section we establish that, based on a stability assumption, these solutions exist and are unique in the mean absolute sense. 6. Based on a stage-by-stage schedule, the program embraces different fields of space research and exploration. 7. The data obtained outweighed those that we had had before. 8. At the end of the day, reports on all completed analyses can be provided, including the number of tests run that day, the amount of time required for those tests, and the number of samples completed. 9. As indicated, these similarities and differences will be explored in some detail. 10. Stated differently, the purpose of the present work is to explore the so far developed related theory and to stimulate attention on some connected still open questions. 11. The feasibility of this system depends on several related factors. 12. All things considered, the meeting may be declared closed.
