St Ignatius College - Ignatian Yearbook (San Francisco, CA)

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JUNIOR LAW Hennessy, H. Brennan, W. Hammack. V Pittman, C. Devine, G. Labagh, S. Vinckler. A. O'Meara, E. O'B1'ien, T. Costello, D. Burke, G. Taddiucci, A.

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JUNIOR LAW Merrick, L. Deasy, C. Slevin, T. Cronin. J. Ortega, L. Glicksberg, A Neary, J. Donovan, D. Hughes, J. Healy. J. Riley. F. McCallion. N.

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26 THE IGNATIAN been already mentioned, This may take place with respect to residual air after evacuation or with molecules of a gas introduced after evacuation. The gas is sometimes required to produce special effects. The degree of ionization depends not only on the velocity with which the electron is moving when it strikes the gas molecule, but also on the pressure of the gas. If the gas pressure is very high it means that the molecules of the gas are very numerous and an electron may collide with one before it has attained speed sufficient to cause ionization. In this case ionization depends on the gas itself. If it consists of elastic particles then it is most probable that the electron will rebound and by so doing will gain sufficient velocity to ionize at the next collision. But if the gas is composed of hard inelastic particles then the elec- tron at the moment of impact may lose all its motion which it naturally imparts to the molecule it strikes. Energy thus imparted is radiated in the form of light, producing photo- electric effects. The HCharacteristic curveii of a tube is a plotted graph indicating the strength of the electron flow with various plate potential values. Theoretically it appears similar to a rather straight, figure S. Its curved ends are not very pronounced. The point along this curve where the tube functions best is called the critical pointf' This is not a constant but it changes with every individual tube and with the type of work being done. The critical point is usually situated on the lower half of the S just where the curve starts to straight- cn out. Ionization greatly intiuences the characteristic. The gas molecules, being split by bombardment, result in more dislodged charges so that the current may be increased. Re- sulting positive ions cause, by their presence in the negative space charge, a reduction of the charge and an increase in current passed. The life of the tube may be shortened under some conditions by the bombardment of the filament by posi- tive ions produced by collision. This causes an increase in temperature and saturation current and a consequent Wear-