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

Page 28 text:

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.

Page 27 text:

THREE ELEMENT l'i1C7l7Zifll TVBE 23 the filament and the grid is positive all are drawn through the grid to the plate. fbi If under the same conditions the field is negative the emitted electrons are returned to the cathode. Ccj But when an alternating E. M. F. is impressed on the grid circuit so that the grid is alternately positive and negative in respect to the filament then the resistance of the input circuit will be variable for the positive half of the cycle and almost intinite for the negative half-cycle. NVhen the alternating current is superimposed on a constant nega- tive grid potential then the resistance of the grid circuit can be said to be intinite. The foregoing explanation contains implicitly the secret of the tube when functioning as a relay. Any variation of the grid potential changes the strength of the field between the filament and the grid causing a. like change in the num- ber of electrons passing from the filament to the plate. Po tential variations between the filament and grid occasion variations in the output circuit and, due to the impressed charge on the grid, the power developed in the output is greater than that expended in the input. Enterprising scientists have calculated that about two million billion electrons pass across the grid on their journey to the plate in an ordinary tube under ordinary conditions. The wires in the plate circuit carry approximately two million billion electrons per operating second while seventy million billion are emitted by the filament per burning second. Al- though the Vacuum Tube is exhausted to as nearly a perfect vacuum as man can get still it is known that there are re- maining in the tube perhaps four hundred and fifty billion molecules of air after the manufacturer has done all in his power to produce a perfect vacuum. Owing to the minute-- ness of these air particles, which have a radius of nearly ten billionths of an inch and there are so few of them Crelativclyj that, in a well made tube, the electrons, which constitute the space current infrequently, if ever, collide with them. It they do collide ionization by collision takes place which has

Page 29 text:

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.