. The thermionic vacuum tube and its applications . ectrons strike the emitting electrode, be increased to asufficiently high value one primary electron can expel as many astwenty secondary electrons. »H. Dember, Verb. d. D. Phys. Ges., Vol. 15, p. 560, 1913. 48 THERMIONIC VACUUM TUBE The presence of secondary electrons can easily be demon-strated by means of the circuit arrangement shown in Fig. plate P is kept at a constant positive potential with respect tothe filament F by the. battery E. When no potential differenceexists between filament and grid G, the cun-ent in the circuit FGAi
. The thermionic vacuum tube and its applications . ectrons strike the emitting electrode, be increased to asufficiently high value one primary electron can expel as many astwenty secondary electrons. »H. Dember, Verb. d. D. Phys. Ges., Vol. 15, p. 560, 1913. 48 THERMIONIC VACUUM TUBE The presence of secondary electrons can easily be demon-strated by means of the circuit arrangement shown in Fig. plate P is kept at a constant positive potential with respect tothe filament F by the. battery E. When no potential differenceexists between filament and grid G, the cun-ent in the circuit FGAis very small, because practically all the electrons emitted from thefilament are drawn through the openings of the grid and thrownon to the plate. If now the potential of the grid (positive withrespect to the filament) be increased the current to the grid ^ atfirst increases, as shown by the part OA in the curve in Fig. the grid potential reaches a certain value the current, asindicated by the ammeter A (Fig. 15) begins to decrease, drops.
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