The B voltage gives the plate a positive charge to attract electrons from the filament.
When you connect the A battery, the filament of the tube is heated to release negatively charged electrons.
Electrons travel through the partial vacuum inside the tube, flowing from the filament to the positively charged plate.
Many tubes also have small structures, known as grids, between the filament and the plate.
The Crookes tube is in principle an Edison lamp with the filament broken.
Close to the filament is a graphite disk which serves as one of the electrodes.
Here the vegetative filament puts out two protuberances, which become shut off from the body of the filament by partitions.
The filament current of an audion-bulb averages about one ampere.
A filament of flame darted down the dark skies one moonless night and those who saw it believed, at first, that it was a meteor.
When the filament breaks, an electric lamp will no longer glow.
filament fil·a·ment (fĭl'ə-mənt)
A fibril, fine fiber, or threadlike structure.