Vaccum Tube is an electronic device in which the flow of electrons is through a vacuum is known as vacuum tube. A vacuum tube usually contains a cathode which is the electron emitter, an anode(plate) which is the electron collector and one or more electrodes (called grids) for controlling the flow of electrons between cathode and plate. These electrodes are housed in a highly evacuated glass envelope. The plate is held at positive terminal with respect to cathode so that emitted electrons are attracted to plate to provide current in vaccum.
