Vacuum Tubes and Thermionic Valves
Category : JEE Main & Advanced
(1) Those tubes in which electrons flows in vacuum are called vacuum tubes.
(2) These are also called valves because current flow in them is unidirectional.
(3) Vacuum in vacuum tubes prevents the emission of secondary electrons and burning of heated filament (which will happen if we use air in place of vacuum)
(4) Every vacuum tube necessarily contains two electrodes out of which one is always electron emitter (cathode) and another one is electron collector (anode or plate).
(5) Depending upon the number of electrodes used the vacuum tubes are named as diode, triode, tetrode, pentode.... respectively, if the number of electrodes used are 2, 3, 4, 5..... respectively.
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