Search results
State the principle of thermionic emission and the Edison Effect and give the reasons for electron movement in vacuum tubes. Identify the schematic representation for the various electron tubes and their elements.
Cold-cathode (field emission): electrons pulled out of material by strong positive potential. Thermionic – heated material transfers energy to electrons causing them to escape. Number of electrons depends on temperature and type of material. Almost instantaneous electron-emitting temp. AC voltage causes varying emission.
A vacuum tube contains two or more metallic elements enclosed in an evacuated envelope of glass, metal or ceramic material. (One of the metallic elements serves as a source of free electrons.) The more inclusive term, electron tube, describes any vacuum or gas filled device in which electrons move through space between elec trodes.
The operation of electron tubes, also referred to as vacuum tubes, depends upon the current associated to a stream of electrons, negative charged elementary particles, flowing from the surface of an electrode, referred to as cathode, to another electrode, called anode. The emission of electrons takes place from the surface of the cathode
Vacuum tubes mostly rely on “thermionic emission” of electrons from a hot filament or a cathode heated by the filament. This type is called a thermionic tube or thermionic valve. The simplest vacuum tube, the diode, contains a hot electron-emitting filament (cathode), and a cold plate (anode).
As the name implies a vacuum tube operates in a vacuum. This allows the electrons (e−) to flow freely between the electrodes in the tube without being impeded by gas molocules. That vacuum is usually contained in a glass envelope, though sometimes we find them in metal cans.
People also ask
How do electrons move in a vacuum tube?
What causes a vacuum tube to emit electrons?
How does a vacuum tube work?
What is electron motion in a vacuum tube?
How do secondary electrons affect a vacuum tube?
Which element provides the conduction currents of a vacuum tube?
Electrons and ions move at great velocities in even moderate-strength fields. For example, an electron dropping through a potential difference of 2500 V will achieve
