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AND AGAIN ... MOVING CHARGES
In an e-tube, as well as in the transistor, the amplification is obtained because a weak electrical signal controls the current flowing through the lamp current (charge movement), and this current can develop significant power at the expense of an external battery power.
Unlike the transistor, the basic processes in the tube do not occur in microscopic crystals of germanium or silicon, and in a vacuum - in a glass (or sometimes a metal-metal or) container from which air is pumped out.
In a transistor, and in particular, its emitter always has free electric charges, i.e. charges which can move under the influence of a voltage to form the emitter and collector current. In a vacuum, free of charge there is little, and to get them to introduce a special lamp detail - the cathode. In many lamps the cathode is a metal wire (there are other types of cathodes) in which an electric current is passed (heating current) by plugging in a small battery. Under the influence of the cathode current, like the electric coil is heated to high temperatures, from 800 ° to 2500 °, depending on the type of cathode. As you know, the metal is always a large number of free electrons (and distinguishes it from the conductors insulators), which move randomly in the interatomic space. The higher the temperature of the metal, the more intense it is random motion. At high temperatures, many of the cathode electrons are outside its scope, and in the vacuum near the cathode, there are free electric charges.
Now force the free electrons emitted from a heated cathode, orderly move in any particular direction, that is, the lamp will create an electrical current. To do this, place the bottle in one electrode - a flat metal plate, located not far from the cathode. This electrode is called "anode", and Two-electrode lamp, as well as semiconductor device with two zones, called a diode.
When inserted between the battery anode and cathode, where the "plus" of its link with the anode, under the influence of a positive voltage on the anode will move it to fly out of the cathode electrons, and they were replaced by the cathode electrons will flow from the other battery. Thus, inside the container and will appear in the external circuit current
known as the anode current. If you change the polarity of the battery anode - minus its anode connected to the tube - then no current in the lamp will not, as a negative voltage on the anode will no longer attract the electrons, which have, as you know, a negative charge. |