G azərbaycan respublikasi təHSİl naziRLİYİ azərbaycan texniKİ universiteti M. M. QƏNDİLova e. Q. İsmayilova

Catching and Keeping Flying Particles
Sometimes, when an electron is moving at the right speed, a proton catches it, and keeps it circling round itself.

We call these two particles together-the electron and the proton-an atom of hydrogen, the simplest atom of all.

But one proton can't hold more than one electron. If another electron comes along it will fly past. The presence of neutron does not change anything in these rules.

But two protons can hold two electrons. The second electron will then be caught and will circle round. The atom of helium, the light gas with which airships are filled, has a strongly-bound group of two protons, two neutrons and two electrons.

Imagine now that we have more protons, neutrons and more electrons, protons and neutrons will catch the electrons, but the electrons will circle at a higher level.

Six protons can catch six electrons, two inside and four outside. This is an atom of carbon. Eight protons and neutrons can hold eight electrons: two inside, six outside. This is an atom of oxygen-a part of the air we breathe.

Ten protons and neutrons can hold electrons, two inside and eight outside. This is an atom of neon, which is also a part of the air we breathe.

Triodes
A third element-the-control grid was added between the cathode and plate of a diode and so it provided the resulting triode tube with the ability to amplify tiny signals. The control grid in this tube is a circular spiral of a number of turns of fine wire that completely surround the cathode. Because of its open construction the grid does not directly hinder the flow of electrons to the plate, but when a voltage is placed on the grid it has a profound effect on the electric field between cathode and plate and, hence, on the total electron

flow.

Since the control grid is nearer to the cathode than the plate, a potential placed on the grid has a much larger effect on the electric field within the tube-and hence upon the plate current-than the same potential placed on the plate. The grid thus has a controlling effect on the flow of plate current in the tube.

A triode requires three operating voltages, one on each electrode, to operate correctly. The plate of the tube is normally connected to a high positive voltage. E voltage ac or dc is connected to the filament or heater to bring the cathode to its proper emitting temperature and thus make available a supply of electrons.

Finally, a voltage is placed on the control grid to govern the flow of plate current. This voltage generally consists of two components. One is a fixed dc voltage, called the bias E which is normally a few volts negative with respect to the cathode. Its purpose is to operate the tube on a definite point on its characteristic curve so that a certain amount of plate current is always flowing.