Many of our contemporaries are so accustomed to the manifestations of the surrounding reality that to some extent they ceased to notice them. People live in expectation of something inexplicable, although real miracles surround us everywhere. What could be simpler than clicking the switch button so that the light bulb dispels the darkness in the room !? Or go up to the floor just by pressing a button in the elevator. Isn't it a miracle?
Although the duration of the practical use of electric energy by mankind is only a few hundred years, which is just a moment for history, many discoveries have been made during this time. Some are known even now (what is the famous Ohm's law!), While others are remembered only by historians and, occasionally, teachers in educational institutions. For example, what kind of associations will the average person have when they say “Leiden banks”? Financial institutions, medical devices, or maybe “tricky” containers for preserving vegetables? However, this is quite natural, because even not every electrician will guess that a Leyden can is a prototype of modern electric capacitors. Although the design is extremely simple, theoretically, with proper refinement, such devices can quite successfully work as part of electrical circuits.
Each student knows that if you rub a plastic handle on your hair, then when it approaches other objects, a spark will appear in the air gap. A similar principle is used in an electrophore machine, thanks to which a Leyden jar appeared. In the 18th century, the German Guericke demonstrated to a secular society the installation, which was based on a large ball made of glass with a mounted axis. The simplest belt drive made him spin. By touching a piece of skin, it was possible to cause the appearance of electric sparks and invisible electromagnetic fields. In objects located in the range of field strength lines, currents were generated and accumulated (condensed).
1745 is the date when the Leyden bank was opened. The physicist Mushenbruck from Leiden guessed to pour water into a jar, put a piece of wire there, gently take the container with his hands and bring it to the working electrophore. When touching the protruding part of the wire, the scientist received a strong electric shock. It is now clear that the human hands and water in the bank served as what are now called capacitor plates, and the glass wall of the vessel as an insulating layer. The Leiden bank could accumulate so much electricity that it was enough to go through a chain of 700 people. It was obvious that the potential of this discovery was enormous. It was in the city of Leiden that the production of such "capacitors" was established, which gave the name to the device.
2 years after the discovery of B. Franklin for the purpose of the experiment wrapped the outer walls of the cans with tin foil, thereby increasing the capacity. It was clear that much remained to be discovered. In fact, it was a trial-and-error path, and a theoretical justification was already derived from the results of experiments. Subsequently, Franklin replaced the can with flat glass with foil on opposite sides, obtaining a capacitor that is familiar to all of us.
Do-it-yourself jar can be made very quickly. You will need a plastic can, a tin plate with a soldered insulated wire, activated carbon, strong filter paper, a metal (or plastic with a conductive insert) lid with a pin-out and salt water. We lower the plate to the bottom of the plastic container, bring the free end of the wire up. Cover with paper on top, pour a layer of coal, pour salt water and place a lid with a conclusion. It turns out that two insulated wires come out of the can: from the lower and upper plates. Now, if external voltage is applied to them, part of it will condense. After that, it remains only to connect the load. When working with the "bank" you need to be careful.