Leyden jar

Many of our contemporaries are so used to the manifestations of the surrounding reality that they to some extent have ceased to notice them. People live in anticipation of something inexplicable, although the most real miracles surround us everywhere. What could be simpler than clicking the switch button so that the light bulb dispelled the darkness in the room !? Or go up to the floor by simply pressing the button in the elevator. Is not it a miracle?

Although the duration of practical use of electric energy by mankind totals only a few hundred years, which is only an instant in history, a lot of discoveries have been made during this time. Some are known now (which is the famous Ohm law!), While others are remembered only by historians and, occasionally, by teachers in educational institutions. For example, what kind of associations will an average person have with the words "Leyden banks"? Financial institutions, medical devices, or maybe "cunning" capacity for preserving vegetables? However, this is quite natural, because even not every electrician will guess that the Leyden bank is a prototype of modern electric capacitors. Although the design is very simple, theoretically, with proper refinement, such devices can work quite successfully as part of electrical circuits.

Every schoolboy knows that if you rub a plastic handle on your hair, then as it approaches other objects in the air gap, a spark will appear. A similar principle is used in the electro-machine, thanks to which the Leyden bank appeared. In the 18th century the German Gerike demonstrated to a secular society an installation based on a large ball of glass with a mounted axis. The simplest belt drive made it spin. Touching a piece of skin, you could cause the appearance of electric sparks and invisible electromagnetic fields. In the objects located in the zone of action of the lines of field strength, currents were generated and accumulated (condensed).

1745 is the date when the Leyden bank was opened. The physicist Mushenbrook from Leiden guessed to pour water into the jar, place a piece of wire there, gently take the container by hand 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 is now called the capacitor plates, and the glass wall of the vessel is an insulating layer. The Leiden Bank could accumulate so much electricity that it was enough to pass through a chain of 700 people. It was obvious that the potential of this discovery is enormous. It was in Leiden that the production of such "capacitors" was set up, which gave the name to the device.

Two years after the discovery, B. Franklin, for the purpose of experiment, wrapped the outer walls of the can with foil made of tin, thereby increasing the capacity. It was clear that there was still much to be discovered. In fact, this was the path of "trial and error," and the theoretical justification was already derived from the results of experiments. Subsequently, Franklin replaced the jar with a flat glass with foil on opposite sides, having received a capacitor familiar to all of us.

The Leiden bank with its own hands can be manufactured very quickly. You will need a plastic can, a plate made of tin with soldered insulated wire, activated carbon, a strong filter paper, a metal (or plastic with a conductive insert) cover with a contact terminal and salt water. We lower the plate to the bottom of the plastic container, the free end of the wire is drawn up. Top with paper, pour a layer of coal, pour salt water and place the lid with a conclusion. It turns out that two insulated wires come out of the jar: from the bottom and top plates. Now, if an external voltage is applied to them, then part of it will condense. After that, it only remains to connect the load. Care should be taken when working with the "jar".