LEYDEN BOTTLE: PARTS, OPERATION, EXPERIMENTS - PHYSICAL - 2024

The Leyden bottle is a thin glass bottle or jar, which contains a tightly fitting metal foil on the inside and another tight-fitting metal film on the outside.

It is the first electrical device in history that served to store electrical charges simply by touching it, either by the rod or by the outer sheet, with a bar previously charged by friction (triboelectric effect) or by electrostatic induction. A voltage source such as a cell or battery can also be used.

Figure 1. The figure shows a typical Leyden bottle. The inner sheet is one of the capacitor plates and the outer sheet is the other plate. Source: Wikimedia Commons. Branch

History

The invention of the Leyden bottle is credited to Pieter van Musschenbroek, Professor of Physics at the University of Leyden in 1745. Independently and simultaneously, the German inventor Ewald Georg von Kleist also managed to store static electricity with similar bottles, anticipating the Dutch.

Musschenbroek had the help of a lawyer named Cunaeus, whom he had invited to his laboratory in Leyden. This sagacious character was the first to notice that the charge accumulated by holding the vial with his hand while the bar or needle was being charged with the electrostatic machine.

After Professor Musschenbroek surprised everyone with his invention, the next improvement on the Leyden bottle, as the device was finally christened, was made in 1747 thanks to John Bevis, a physician, researcher, and last but not least the astronomer who discovered the Crab Nebula.

Bevis observed that if you covered the outside of the bottle with a thin sheet, there was no need to hold it with your hand.

He also realized that filling it with water or alcohol was not necessary (the original Musschenbroek bottle was filled with liquid) and that it was only required to cover the inside wall of the bottle with metal foil in contact with the rod that passes through the cork.

Later experiments revealed that more charge accumulated as the glass became thinner and the adjacent metal surface more extensive.

Parts

The parts of a Leyden bottle are shown in figure 1. The glass acts as an insulator or dielectric between the plates, in addition to serving to give them the necessary support. The plates are usually thin sheets of tin, aluminum or copper.

An insulator is also used to make the lid of the jar, for example dry wood, plastic or glass. The cover is pierced by a metal rod from which a chain hangs that serves to make electrical contact with the internal plate.

Materials needed to make the Leyden Bottle

- Glass bottle, being as thin as possible

- Metal foil (aluminum, tin, copper, lead, silver, gold) to cover separately, the internal and external part of the bottle.

- Drilled insulating material cover.

- Metal rod to go through the perforated lid and that at the inner end has a chain or cable that makes metallic contact with the inner sheet of the bottle. The other end of the rod generally ends in a sphere, to avoid electric arcs due to accumulated charges on the ends.

Figure 2. Parts of a Leyden bottle. Source: Wikimedia Commons.

Functioning

To explain the accumulation of electrical charge it is necessary to start by establishing the difference between insulators and conductors.

Metals are conductive because electrons (carriers of elemental negative charge) can move freely within them. Which does not mean that the metal is always charged, in fact it remains neutral when the number of electrons equals the number of protons.

In contrast, electrons inside insulators lack the typical mobility of metals. However, by rubbing between different insulating materials it can happen that electrons from the surface of one of them pass to the surface of the other.

Returning to the Leyden bottle, in simplified form it is a metallic foil separated by an insulator from another conductive foil. Figure 3 shows a schematic.

Figure 3: Simplified diagram of Leyden bottle and how it acquires the charge. Source: Fanny Zapata.

Suppose the external plate is grounded, either by hand holding or by a wire. When approached by a rod that was positively charged by rubbing, the rod connecting to the inner plate becomes polarized. This leads to a separation of charges in the rod-inner plate assembly.

The electrons on the outer plate are attracted to the positive charges on the opposite plate and more electrons reach the outer plate from ground.

When this connection is broken, the plate becomes negatively charged and when the rod is separated, the inner plate becomes positively charged.

Capacitors or capacitors

The Leyden bottle was the first known capacitor. A capacitor consists of two metal plates separated by an insulator and they are well known in electricity and electronics as indispensable circuit elements.

The simplest capacitor consists of two flat plates of area A separated by a distance d much smaller than the size of the plates.

The capacity C to store charge in a flat plate capacitor is proportional to the area A of the plates, and inversely proportional to the spacing d between the plates. The constant of proportionality is the electrical permittivity ε and they are summarized in the following expression:

The capacitor formed by the Leyden bottle can be approximated by two concentric cylindrical plates with radii a internal and radius b for the external plate and height L. The difference in the radii is precisely the thickness of the glass d which is the separation between the plates.

The capacity C of a cylindrical plate capacitor is given by:

As can be deduced from this expression, the longer the length L, the more capacity the device has.

Leyden bottle capacity

In the case that the thickness or separation d is much less than the radius, then the capacity can be approximated by the expression of the flat plates as follows:

In the previous expression p is the perimeter of the cylindrical plate and L is the height.

Regardless of shape, the maximum charge Q that a capacitor can accumulate is proportional to the charge voltage V, the capacitor's capacity C being the constant of proportionality.

Q = C ⋅ V

Bottle of homemade Leyden

With readily available materials at home and some manual skill, you can emulate Professor Musschenbroek and build a Leyden bottle. For this you need:

- 1 glass or plastic jar, such as mayonnaise.

- 1 perforated plastic insulating cover through which a rigid wire or cable will be passed.

- Rectangular strips of kitchen aluminum foil to cover, stick or adhere to the inside and outside of the jar. It is important that the aluminum coating does not reach the edge of the jar, it can be a little higher than half.

- A flexible cable without insulation that is spliced ​​to the inside of the rod, so that it makes contact with the aluminum foil that covers the inside of the wall of the bottle.

- Metallic sphere (goes on top of the lid to avoid the effect of spikes).

- Cable without insulation that will be attached to the outer aluminum sheet.

- Ruler and scissors.

- Scotch tape.

Note: Another version that avoids the work of placing the aluminum foil on the inside is to fill the bottle or jar with a solution of water and salt, which will act as the inner plate.

Process

Cover the bottle inside and out with the aluminum foil strips, if necessary they are fixed with the adhesive tape, taking care not to exceed the middle of the bottle too much.

- Carefully pierce the cap to pass the copper wire or cable without insulating cover, to put the inner aluminum foil of the bottle in contact with the outside, where the conductive sphere should be placed just above the cap.

- More wire without insulation is used to bind the outer jacket and make a kind of handle. The whole assembly should look like what is shown in figures 1 and 4.

Figure 4. Leyden bottle. Source: F. Zapata.

Experiments

Once the Leyden bottle is built, you can experiment with it:

Experiment 1

If you have an old TV or monitor with a cathode ray screen, you can use it to charge the bottle. To do this, hold the bottle with one hand by the outer plate, while bringing the cable that connects to the inner part close and touching the screen.

The cable tied to the outside should be close to the cable coming from the inside of the bottle. Note that a spark occurs, showing that the bottle has become electrically charged.

Experiment 2

If you do not have a suitable screen, you can load the Leyden bottle by holding it close to a woolen cloth that you have just taken from the clothes dryer. Another option for the charging source is to take a piece of plastic (PVC) tube that has previously been sanded to remove grease and varnish. Rub the tube with a paper towel until it is sufficiently charged.

References

1. Leyden bottle. Recovered from: es.wikipedia.org
2. Electrical instruments. Leyden Jar. Recovered from: Brittanica.com
3. Endesa educates. Experiment: Leyden bottle. Recovered from: youtube.com.
4. Leyden Jar. Recovered from: en.wikipedia.org.
5. The Physics of the Leyden jar in "MacGyver". Recovered from: wired.com
6. Tippens, P. Physics: Concepts and Applications. 516-523.