What is a battery?
The battery can be regarded as a container of dissolved agent (acid, base or salt) wherein two plates of different metals are partly immersed [footnote 1]. Instead of one metal plate, a graphite rod can also serve. Just as there is an exception to every rule, so it is in the electromagnetism. Coal is a special and unique case of a non-metal that is a conductor of electricity. Consequently, it is also a good electrode in a battery.
[ [footnote 1] According to the etymological meaning of the words, what we describe here should not be called a battery, but a cell (an electrochemical cell). A battery is a multi-cell set. For example, the car battery is exactly that - a multi-cell set. ]
As the electricity can be produced by rubbing a woolen or other cloth against amber, vinyl, glass, PVC etc. so it arises here also through friction between the agent and the metal surface. The difference is that in the first case there is a mechanical, whereas here it is a chemical friction (so I call the chemical reaction). But since two dry substances cannot rub chemically, the battery jar must contain water. In the case of the mechanical friction everything has to be well dry, here everything has to be well wet (don’t be confused by the expression “dry cell”; it is also wet).
When two metal plates (say copper and zinc) are partly immersed in a dissolved agent, then the part of the copper plate outside the liquid is polarized in one sense (plus +), the immersed part in the opposite sense (minus -). For the zinc plate applies the opposite. Plus means blowing, Minus means suctioning (in relation to this, please see What is an electric wind?). The two metal plates of the battery can be imagined as two fans. The one that is blowing outside the liquid (positive electrode = copper), it is suctioning inside the liquid; the one that is suctioning outside the liquid (negative electrode = zinc), it is blowing inside it. When the electrodes are connected with a metal wire, a closed flux is created. The Plus is the strongest near the positive pole and, as we move away from it through the wire, its strength continuously decreases. The same applies to the Minus, but starting from the other pole. Figuratively, we can represent it this way:and
The closed flux will circulate until one of the plates is consumed or until the agent has transformed into something else and thus has lost its aggressiveness. These two processes are interconnected and take place simultaneously. In the agent there is motion of matter. For comparison and better understanding, we use another natural phenomenon, the waves in the oceans. The water level rises and falls and we cannot say that the water moves toward the coast with the speed of the wave. However, an object floating on the water will move with each wave a little onwards until it eventually reaches the coast. (in relation to this, please see).
At the same time the negative electrode wears off, which is understandable, because its part inside the solution behaves as positive and the movement is always from the positive to the negative. If we open a "dead" carbon-zinc AA battery, we will see that the zinc jar (the negative pole) is completely dissolved, while the carbon rod (the positive pole) in the middle is quite good. Certain non-metals when rubbed with some cloth have the intrinsic tendency to plus (glass, leather, nylon), others to minus electricity (amber, vinyl, silicone, teflon, PVC, etc.). For metals we cannot speak in the same sense of the tendency to plus or to minus, because, as we see, the two polarities manifest here simultaneously. However, if we speak of the polarity of the metal plate outside the liquid, we can say that gold, silver, copper, platinum and carbon among others have intrinsic plus tendency, while zinc, lead, aluminum, tungsten, iron etc. have minus tendency.
Let us now consider the following experiment. We need three metal plates (a copper, zinc and a lead plate) and a small container with vinegar. First, we dip the copper and the zinc plate partly in the vinegar and connect them to a voltmeter: the copper plate to the (+)input, the zinc plate to the (-)input of the instrument. A voltage of about +0.93 V is measured. Then we do the same with the other two possible combinations. In the combination of copper and lead plate we measure about +0.43V when the copper plate is connected to the (+)input of the instrument, and in the combination of lead and zinc plate about +0.50V when the lead plate goes to the (+)input. In all cases the copper plate behaves like a (+)pole, the zinc plate like a (–)pole, only the lead plate in one case behaves like (–), in the other like (+)pole. On the horizontal axis of a graph we mark copper with +0.2, lead with –0.2 and zinc with –0.7 and see that the difference between copper and lead is 0.4, between copper and zinc 0.9 and between lead and zinc is 0.5, which is nearly consistent with the results of the voltage measurements. Therefore, we conclude that copper has the tendency to plus, lead the tendency to minus and zinc has a strong tendency to minus.
In the third case of the experiment (Pb-Zn), we saw that the lead plate behaved as a (+)pole. Here a reversal of polarity of the lead plate takes place. The strong minus of the zinc plate reverses the weak minus of the lead plate converting it into plus. Let's compare that to the fans. Two fans with electric drives, one strong, the other weak, both are suctioning, are moved towards each other. The stronger will then force the weaker to turn in the contrary direction, i.e., to behave as a (+)blowing force in the interspace. If the strength of the stronger is 0.7 units and that of the weaker 0.2 units, then the strength of the stronger will decrease by 0.2 units in the interspace because part of its force it is using to overcome the power of the weaker. In the case of copper and zinc, there is another configuration because their forces add up (0.2 – (–0.7) = 0.2 + 0.7 = 0.9).
A reversal of polarity is also seen on magnets: a strong neodymium magnet reverses the polarity of a small and weak Al-Ni-Ko magnet, but in this case the reversal is permanent.
If we connect the poles of a 1.5 volt carbon-zinc battery with a good conducting wire (so-called short circuit), then the battery voltage will fall rapidly, but will remain at a certain value considerably less than the initial. If we break the circuit, the voltage soon returns to the initial value. Connecting the battery poles with a wire of very high resistance, the voltage of the battery will not fall. We can compare this to a container filled with water. If an outlet is located in the lower part of its lateral wall, the force with which the water flows out (determined by the reach of its jet) depends only on the height of the water level, which also represents the pressure on the outflow point. The container is not large and, as the water flows out, the water level and thus the pressure decreases, which reduces the jet reach. Let's imagine that the water column is quite high and that, as we open the outflow, a steady flow of water into the container begins; this inflow is smaller than the outflow of water in the first moments. As the water level drops, so does the intensity of the outflow, thereby at a certain moment the inflow and the outflow equalize and from then on the level but also the jet remain unchanged. Let us imagine another situation. Instead of a water container we have a huge lake with sufficient inflow and an outlet in the lower part. The force of the water jet with unchanged size of the outlet will always be the same; it is so because the water drain has no, or only a negligible effect on the level of the lake.
Let's get back to the battery. The fact that we cannot get more than 1V from copper, zinc and an acidic solution is a good example of the limitations that exist in the real physical world, and that must always be kept in mind if one doesn’t want to lose touch with reality. Also, in our water example, we cannot construct a container that reaches sky-high even with the latest technology; the container will always have a limited height and at some point the water will overflow.
We compare the size of the outlet to the conductivity of the wire. The larger the outlet is, the greater the conductivity. The intensity of inflow into the container we compare with the friction intensity of the agent with the metal plates. If we make a battery with larger plates in a larger container, but also with a more aggressive agent (sulfuric acid, for example, is much more aggressive than vinegar), then we have more intensive friction (i.e. more intensive “inflow”) and the voltage to which the initial voltage will fall when connecting the battery poles with a good conducting wire will be higher compared to the case with the smaller plates and the less aggressive acid [footnote 2]. Hence, the current will be stronger, too. With a huge battery, the voltage will not drop at all (this is the case with the huge lake). To achieve a voltage greater than 1 volt, we need to connect two or more cells in series. So we can get higher voltages only in steps: 2, 3, 4 volts. The parallel connection of two cells (plus connected to plus, minus to minus) which deliver the same voltage is the same as if we would have increased the dimensions of the plates and the container of a single cell. Increasing the dimensions of a cell also affects its power output, inasmuch as with a larger cell a bulb will shine longer before it begins to dim. The unit of measurement for this value is called ampere-hour (Ah). If a battery has 10 amp-hours, it means that it can supply current of one amp for 10 hours. Of course, this is an ideal value, since the voltage and thus the current gradually drops, and so the luminosity. However, if the battery delivers half an amp for two hours, that's one ampere hour too.
[Footnote 2] The described battery filled with vinegar is unusable for practical purposes because the vinegar is a very weak agent, i.e. the “inflow” in the battery is very low. No matter which bulb we connect to this battery, its voltage will immediately drop to zero and the bulb will not light up. Nevertheless, this battery shows the same voltage on the voltmeter as the one with the more aggressive agent, such as sulfuric acid. The measuring of the battery voltage we can compare with the measuring of the pressure at the lateral bottom point of an opaque container whose water level is unknown. At this point, we pierce a fine hole with a very thin needle and determine the water level in the tank according to the jet reach. Before that, through experiments with foreknown water levels (i.e. pressure values) we had set a scale of the jet reach at the same pinhole. With this scale we can also determine the pressure in the opaque tank, i.e., the unknown level when we make a hole with the same needle. Since the jet is very thin, the outflow won’t have a significant effect on the water level even of a very narrow tank. When we measure the voltage of a battery, we actually connect it to a great resistance (which we can think of as an extremely thin and long wire), measuring the strength of the current through it on the basis of the scale previously set. Although the bulb is also an extremely thin wire, its resistance is still low because of its shortness. Therefore, its connection to the vinegar battery is comparable to a larger hole in a narrow tank with water, in which there is also a very low inflow, resulting in the level falling immediately to zero.