Electricity is the most used form of energy by man. Without exaggeration, we can say that the definition of electric current as the ordered movement of electrons is well known even from the school physics textbook. But here is what voltage is and how this “ordered movement” is ensured, not everyone will answer. Recall that an electron, an elementary electric charge, does not move by itself along a conductor. On the other hand, only the movement of charges along the chain is accompanied by the performance of useful work in the form of the conversion of energy from one type to another. It is thanks to these transformations that the electric current in some cases glows the filament of the light bulb, and in others it rotates the rotor of the electric motor. In the first case, we have the conversion of electrical energy into heat, and in the second - into magnetic. The energy of moving charges is consumed by a source that maintains an electric current in the circuit. Flowing along the conductor, the current transfers the energy of the EMF source to the consumer - filament, motor windings, etc.
If we define the current as the number of charges flowing through the conductor, then we can say that the current depends on the number of these charges per unit time. And what does the electric current in the circuit depend on? Consider the current flow model using the example of a water jet flowing from a hole in the bottom of a cylinder filled to the top. Imagine that in our model a cylinder is a conductor, and water is a large number of electron droplets. Then it is completely clear that the amount of water flowing out per unit time depends on two parameters - the pressure of the water column, which is referred to as voltage in electrical circuits, and the diameter of the hole - an analog of electrical resistance. The height of the water column in this model determines the upper potential of the energy source, droplet-charges are similar to the flow of electrons that move from the upper layer to the lower. The potential energy of the water mass, i.e. the ability to do some useful work is different at the upper and lower levels. Due to the potential difference, water can flow out of the hole and with the conversion of the potential energy of the water column into the kinetic energy of the water jet. If the height of the water column is increased, then the potential difference, or voltage, increases, and the current strength, more precisely, the mass of water flowing out per unit time also increases. Thus, the proposed model shows a directly proportional dependence of current strength on voltage.
In the theory of electricity, this conclusion is written as follows: I = f (U) * K, where I is the current, U is the voltage, and K is the individual response of the electric circuit to the passing current - conductivity. In the technique, the inverse of the conductivity R = 1 / K is usually used, and it is called "resistance". Resistance is usually interpreted as the payload of the circuit. In our model, such a “resistance” is the area of the hole for draining water: the larger it is, the greater its permeability, or, in the language of electrical engineering, conductivity, and therefore, resistance to water flow decreases.
The model clearly shows how the potential energy of the droplet-charge flow is converted into the kinetic energy of the outgoing jet. The lower the resistance (or the greater the conductivity), the more mechanical work is performed on the mass of water. In other words, different types of payloads are current converters, for example, an incandescent filament converts electrical energy into heat and light, a relay coil converts electrical energy into magnetic, etc.
Returning to the electrical circuits, we can conclude that the current strength I and voltage U are electrical parameters that determine the operation of current A (A = U * I).
In this case, the current strength is determined by the amount of charge transferred, and the voltage is the reason that makes the electrons "orderly" move from a larger potential to a smaller one. If there is no voltage, then no amount of free electrons in the substance will not lead to the movement of charges. This means that the lack of voltage does not result in energy transfer.
Hydroelectric power plants are a good demonstration of the findings: they are built using a large difference in water levels (potentials). Here, the mass of falling water is similar to current, and the difference in the levels of the upper and lower pools plays the role of a potential difference.