Without understanding what current is, studying the physics- related section of physics is impossible. The concept of current is the basis on which, like a house on a reliable foundation, further calculations of electrical circuits are built and new definitions are given. The current strength is one of the values of the international SI system, therefore the universal unit of measurement is Ampere (A).
The physical meaning of this unit is explained as follows: a current of one ampere occurs when particles with a charge move along two conductors of infinite length, between which there is a gap of one meter. Moreover, the interaction force arising on each meter section of conductors is numerically equal to 2 * 10 to the degree of -7 Newton. It is usually added that the conductors are located in a vacuum (which allows you to level the influence of the intermediate medium), and their cross section tends to zero (the conductivity is maximum).
However, as it usually happens, classical definitions are clear only to specialists who, in fact, are no longer interested in the basics. But a person unfamiliar with electricity "gets confused" even more. Therefore, let’s explain what the current strength is, literally “on the fingers”. Imagine an ordinary battery, from the poles of which two insulated wires go to the bulb. A circuit breaker is connected to the gap of one wire. As you know from the initial course of physics, electric current is the movement of particles with their own electric charge. Usually they are considered to be electrons (indeed, it is an electron that has a single negative charge), although in reality everything is a little more complicated. These particles are characteristic of conductive materials (metals), but in gas media ions additionally charge (we recall the terms “ionization” and “breakdown of the air gap”); in semiconductors, conductivity is not only electronic, but also hole (positive charge); in electrolytic solutions, the conductivity is purely ionic (for example, car batteries). But back to our example. In it, the current forms the movement of precisely free electrons. While the switch is not turned on, the circuit is open, the particles have nowhere to move, therefore, the current strength is zero. But it is worth “assembling a circuit”, as the electrons rush from the negative pole of the battery to the positive, passing through the bulb and causing its glow. The force that makes them move comes from the electric field created by the battery (EMF - field - current).
Current strength is the ratio of charge to time. That is, in fact, we are talking about the amount of electricity passing through the conductor per unit time. We can give an analogy with water: the stronger the tap is open, the greater the volume of water will pass through the pipeline. But if water is measured in liters (cubic meters), then the current is measured by the number of charge carriers or, which is also true, by amperes. So simple. It is easy to understand that there are two ways to increase the current strength: removing the bulb from the circuit (resistance, obstruction to movement), and also increasing the electric field created by the battery.
Actually, we have come to how in the general case the calculation of the current strength is performed. There are many formulas: for example, for a complete circuit that takes into account the influence of the characteristics of the power source; for alternating and direct currents; for multiphase systems, etc. However, all of them are united by a single rule - the famous Ohm's law. Therefore, we present its general (universal) form:
I = U / R,
where I is the current, in amperes; U is the voltage at the terminals of the power source, in Volts; R is the resistance of the circuit or section, in Ohms. This dependence only confirms all of the above: an increase in current can be achieved in two ways, through resistance (our bulb) and voltage (source parameter).