# What does the term 'current strength' mean

Without understanding what current is, the study of the branch of physics connected with electricity is impossible. The concept of current is the basis on which, like a house on a reliable foundation, further calculations of electric circuits are built and new and new definitions are given. Current strength is one of the values of the international SI system, so the universal unit of measurement is Ampere (A).

The physical meaning of this unit is explained in the following way: the current strength in one amperes arises when motion of the particles possessing a charge along two conductors of infinite length, between which the gap is one meter. In this case, the interaction force arising on each meter section of the conductors is numerically equal to 2 * 10 to the power of -7 Newton. It is usually added that the conductors are located in a vacuum (which makes it possible to neutralize the effect of the intermediate medium), and their cross section tends to zero (with the conductivity being maximal).

However, as it usually happens, classical definitions are clear only to specialists who, in fact, are no longer interested in the basics. But a man unfamiliar with electricity will "get confused" even more. Therefore, let us explain what is the current strength, literally "on the fingers". Imagine an ordinary battery, from the poles of which to the light bulb there are two insulated wires. A breaker is connected to the break of one wire. As is known from the initial course of physics, an electric current is a motion of particles possessing their own electric charge. Usually they are considered to be electrons (in fact, it is the electron that has a single negative charge), although in reality everything is a bit more complicated. These particles are characteristic for conductive materials (metals), but in the gas medium, charge ions are additionally transferred (remember the terms "ionization" and "air gap breakdown"); In semiconductors, the conductivity is not only electronic, but also a hole charge (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 motion of precisely free electrons. As long as the switch is not on, the circuit is open, there is nowhere to move the particles, hence the current strength is zero. But it's worth "assembling the circuit", as the electrons rush from the negative pole of the battery to the positive, passing through the light bulb and causing its glow. The force that causes them to move comes from the electric field created by the battery (EMF - field - current).

The current strength is the ratio of the charge to time. That is, in fact, it is a question of the amount of electricity passing through the conductor per conventional unit of time. One can draw an analogy with water: the more the faucet is opened, the greater the volume of water will pass through the pipeline. But if water is measured in liters (cubic meters), then the current is the number of charge carriers or, which is also true, amperes. It's that simple. It is easy to understand that the current can be increased in two ways: removing the bulb from the circuit (resistance, obstruction to movement), and also by increasing the electric field created by the battery.

Actually, we have come to how, in the general case, the calculation of the current 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 AC and DC currents; For multiphase systems, etc. However, all of them are united by a single rule - the famous Ohm law. Therefore, we give its general (universal) form:

I = U / R,

Where I is the current, in Ampere; U - voltage at the terminals of the power supply, in Volts; R is the resistance of the circuit or section, in Ohms. This relationship only confirms all of the above: increasing the current can be achieved in two ways, through the resistance (our light bulb) and voltage (source parameter).