Electric current



Current intensity is the electrical charge that passes through a section of the conductor per second.

The intensity is given by the following formula:

I = Q / t


I: Intensity expressed in Amps (A).
Q: Electric charge expressed in Coulombs (C).
t: Time expressed in seconds (s).

With this definition, we can say that an electric current has an intensity of 1 amp when a load of 1 colombium passes through a section of the conductor in 1 second.

How is the intensity of an electric current measured?

The intensity of an electric current is measured with the galvanometer. For a correct measurement, the galvanometer must be placed in series with the electrical conductor whose intensity is to be measured.

AmperageThe unit of measurement for intensity is Ampere A in the International System of Units. If the galvanometer is calibrated in amps it is called an ammeter.

Amps should not be confused with amp-hours. The ampere-hour is a unit that measures the amount of electrical charge that flows through a storage device if it supplies a current of 1 ampere for 1 hour. An ampere-hour equals 3,600 coulombs.

How is a current intensity generated?

Imagine two ends of the same conductor. Each end is subjected to a different electric field. Electric fields have a different electric potential. Due to this potential difference, the electrons present in the conductor experience attractive and repulsive forces. These electrical forces cause the free electrons to move.

The movement of these electrical charges is carried out with a certain speed. We consider any section located at a point between the two extremes. A certain number of electrons per second will pass through this section. Which is the same: a certain amount of electricity per second.

That amount of electricity per second is called the intensity of the electric current expressed in amps.

Two types of electric current can exist in an electrical circuit :

  • Direct current (DC).
  • Alternating current (AC).

What is the difference between current intensity and voltage?

Current and voltage are two different but related aspects of electrical energy. Voltage is the difference in electrical potential between two points, while current is the flow of electrical charges (or the  amount of electrical charge) through a conductive material .

Ohm's law

Along with resistance, they form Ohm's law that relates the three variables together.

Ohm's Law states that the voltage between two points of an element is equivalent to the resistance of the element multiplied by the current that flows through it.

Ohm's law

V: potential difference. Volts (V).
A: resistance. Ohms (Ω).
I: current intensity. Amps (A).

According to Ohm's law, the higher the voltage between the ends of the conductor, the greater the current flowing through the resistive circuit. The voltage is directly proportional to the magnitude of the current. The greater the resistance in the circuit, the greater the resistance in the circuit. That is, the electric current is inversely proportional to the magnitude of the resistance.

Example of current and voltage

To better understand what voltage is and what intensity is, we will explain it less by means of an example :

Let's say you have two water tanks. One is half empty while the other is full. The difference in water levels in the two tanks is similar to a voltage difference. And like water when given a path, the electrical potential would move from the point of greatest potential to the point of least potential until the two levels are equal.

What is the current density?

With the current density we can express the average current per unit of a conductor's bone. The current density is designated by the symbol J. In the definition of current density it is assumed that current flows uniformly through the conductor cross section.


J is measured in units of the International System in A / m 2 (amps per square meter). However, given the dimensions of the conductors, it is common to express it in A / mm 2  . Obviously, as it is the section of a conductor, it is more manageable to make the measurement in square millimeters.

The current density is an important value when calculating the section of a conductor through which a certain electric current has to circulate.

What is the impediment?

The impediment is the magnitude that determines the correspondence between the voltage and the intensity of the electric current. It expresses the relationship between the voltage and the intensity for a current, in a given time. Its module (sometimes called improperly impedance) establishes the relationship between the maximum values ​​or the effective values ​​of voltage and current.

In the international measurement system, the unit of measurement for impedance is Ohm.

Impediment is one of the most important characteristics of a cable. As well as for all the elements of the network, it indicates the resistance to the alternating current between wires that the cable offers at the different frequencies.


Published: November 17, 2019
Last review: March 29, 2020