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Electric Current

Electric current

Electric current is the flow of electric charge that passes through a material per unit of time. Moving electrical charges produce a magnetic field.

Electric charge is the physical property that certain subatomic particles (such as protons and electrons) possess. This property manifests itself manifested through the forces of repulsion and attraction that exist between them through electromagnetic fields. Protons are positively charged and electrons are negatively charged. This allocation of charges was made arbitrarily.

Anyway, when we talk about electric current, these electric charges are normally electrons.

For the electric charge to move it must be subjected to a potential difference.

How is electrical current measured?

Two quantities are defined from the electric current:

  • Current intensity
  • Current density

The current intensity (I) in a given section of a conductor (s) is defined as the electric charge (Q) that the section passes through in a unit of time (t):

The current density (j) is the intensity of current through a section per unit area of ​​the section (S).

In the international system of units the electric current is expressed in coulombs per second (C / s), that is, in Amps (A).

The galvanometer is the instrument to measure the intensity of an electric current. The galvanometer that has been calibrated in amps is called an ammeter.

What biological effects does it produce in humans?

The effect and possible danger of electricity on the human body results, among other things, from the influence on the excitation conduction system of the heart. In the heart, excitations are transmitted as electrical impulses, leading to an orderly contraction of the heart muscle.

Electricity supplied from outside interferes with this spread of excitation, especially if it is during the so-called vulnerable phase. In this phase, some parts of the heart are still excited, that is, they cannot be excited again, while other parts are already on their way to the unexcited state, that is, they can be partially excited again.

If additional excitation is activated in the vulnerable phase, it can cause disordered excitations of the cells of the heart muscle, ventricular fibrillation. Blood cannot be pumped due to uneven and rapid contractions of the cells of the heart muscle.

The particular danger of alternating current versus direct current results from the fact that alternating current is more likely to reach the vulnerable phase due to the rapid change in polarity.

The consequences of an electrical current accident in humans depend on several factors, in particular the type and frequency of the current and the period of time that the current affects the body. This explains why, for example, an electric shock caused by an electric grass fence has no lasting effect on humans or animals, as the current impulses are too short to excite nerve cells.

Finally, the path the current takes through the body also plays a role, with the vertical path in which the current flows through all vital organs being the most dangerous.

Ultimately, the current intensity per area, that is, the current density, and the duration of its action determine the effects. For example, high currents at the input and output points cause burns to the skin, which are called electrical marks.

If, for example, the electrodes are implanted under the skin or even close to the heart or other sensitive organs, the magnitudes of leakage currents that are still allowed in conventional appliances can be life-threatening.

History of electric current

Initially, electric current was defined as a flow of positive charges. The conventional direction of current flow was set as a flow of charges from the positive to the negative pole.

Later, thanks to the Hall effect, it was observed that in metals the charge carriers were electrons, with a negative charge. The electrons move in the opposite direction to the conventional one. This discovery contradicted what was previously established since in this way the electrons would move from the negative pole to the positive pole.

The first experiments with electricity were carried out in the 18th century. Back then, only electrical charge generated by rubbing (static electricity) or induction was available. The first constant charge movement was not achieved until 1800 thanks to the first electric battery invented by the Italian physicist Alessandro Volta.

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Published: March 13, 2017
Last review: March 27, 2020