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Polarisationmeaning

The critical symbol here is the “DC” symbol. Before we move on to the cables, let us start with devices such as DC sources, for example. They should be visibly marked on the housing (nameplate) with the symbol of the current they require at the input (if they need it) and the current at their output – international AC and DC codes are used to inform users about it. One example is a phone charger, which is connected to the 230 V / 50 Hz AC power supply in our sockets and to which – on the other end – we connect a mobile phone, which receives DC from its output. This type of power supply (which is the most common source of direct current beside cells) can, for example, have a label on the input that reads “INPUT 100-240 V ~50-60 Hz 0.6 A” and a label on the output that reads “OUTPUT DC 5 V ... 3.0 A”. Moreover, in the technical specifications of phones, there is information regarding their electric current requirements. The DC symbol also appears there, which informs the user that the device requires DC power. In short: every device, appliance and component running on direct current should be labelled with the abbreviation DC or its graphic equivalent “ ... “.

Polarisationexamples

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About the DC cords, we must remember that we have “+” and “-” potentials, which means that each cord must be distinguishable in some way from the other. This is, of course, a matter of safety when repairing or assembling the device, and when using or extending the installation.

The current standards following the 2007 unification state that wires with positive potential must be red, while wires with negative potential must be blue or black (it is about the insulation of these wires, not the wires themselves). Many manufacturers also use additional labels, e.g. imprints with the symbols “+” and “-” or “L+” and “L-”. Sometimes both wires are in black insulation, so the one with negative potential should be marked with a dashed line for easy distinction.

Polarisationin politics

Without polarisation, i.e. uneven distribution of electrons, the flow of the electric current would be impossible. Remember that in this text, we will only discuss the DC, which is used by virtually all electronic components and generated by all batteries and rechargeable batteries or power supplies, used, e.g. to charge smartphones. In this case, the electrons flow from the “+“ to the “-“ pole, and the flux does not change its direction or magnitude cyclically. It is constant and is presented on the graph as a straight line parallel to the time axis.

Polarisationin physics

In the case of insulators, the electric field induces a much weaker polarisation, called atomic polarisation, because it results from whole atoms with different electrical charges moving slightly towards each other rather than free electrons moving. Insulators’ polarisability, i.e. the tendency of electrical charges to get distorted, or separated in an orderly manner, is so small that it may be ignored. In addition to typical dielectrics, there are other kinds, such as e.g. piezoelectrics and pyroelectrics, in which polarisation is induced by mechanical stress (the former) or temperature changes (the latter).

Finally, let us mention the electrolytes and their ionic conductivity. These substances may be found in capacitors and batteries, among others. The ionic conductivity of electrolytes is accompanied by ions moving due to current flow-induced electrolysis. Such movements involve the separation of positive and negative ions, resulting in a polarised system in which two distinct poles can be distinguished.

The term "polarisation" comes from "a pole" (Latin: “polaris”), which means "either of two related opposites, extremities of an axis or two opposites of a physical feature (magnetism, electrostatics)". In electronics or solid-state physics and electromagnetism, polarisation is a fundamental phenomenon without which these fields would not exist and develop. DC flow and, consequently, all signal processing technology is based on polarisation. Thus, understanding its function and relevance to electronic components is essential. The topic is extensive, so this time we will only focus on a few issues that are crucial for beginners in the world of electronics: how to label polarised components, the hazards associated with improper polarisation and the methods to prevent them.

Firstly, we need to remember that some materials are excellent conductors, and electric charges in them can be polarised very easily. In contrast, other ones are insulators (dielectrics) in which polarisation is difficult to achieve, although not impossible to some extent. The first group includes metals (iron, gold, silver, copper) and ionic conductors (salt water), while the second group includes many plastics (PVC, Polyamide, Polyethylene, and Polyurethane). By applying an electric field to a conductor (for example, a piece of metal), we induce electron polarisation, which means that negatively charged clouds of free electrons detach from the positively charged atomic nuclei and accumulate in one region – the wall of the conductor, where they increase the density of the negative charge pole. The electron-deficient atomic nuclei represent the positive pole.

Polarisationin Chemistry

Polarisation is the separation of the elements of a system into two groups of opposing natures. This is what we see when we analyse the definition of electric voltage, understood as the difference in electric potentials between two points in an electric circuit. These two points are the polarised (opposing) regions, one with a significant accumulation of negatively charged electrons and the other one with their deficiency. This can be compared to the ends of an AA battery, one marked with a “+” symbol and the other with a “-“. As you can easily guess, these are opposite poles (polarised points), where the “minus” end of the battery is the region of electron accumulation, and the "plus" one is the region where electrons are missing. The polarisation in batteries is constant because we have DC there, which always flows in the same direction – from the positive to the negative pole. In the case of alternating current (such as that found in our household electrical sockets), we also observe polarisation, but periodically alternating one. The periodicity (frequency) of the changes in the polarisation of AC is indicated by the symbol "Hz", which (in this case) has the value 50 next to it, meaning that in one second, there are 50 cycles of the polarisation changes. In each of these cycles, the electrons move first in one direction and then in the opposite direction, after which everything returns to the starting point, and the next cycle begins.

A critical risk when supplying electronic components with DC power is the risk of reverse-potential connection and (consequently) damage to the systems in operation. This is why manufacturers use specific methods to recognise polarisation and distinguish between positive and negative potential. The first and most obvious way is to mark the wires with colours or symbols, as described above. Another way is to apply the symbols “+” and “-“ in the respective places. The third one is to make wires or pins/leads of different lengths (in the case of components such as capacitors and light-emitting diodes). The longer pin/lead is the positive pole (anode), and the shorter one is the negative pole (cathode). However, all such labels may prove unreliable: prints may wear out, pins may become chipped or broken, wires may be swapped for others of different colours and lengths, and so forth. Therefore, there is a need for safety solutions to protect users against the effects of reverse polarisation, like those that only let the current flow in one direction. One such solution that can be used when designing electronic equipment is a circuit with a diode that conducts current and allows the receiver to be powered when the polarisation is correct. In contrast, when the polarisation is reversed, it causes a significant voltage drop, so that the receiver is protected. There are also circuits with diodes that do not cause any voltage drop, but when the power supply (e.g. a battery) is reversed, they take all the current and blow the receiver-protecting fuse. Other solutions are MOSFETs incorporated into the circuit at the “plus” or “minus” pole. They limit the current when the poles are reversed.

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Through the power connector, polarised DC reaches the electronic circuit. Although such connectors may also provide a signal transmission function, their primary role is to allow charge to flow from the power source to the connected device or electronic circuit that requires direct current. For this reason, the power connector should not be designed just at random, but must have clearly marked components through which positive potential flows and separate parts for the flow of negative potential. As a result, all power connectors in electronics must be polarised, for example, the power plugs (and sockets) of many electronic devices, such as TV set-top boxes, cameras, smartphones and many others. Their power supply plugs are virtually always fitted with a “minus” inside (the pin) and a “plus” outside (the outer rim). Clear labelling is a good practice among manufacturers, but it is not a rule. It sometimes happens (although very rarely) that the polarity of the plug is reversed. Still, usually, it causes no damage, as power input protection is commonly used to block reversed DC voltage. Power supplies equipped with polarity switches are also an interesting solution – they can be freely adapted to suit every variant.

Polarisation is, therefore, a ubiquitous phenomenon. It is helpful to see it as the ordering of electrical charges within a particular space or object into two separate and opposing regions, one representing an accumulation of negative charges and the other one – positive charges.

Electronic circuit components are polarised. Therefore, obviously, they “operate” on a polarised direct current (DC). As a perfect example, LEDs must be connected correctly to DC leads: each of its two electrodes (cathode and anode) must meet the “plus” and “minus”, respectively. The same is true for polarised capacitors, which, unlike bipolar capacitors (the direction of connection does not matter), are characterised by specific polarisation that must be maintained. These are usually electrolytic capacitors of large capacitances, which are nevertheless very susceptible to damage if reversely connected to power sources. Of course, their polarisation is clearly marked, e.g. by the pins/leads of different lengths.