Some materials conduct electricity because they have free charges (electrons) that can move easily, as is the case in metals. Materials that do not conduct electricity do not have these free charges or their electrons are strongly bound to the atoms, as is the case in insulators.
The way a material conducts electricity starts directly at the level of atoms. Each atom has electrons, those tiny negative particles that orbit around the atomic nucleus. Some of these electrons are strongly bound to the nucleus, but others, called free electrons, move easily from one atom to another: these are the real players in electrical conduction. The more free electrons a material has available, the more easily it can carry electric current. Conversely, if there are hardly any free electrons, the current doesn't pass well, or not at all. Metals like copper or silver have many free electrons, which explains why they are good conductors.
Conductive materials, like metals, allow electrons to flow freely thanks to their free electrons, which facilitates the easy passage of current. Insulators, on the other hand, keep their electrons tightly bound to their atoms — making it difficult to move them, so electric current barely passes through. In between, we have semiconductors: they hesitate a bit. Generally, they block current like insulators, but with some stimulation (heating, light, or the addition of impurities), they can allow current to flow, without reaching the fluidity of metals. Their ability to switch between these two behaviors makes them absolutely essential in modern electronics.
The electrons in a material are distributed into two main zones called bands: the valence band where they are mostly fixed in place and the conduction band where they can move freely. Between these two bands, there is often an empty region, the famous band gap. Its size changes everything: when it is really narrow or almost nonexistent, electrons easily jump to the conduction band, and the material then becomes a good conductor. But if the band gap is wide, it’s really tough; almost no electron can cross it, resulting in an insulating material. When the band gap is intermediate, neither too narrow nor too wide, we get that famous state in between: a semiconductor. The nice thing is that it opens up many possibilities to control their electrical behavior, because with a little energy boost (heating, light, etc.), these materials become decent conductors.
The more you heat a material, the more you agitate the atoms it contains. This agitation complicates the life of free electrons, as they find it increasingly difficult to move around freely. As a result, in a metallic conductor, increasing the temperature generally reduces electrical conductivity.
Surprisingly, it's the opposite in semiconductors. For them, heating a little means awakening the electrons trapped in the forbidden band and making them mobile. The result: more heat, more conduction! It's like shaking a tree to pick ripe fruit.
For insulating materials, temperature alters their electrical behavior very little. The electrons are so trapped that they remain immobile even if it gets a little hotter.
If you intentionally add certain impurities to a material, what is called doping, you will modify its electrical properties. For example, in semiconductors like silicon, adding a few specific atoms can create additional free electrons (n-type doping) or generate "holes" that facilitate the movement of positive charges (p-type doping). The result: you significantly increase the conductivity of the material, and you gain precise control over its electrical behavior. This is exactly how your electronic chips and transistors work. In contrast, having unwanted impurities often tends to block or disrupt electrons, which reduces the quality of your conduction.
Pure water is actually a very poor conductor of electricity: it is the salts dissolved in the water that allow electric current to flow easily. That's why tap water conducts better than distilled water!
Superconductors allow the flow of electric current without any resistance when they are cooled to very low temperatures. This means that they could theoretically transport electricity without any energy loss!
Some insulating materials can become conductive when subjected to high pressures or elevated temperatures. This is the case, for example, with diamond, which is normally an insulator but can be made conductive under extreme conditions.
Do you know that gold is not the best electrical conductor known? Silver ranks first with higher conductivity, but its cost and tendency to oxidize limit its use in certain cases.
Doping is a process that involves introducing small amounts of specific impurities into a semiconductor to enhance or control its electrical conductivity. These impurities add or remove electrons, forming positive (p-type) or negative (n-type) regions, which are essential for creating electronic components such as diodes and transistors.
A semiconductor is a material whose conduction properties lie between those of a conductive metal and an insulator. It can modulate its electrical conductivity through the addition of impurities (doping) or depending on the temperature, making these materials essential for the manufacturing of electronic devices such as transistors and diodes.
The temperature influences the conductivity of materials differently depending on their type. In metallic conductors, an increase in temperature generally decreases conductivity by intensifying atomic vibrations, which hinders the movement of free electrons. In contrast, for semiconductors and certain insulators, a rise in temperature can improve conductivity by providing enough energy to electrons to overcome the bandgap.
In reality, pure water is a poor conductor due to the lack of free ions. However, the water we typically encounter contains dissolved minerals in the form of ions, thus facilitating electrical conduction.
Metals conduct electricity easily because their atoms have free electrons that can move very easily under the influence of an electric voltage, thus enabling the efficient transport of charges.
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