In electricity, three main groups of materials are distinguished - these are conductors, semiconductors and dielectrics. Their main difference is the ability to conduct current. In this article, we will look at how these types of materials differ and how they behave in an electric field.
Content:
- What is a conductor
- What is a dielectric
- What is a semiconductor
- Zone theory
What is a conductor
A substance in which free charge carriers are present is called a conductor. The motion of free carriers is called thermal. The main characteristic of a conductor is its resistance (R) or conductivity (G) - the reciprocal of resistance.
G = 1 / R
In simple terms, a conductor conducts current.
These substances include metals, but if we talk about non-metals, then, for example, carbon is an excellent conductor, has found application in sliding contacts, for example, in an electric motor brush. Wet soil, solutions of salts and acids in water, the human body also conduct current, but their electrical conductivity is often less than that of copper or aluminum, for example.
Metals are excellent conductors due to the large number of free charge carriers in their structure. Under the influence of an electric field, the charges begin to move, and also redistribute, the phenomenon of electrostatic induction is observed.
What is a dielectric
Dielectrics are substances that do not conduct current, or conduct, but very poorly. They have no free charge carriers, because the bond between the particles of the atom is strong enough for formation of free carriers, therefore, under the influence of an electric field, the current in the dielectric does not arises.
Gas, glass, ceramics, porcelain, some resins, textolite, carbolite, distilled water, dry wood, rubber are dielectrics and do not conduct electric current. In everyday life, dielectrics are ubiquitous, for example, they are used to make cases for electrical appliances, electrical switches, cases for plugs, sockets, and so on. In power lines, insulators are made of dielectrics.
However, in the presence of certain factors, for example, an increased level of humidity, the electric field strength is higher permissible value and so on - lead to the fact that the material begins to lose its dielectric functions and becomes conductor. Sometimes you can hear phrases like "breakdown of the insulator" - this is the phenomenon described above.
In short, the main properties of a dielectric in the field of electricity are electrical insulating. It is the ability to prevent the flow of current that protects a person from electrical injuries and other troubles. The main characteristic of a dielectric is its dielectric strength - a value equal to its breakdown voltage.
What is a semiconductor
A semiconductor conducts an electric current, but not like metals, but under certain conditions - the communication of energy to the substance in the required quantities. This is due to the fact that there are too few or no free charge carriers (holes and electrons), but if you apply a certain amount of energy, they will appear. Energy can be of various forms - electrical, thermal. Also, free holes and electrons in a semiconductor can arise under the influence of radiation, for example, in the UV spectrum.
Where are semiconductors used? They are used to make transistors, thyristors, diodes, microcircuits, LEDs, and more. Such materials include silicon, germanium, mixtures of different materials, for example, gallium arsenide, selenium, arsenic.
To understand why a semiconductor conducts electric current, but not like metals, you need to consider these materials from the point of view of band theory.
Zone theory
Band theory describes the presence or absence of free charge carriers relative to certain energy layers. The energy level or layer is called the amount of energy of electrons (nuclei of atoms, molecules - simple particles), they are measured in terms of Electron volts (EV).
The image below shows three types of materials with their energy levels:
Note that in the conductor, the energy levels from the valence band to the conduction band are combined into an unbreakable diagram. The conduction band and the valence band overlap, this is called the overlap band. Depending on the presence of an electric field (voltage), temperature, and other factors, the number of electrons may change. Thanks to the above, electrons can move in conductors, even if they are given some minimal amount of energy.
A semiconductor has a certain forbidden value between the valence band and the conduction band. The band gap describes how much energy needs to be imparted to the semiconductor in order for the current to flow.
For a dielectric, the diagram is similar to the one that describes semiconductors, but the difference is only in the band gap - it is many times large here. The differences are due to the internal structure and substance.
We looked at the main three types of materials and gave their examples and features. Their main difference is the ability to conduct current. Therefore, each of them has found its own field of application: conductors are used to transmit electricity, dielectrics - to insulate live parts, semiconductors - for electronics. We hope the information provided has helped you understand what conductors, semiconductors and dielectrics are in an electric field, as well as what is their difference.
Finally, we recommend watching a useful video on the topic:
You probably don't know:
- Causes of power loss over long distances
- The dependence of the resistance of the conductor on temperature
- What is dielectric loss
- What is electric charge
