Properties of conductors, semiconductors and insulators

E.CLASSIFICATION OF MATERIALS according to their electrical conductivity



The human body is a poor conductor, but electric current can still flow through it. There is a particular danger if the voltage is (significantly) greater than the low voltage (over 48 volts). Electric current through the human body (also in animals, of course) can be fatal due to the chemical decomposition of the blood (gas development - embolism), due to the thermal destruction of the muscles, or due to the physiological effect on the cells and muscles (muscle spasms combined with respiratory paralysis). The 50 Hertz network frequency has a particular influence. This can lead to ventricular fibrillation with fatal consequences.


Materials can be divided into conductors, semiconductors and non-conductors according to their ability to conduct electricity.


Metals, coal and molten salts (including heated glass) conduct electricity. They are electrical conductors.


Liquids can be both electrical conductors and non-conductors. For example, aqueous solutions of acids, salts and bases are electrical conductors. If distilled water is not contaminated, it will not conduct electricity. It is a non-conductor (insulator) just like acid-free oils.


In the "normal state" gases are non-conductors. At low pressure and high electric field strengths, however, they can become conductive (neon tubes).


Glass, porcelain, rubber, wool, amber and pure silk do not conduct electricity. They are non-conductors and are also known as insulators.


Solid bodies made of silicon and germanium are the basis for the electronics industry. In terms of their management mechanisms, they behave differently from metals. They are neither good conductors nor good insulators at room temperature. They are therefore called semiconductors.

Semiconductors are insulators at very low temperatures. At higher temperatures they become relatively good conductors. Their temperature coefficient is negative. They are therefore called NTC resistors.

The resistance of a semiconductor material decreases when the temperature increases. They are used as thermistors.


All statements about the electrical behavior of substances are only possible for a limited range of temperature, electrical field strength, magnetic field strength, electromagnetic radiation (e.g. light) and aging. Physical and chemical influences can change the conductive properties of a substance temporarily and permanently. Under the influence of electrical current, however, the chemical and physical properties of a substance can change, temporarily or permanently.

The ability of a material to conduct electricity is called specific electrical conductivity.

The ability of a material not to conduct electricity is called specific resistance.

A high electrical conductivity means a small resistance. A large resistance means a small electrical conductivity.

From the diagram you can read off the order of magnitude of the electrical conductivity or the specific resistance of various materials.


Pay attention to the distinction between the terms Conductance and conductivity. The term conductance is component-related, the term conductivity is material-related. That is why one often speaks of the specific conductivity.