The higher the temperature, the more violent the irregular movement of atoms in the conductor, the greater the obstruction effect on free electrons, so most of the materials with the increase of temperature, the resistivity will also increase; However, there are some semiconductor materials, when the temperature is properly increased, the number of free electrons will be greatly increased, at this time, the temperature is increased, the resistivity of the material is reduced.

In the conductor, when the free electron moves in a directional way, it will collide with other particles, and it will also be affected by the positively charged nucleus, resulting in the loss of kinetic energy of the free electron, and the lost kinetic energy will be converted into the irregular motion of other particles, that is, the internal energy of the conductor itself, from a macro point of view, the conductor also has resistance.

According to this microscopic principle, it is easy to understand the resistivity, the resistivity ρ : indicates the physical quantity of the conductive property of the object, the material resistance R=ρL/S.

Material length L: The longer the conductor material, the more the directional moving charge is hindered, so the resistance is proportional to the length of the material.

Material cross-sectional area S: The larger the cross-sectional area of the material, the greater the number of free electrons in the conductor per unit length, and the better the conductivity of the conductor.

Temperature: Temperature will affect the microscopic properties of the material, and will affect the conductive properties of the conductor to a certain extent.

Among all materials, the outer electrons of metals tend to break away, so the free electrons in metals are relatively more, and the electrical conductivity is better than that of other materials.

It should be noted that the directional motion of free electrons is very slow, only a few millimeters to a few centimeters per second, but the electric field travels close to the speed of light in the conductor, and the propagation speed of the current depends on the electric field speed.

For solid materials, the directional movement of free electrons forms a current, and because there are positive and negative charges in the solid at the same time, the directional movement of free electrons will be hindered, which is the microscopic principle of resistance.

The essence of current is the directional movement of charge, substance is composed of atoms, atoms are composed of positively charged nuclei and negative electrons of the extranuclear electrons, in the conductor material, part of the extranuclear electrons from the bondage of the nucleus to become free electrons, if the electric field is added at both ends of the conductor, the free electrons in the conductor will produce directional movement, also produced current.