Regarding the conduction of metal conductors, the classical conduction theory believes that there are a large number of free electrons that can move freely inside the metal conductor. These free electrons move directionally under the action of the electric field force to form an electric current.
1 Extranuclear electron of metal atoms
All atoms are composed of the nucleus and the extranuclear electrons moving around the nucleus. The centripetal force required for the movement of the electrons outside the nucleus is provided by the Coulomb electric field force between the nucleus and the electrons. Numerous extranuclear electrons are at different distances from the nucleus outside the nucleus. The electron closest to the nucleus has the greatest force and the total energy of the electron is the lowest. The outermost electron farthest from the nucleus has the least binding force by the nucleus, the electron’s potential energy is the largest, and the total energy is the largest. . Because the outermost electron is the least bound, it is often interfered with by neighboring atoms and moves around the neighboring nuclei. The metal atoms are combined into a metal body based on the force formed by the mutual winding motion after the interference of the outer layer of electrons. Due to the very small binding force, the metal has the characteristics of softness and easy deformation when heated.
2 Metal conductor under the action of Lorentz force (or induced electric field force)
If a metal conductor cuts the magnetic line of induction in a magnetic field, the electrons outside the core inside the conductor will be subjected to the Lorentz force, and the atoms will be polarized under this action, resulting in an atomic polarization electromotive force. But no matter how great the Lorentz force is, it cannot do work on the electron, increase the kinetic energy of the electron, and make it free from the bond of the nucleus. After the electron is free from the bond of the nucleus, it will continue to work on it, and it will accelerate in the direction of the force to form an electric current.
3 Metal conductors under voltage distribution and electric field force
If a voltage is applied to both ends of a metal conductor to form a voltage distribution electric field inside the conductor, the electrons in the outer nuclear layer inside the conductor should be subjected to the voltage distribution electric field force when they move around the nucleus, and the electric field force does positive work on the electrons. , To increase the kinetic energy of the electrons, and have enough energy to overcome the bondage of the nucleus, and become free electrons outside the nucleus. Because only the outermost electrons in the outer nucleus have the largest energy, to form free electrons, it is necessary to overcome the nuclear gravity and do the least work, so Under normal circumstances, when a voltage is applied to both ends of a conductor, only the outermost electrons can leave the nucleus and become free electrons. The outermost electron needs to do the least work to break away from the bondage of the nucleus. The free electrons after forming a current are actually not free. On the one hand, they are affected by the electric field force of the voltage distribution and movement in the direction of the electric field force. On the other hand, they are not unimpeded during the movement. For a very tiny electron, the space inside and outside the atom can be said to be quite expansive. The nucleus is like a star in cosmic space, while free electrons are like a small meteor flying in cosmic space. This analogy is not very appropriate, because Meteor flying in space may not cause resistance from other objects, but free electrons are subject to resistance. This is because the space outside the nucleus is not without nothing but also orbits the inner electrons, and these metals The number of inner electrons is much more than the outermost electrons that form free electrons. We might as well call the barrier formed by the inner electrons of these atoms as electron cloud gas. The electron cloud gas is negatively charged, and the free electrons are also negatively charged. Therefore, if free electrons shuttle in the electron cloud gas to form an electric current, it is bound to be resisted by the electron cloud gas. After the stable current is formed, if the voltage at both ends of the conductor is suddenly removed, the electric field inside the conductor disappears, and the free electrons lose the effect of the electric field force. Only resistance acts on it, so the electrons decelerate and the speed quickly decreases to zero. . Then, under the action of the gravitational force of the nucleus, it returns to the corresponding orbit of the outer layer of the nucleus to move around the nucleus.
4 Ohm's law and resistance law
In the process of current flow, due to the resistance of the electron cloud gas to free electrons, it forms a certain obstacle to the flow of current, which also produces the resistance of the conductor. It must be noted that the resistance of free electrons during movement is not equal to the resistance of the conductor. The resistance of free electrons does not mean that the resistance of the conductor is large. Conversely, the resistance of the conductor is large, which does not mean that the resistance of the conductor is large. When moving in a directional direction, the resistance is great.
5 Energy Conversion and Joule's Law
When voltage is just applied to both ends of the conductor, the electric field force does positive work on the outermost electrons of the nucleus to overcome the binding force of the nucleus, but the work done by the electric field force overcoming the binding force of the nucleus is far less than the work done by the long-term current flow to overcome the resistance of the electron cloud. Therefore, the work done to overcome the bondage of the nucleus is very small and can be ignored.
During the acceleration of free electrons, the electric field force also does positive work to it, but because the electron has a very short acceleration time and the movement displacement is very small (not discussed here), the electric field force is also very small and can be ignored. Therefore, after the free electrons form a current, the main energy loss of the electric field is to overcome the electron cloud to do work.
6 The energized conductor moves in a magnetic field
In the above analysis, when the current passes through the conductor, it only overcomes the electron cloud gas to do work. The obstacle of the electron cloud gas to free electrons is shown as resistance, so such a conductor is called a pure resistance conductor, and a circuit with only a pure resistance conductor in the circuit is called a pure resistance circuit. It can be seen from the above formulas that the pure resistance circuit converts electrical work into heat energy.
However, the energized conductor will be subjected to the force of the magnetic field (ampere force) in the magnetic field. Under this force, the conductor starts to move faster, cutting the magnetic lines of induction, polarizing the atoms in the conductor, and generating a polarized electromotive force. The formation of terminal induced electromotive force will generate an electric field in other parts of the outer conductor, and produce resistance to the free electrons flowing through. In order to overcome the resistance, the current generates a voltage distribution electric field in the same direction as the current in the conductor, making the electric field and the induction The electric field generated by the electromotive force cancels out, thus maintaining the stability of the current, and also generates a voltage at both ends of the conductor. The magnitude of the voltage is exactly the same as the induced electromotive force and the direction is opposite.
In this way, the voltage distribution electric field force must overcome the resistance generated by the induced electromotive force to do work and consume electric energy. This energy is converted into an ampere force to do work on the outside world, which appears in the form of mechanical energy.
If the conductor placed in the magnetic field is not an ideal conductor, then the electric field force must not only overcome the induced electromotive force to do work but also overcome the resistance of the electron cloud to do work. Therefore, part of the electrical energy is converted into the form of mechanical energy, and part of it is converted into heat energy.
7 Power supply after current flow
What happens inside the power supply after the current flows? Since non-electrostatic force can only polarize atoms and generate electromotive force in the power supply, the non-electrostatic force cannot do work on electrons, nor can it make outer electrons overcome the bondage of atomic nuclei and become free electrons, let alone direct movement of electrons to form an electric current. , Then, how is the current inside the power supply formed?
To form a current in the power supply, in addition to making the outer electrons overcome the bondage of the nucleus, it is also necessary to overcome the resistance of the electron cloud to perform work. Non-electrostatics have no such function. Therefore, a voltage distribution from the negative pole of the power supply to the positive pole must be generated in the power supply. In the electric field, the outer layer of electrons forms a current under the action of this electric field force and generates a voltage drop inside the power supply. The voltage drop is higher than the positive electrode potential, that is, the direction is from the negative electrode to the positive electrode, and the direction of the electromotive force of the power supply is opposite.
