In addition to the Coulomb electric potential, there is a vortex field, which has closed the line tension. Knowing the General properties of the electric field, it is easier to understand the nature of the vortex. It is generated by a changing magnetic field.
What causes the induced current of the conductor being stationary? What is the induction electric field? The answer to these questions, as well as about the difference between a vortex and a stationary electrostatic, eddy currents, ferrite, and the more you will learn from the following article.
How does the magnetic flux change
Magnetic flux f=BSosɑ may be changed in contour in two variants: stationary loop in changing field, and in a state of motion in the field, fixed or variable. An electromotive induction force in both cases is to obey one law, but will happen in different ways.
Occurrence of induction current and charge driving force
You must first understand how an induction current. For the round coil of wire placed in a magnetic homogeneous body. If the induction in it will increase, that will be followed by the magnetic flux through the surface. Following this, there is a current. If the magnetic field will change according to the linear law, the current will remain constant.
The question is that for the forces begin to move the charges in the coil. The magnetic field in the coil is not capable of this, because it affects only moving charges. But the conductor in it remains motionless!
The charges are affected by electric field. But the stationary and electrostatic charges are formed, and the induction current in response to changing magnetic field!
It would be logical to assume that the electron starts moving electric field, parodys the result of the changing magnetic field. So, physicist Maskwell came to the conclusion that the magnetic field over time, gives rise to electric.
Then, electromagnetic induction is shown in a new way, where the main feature appears to be the product of electric field magnetic. Conductive circuits does not change anything. A conductor with free electrons becomes an instrument, allowing to identify emerging electric field, due to the fact that it moves in the conductor. Electromagnetic induction conductor, which is stationary, is not only the appearance of the induced current, and the electric field starting movement of electric charges.
Vortex electric field appeared behind magnetic, is of a different kind than electrostatic. It has no direct connection with the charges, and tension on its lines begin and end. This is a closed line, like the magnetic field. Therefore, it is called vortex electric field.
Magnetic induction will change faster, the greater the tension. Lenz's law States: when increasing the magnetic induction the direction of the intensity vector of the electric field creates a left-hand screw direction of the other vector. That is, when the rotation of the left screw in the direction of lines of tension its forward movement will be the same as that of the magnetic induction vector.
If the magnetic induction decreases, then the direction of the intensity vector will create a right screw with the direction of another vector.
The lines of force of the tension have the same direction as the induction current. Vortex electric field acts on a charge with the same force as before. However, in this case his work on the moving charge is different from zero, in stationary electric field. Because the force and displacement have the same direction, and work throughout the ways the closed lines of tension will be the same. Work unit positive charge here is equal to the electromotive force of induction in the conductor.
Induction currents in massive conductors
In massive conductors, induction currents receive maximum values. This is because they have little resistance.
These currents are called Foucault currents (this is a French physicist who studied them). They can be used to change the temperature of the conductors. This principle lies in the induction furnaces, for example, domestic microwave. It is also used for melting metals. Electromagnetic induction is used in metal detectors placed in airports, theaters and other public places with the accumulation of a large number of people.
But eddy currents lead to energy losses to generate heat. Therefore, cores of transformers, electric motors, generators and other devices made of iron not solid, but from different plates, which from each other isolated. The plates should be strictly perpendicular relative to the intensity vector, which has a vortex electric field. Plates then will have a maximum resistance to current, and heat will be allocated a minimum amount.
Radio equipment operates at the highest frequencies, where the number reaches millions of oscillations per second. The coils of the cores will not be effective here, since the Foucault currents will appear in each plate.
There are insulators magnets called ferrites. Eddy currents in them will not appear during the magnetization reversal. Therefore energy losses to heat are reduced to a minimum. They are made from the cores used for high frequency transformers, antenna, transistor and so on. They are prepared from mixtures of the initial substances, which are pressed and treated with heat by.
If the magnetic field in the ferromagnet changing rapidly, this leads to induction currents. Their magnetic field will prevent the change of the magnetic flux in the core. Therefore, the flow will not change, and the core — peremagnichivaniya. Eddy currents in ferrites are so small that they can quickly peremagnichivaniya.