We know that a current-carrying conductor placed in a magnetic field is exposed to force. Its direction depends on the direction of the field lines of force and the direction of the current: if the latter are known, then the direction of the force can be determined using the rule of the left hand or the right screw.
Let us now consider what the magnitude of this force depends on. Let us turn to the experience.
We hang the linear conductor AB to the left shoulder of the beam arm of the lever balance and place it between the poles N and S of the electromagnet so that it is perpendicular to the magnetic field lines. In series with this conductor, we turn on the ammeter, as well as the rheostat, with which you can measure the current in our conductor. Balance the balance and close the chain. Let the current in conductor AB be directed from B to A. The balance of the balance will be disturbed; in order to restore it, an additional balance will have to be put on the right bowl, the weight of which will be equal to the force acting on the conductor vertically down. We will now change the current in our conductor; we note that with increasing current, the force acting on the conductor also increases. Changes will show us that the force with which a magnetic field acts on a conductor is directly proportional to the current flowing through it.
Does this force depend on the length of the conductor AB? To solve this issue, we will take conductors of different lengths at the same current. The measurements will show us that the force with which the magnetic field acts on the current conductor will be directly proportional to the length of the part of the conductor located in the magnetic field.
Let F be the force that acts on a conductor with a current placed in a magnetic field, l is the length of this conductor and I is the current in it.
As the length of the conductor l and the current in it change, as we have seen, the magnitude of the force F.
The ratio of the force F to the length of the conductor I and to the current in it is a constant value that does not depend on the current in it; therefore, the magnitude of this ratio can characterize the magnetic field.
This value is called magnetic induction or magnetic field induction.
We denote magnetic induction by the letter B. According to the definition, we can write:
B = F / (I · l).
In the SI system, the unit of magnetic induction is the induction of a field in which a conductor with a current of 1 A and a length of 1 m is exposed to a force of 1 N. The name of such a unit is 1 newton / (ammeter) (abbreviated 1 N / (Amm)) .
We show that 1 N / (˖) = 1 (˖) / m²:
1 N / (˖) = 1 (˖) / (˖²) = 1 j / (˖²) = 1 (˖˖) / (˖²) = 1 (˖ sec) / m².
A unit of 1 volt-second is called a weber (wb). Consequently, 1 WB / m² or 1 Tesla (T) is a unit of magnetic induction. Whereas in the GHS measurement system the unit of measurement of magnetic induction is gauss (G):
1 T = 10⁴ G.
Magnetic induction is a vector quantity. The direction of the induction vector at a given point is aligned with the direction of the magnetic line of force passing through this point.
In the SI system, magnetic induction is a force characteristic of a magnetic field, similar to how electric field strength expresses a force characteristic of an electric field.
Knowing the induction of a magnetic field, we can calculate its force acting on a conductor with current, according to the formula:
F = BI l.
In a conductor with current, charges move not only randomly in different directions, but also in a certain direction. Each of the charges is affected by a magnetic force, which is transmitted to the conductor. The sum of all the forces from the chaotic motion is zero, and the sum of the forces of the directed motion is called the Ampere force.
In the general case, the magnitude of the force that acts on a conductor with a current placed in a magnetic field is determined by Ampere's law:
F = BI l sin α, where α is the angle between the directivity of the current (I) and the magnetic field vector (B).
Induction of a magnetic field is numerically equal to the force with which a magnetic field acts on a single current element perpendicular to the induction vector. Magnetic induction depends on the properties of the medium.