In 1820, the prominent French physicist Andre Marie Ampère (the unit of measurement of electric current was named after him) formulated one of the fundamental laws of all electrical engineering. Subsequently, the name amperage was assigned to this law.
As you know, when an electric current passes through a conductor around it, its own (secondary) magnetic field appears, the intensity lines of which form a kind of rotating shell. The direction of these lines of magnetic induction is determined using the rule of the right hand (the second name is “gimlet rule”): mentally grab the conductor with your right hand so that the flow of charged particles coincides with the direction indicated by the bent thumb. As a result, the other four fingers wrapping around the wire will indicate rotation of the field.
If two such conductors (thin wires) are placed in parallel, then the amperage will affect the interaction of their magnetic fields. Depending on the direction of the current in each conductor, they can be repelled or attracted. At currents flowing in one direction, the ampere force has an attractive effect on them. Accordingly, the opposite direction of the currents causes repulsion. This is not surprising: although the charges of the same name repel, in this example, not the charges themselves interact, but magnetic fields. Since the direction of their rotation coincides, the resulting field is a vector sum, not a difference.
In other words, a magnetic field acts in a certain way on a conductor crossing the lines of tension. Ampere force (arbitrary shape of the conductor) is determined from the formula of the law:
dF = B * I * L * sin a;
where - I is the value of the current strength in the conductor; B — induction of the magnetic field in which the current-conducting material is placed; L - taken for calculating the length of the conductor with current (and, in this case, it is believed that the length of the conductor and the force tend to zero); alpha (a) is the vector angle between the direction of motion of the charged elementary particles and the lines of intensity of the external field. The corollary is as follows: when the angle between the vectors is 90 degrees, its sin = 1, and the value of the force is maximum.
The vector direction of the ampere force is determined by the rule of the left hand: mentally place the palm of the left hand so that the lines (vectors) of the magnetic induction of the external field enter the open palm, and the other four straightened fingers indicate the direction in which the current moves in the conductor. Then the thumb, bent at an angle of 90 degrees, will show the direction of the force acting on the conductor. If the angle between the electric current vector and an arbitrary induction line is too small, then, to simplify the application of the rule, the module should not enter the palm itself, but the module.
The use of amperage made it possible to create electric motors. We are all accustomed to the fact that it is enough to click the switch of an electric household appliance equipped with an engine so that its actuator comes into effect. And no one really thinks about the processes taking place at the same time. The direction of the ampere force not only explains the principle of operation of the engines, but also allows you to determine where exactly the torque will be directed.
For example, imagine a DC motor: its anchor is a frame base with a winding. An external magnetic field is created by special poles. Since the winding wound on the anchor is circular, then from the opposite sides of the current direction in the sections of the conductor is opposite. Consequently, the action vectors of the ampere force are also encountered. Since the anchor is mounted on bearings, the mutual action of the ampere force vectors creates a torque. With an increase in the effective value of the current, the force also increases. That is why the rated electric current (indicated in the passport for electrical equipment) and torque are directly interconnected. The increase in current is limited by design features: the cross section used for winding the wire, the number of turns, etc.