Anyone who has chosen electrical engineering as his main profession is very well aware of some of the basic properties of electric current and the accompanying magnetic fields. One of the most important of them is the rule of the gimlet. On the one hand, it is rather difficult to call this rule a law. It is more correct to say that this is one of the fundamental properties of electromagnetism.
What is a gimlet rule? The definition, although it exists, but for a more complete understanding it is worth recalling the basics of electricity. As you know from the school physics course, electric current is the movement of elementary particles carrying an electric charge through some conductive material. Usually it is compared with the interatomic movement of valence electrons, which due to external action (for example, a magnetic pulse) receive a portion of energy sufficient to leave their steady-state orbit in the atom. Let's do a thought experiment. To do this, we need a load, an emf source and a conductor (wire) that connects all the elements into a single closed circuit.
The source creates a directed motion of elementary particles in the conductor. Moreover, as early as the 19th century, it was noticed that a magnetic field appears around such a conductor , which rotates in one direction or another. The rule of the gimlet just allows you to determine the direction of rotation. The spatial configuration of the field is a kind of tube, in the center of which is a conductor. It would seem: what a difference, how this generated magnetic field behaves! However, Ampere also noticed that two conductors with current act on each other with their magnetic fields, repelling or attracting to each other, depending on the direction of rotation of their fields. Subsequently, based on a number of experiments, Ampère formulated and substantiated his law of interaction (by the way, it underlies the operation of electric motors). Obviously, without knowing the rule of the gimlet, it is very difficult to understand the ongoing processes.
In our example, the direction of the current is known - from "+" to "-". Knowing the direction makes it easy to use the gimlet rule. Mentally, we begin to screw a gimlet with a standard right-hand thread into the conductor (along it) so that the resulting translational motion is coaxial with the direction of current flow. In this case, the rotation of the handle will coincide with the rotation of the magnetic field. You can use another example: we screw in a regular screw (bolt, screw).
The indicated rule can be used in a slightly different way (although the main meaning is the same): if you mentally grab the current conductor with your right hand so that four bent fingers indicate the direction in which the field rotates, then the bent thumb will indicate the direction of the current flowing through the conductor . Accordingly, the opposite is also true: knowing the direction of the current, "grabbing" the wire, you can find out the direction of the rotation vector of the generated magnetic field. This rule is actively used in the calculation of inductors, in which, depending on the direction of the turns, it is possible to influence the flowing current (creating, if necessary, a countercurrent).
The law of the gimlet allows us to formulate the corollary: if the right palm is placed in such a way that the lines of intensity of the generated magnetic field enter it, and four straightened fingers indicate the known direction of motion of the charged particles in the conductor, then the thumb bent at an angle of 90 degrees will indicate the direction of the vector the force exerting a biasing effect on the conductor. By the way, it is this force that creates the torque on the shaft of any electric motor.
As you can see, there are a lot of ways to use the above rule, so the main “complexity” is the selection by each person of what is understandable to him.