No doubt everyone in childhood liked to play with a magnet. It was very simple to get a permanent magnet: to do this, you had to find an old speaker, remove a sound-producing speaker from it and, after simple “vandal actions”, get a ring magnet from it. It is not surprising that many conducted the experiment with metal filings and a sheet of paper. Sawdust was arranged in strips along the lines of field strength.
In electrical engineering, much more widespread are not constants, but electromagnets. From the course of physics it is known that when an electric current flows through a conductor, a magnetic field is created around the latter, the magnitude of which is directly related to the current value.
Doubters can repeat Oersted’s simplest experiment when a compass is placed next to a rectilinear conductor with current. In this case, the arrow will deviate from the geographic north pole of the planet (perpendicular to the wire). The direction of deviation can be determined using the rule of the right hand: place the right hand parallel to the conductor, palm down. 4 fingers should indicate the direction of current. Then the thumb bent 90 degrees will indicate the side of the arrow's deviation. Around a straight wire, the magnetic field looks like a cylinder with a wire in the middle. But tension lines form rings.
In electrical engineering, these magnetic fields are used primarily in coils. Often you can hear the expression "magnetic field of the solenoid." Imagine an ordinary nail and a thin wire in isolation. Evenly winding the wire around the nail, we get a solenoid. In this case, the nail affects the magnetic field of the solenoid, but this is a topic for a completely different article. It is important to understand what exactly is meant by the term. If you now connect the coil to a current source, then a magnetic field will appear around it.
The energy of the magnetic field of the solenoid is directly proportional to the value of the inductance and the square of the current passing through the turns. In turn, the inductance depends on the square of the number of turns. In this case, the design of the winding must be taken into account: this can be a simple case with one layer of turns, as well as a multilayer structure, where the direction of the current in the turns has a corrective effect on the total energy. Solenoids are used in tram schemes, cutting mechanisms, contactors, etc.
The magnetic field of the solenoid is a ring extending from one end of the winding and entering the other. Inside the coil, the lines of force are not interrupted, but propagate in a dielectric medium or along a conductive core. Consequence: the field of the solenoid is polar. The lines exit the magnetic north pole and return to the south. It is easy to guess that the magnetic field of the solenoid depends on the polarity of the current source connected to the ends of the wire. The magnetic properties of the solenoid practically coincide with the permanent magnet. This allows the use of a solenoid as an electromagnet. In production, you can see cranes that have an electromagnet disk instead of a hook. This is the "big brother" of the solenoid - the core winding. The peculiarity of all electromagnets is that magnetic properties exist only when current flows through the turns.
In addition to solenoids, toroids are often used. These are the same turns of wire, but wound around a circular magnetic core. Accordingly, the magnetic field of the solenoid and toroid are different. The main feature is that the lines of force of the magnetic field propagate along the magnetic core inside the coil itself, and not outside it, as in the case of a solenoid. All this indicates a higher efficiency of the coils on the ring magnetically conductive material. Consequence: toroidal transformers are reliable and have less losses than their usual counterparts.