The magnetic field of the solenoid. Electromagnets

No doubt, everyone in childhood liked to play with a magnet. It was very easy to get a permanent magnet: for this purpose it was necessary to find an old column, to extract a sound-reproducing speaker from it and, after simple "vandal actions", to get out of it an annular magnet. Not surprisingly, many conducted an experiment with metal filings and a sheet of paper. The sawdust was located along the lines of tension of the field.

In electrical engineering much more common is not permanent, but electromagnets. It is known from the physics course that when a current flows through a conductor, a magnetic field around the latter is created, the value of which is directly related to the current value of the current.

Doubters can repeat the simplest experience of Oersted when a compass is placed next to a rectilinear conductor with current. In this case, the arrow will deviate from the geographical north pole of the planet (perpendicular to the wire). The direction of the deviation can be determined with the help of the rule of the right hand: place the right hand parallel to the conductor palm downward. 4 fingers must indicate the direction of the current. Then the 90-degree-bent thumb marks the deflection side of the arrow. Around the straight wire, the magnetic field looks like a cylinder with a wire in the middle. But the tension lines form rings.

In electrical engineering, these magnetic fields are used, first of all, in coils. Often one can hear the expression "magnetic field of a solenoid". Imagine an ordinary nail and a thin wire in isolation. Evenly winding the wire on the nail, we get a solenoid. In this case, the nail affects the magnetic field of the solenoid, but this is a completely different topic. It is important to understand what exactly is meant by the term. If now connect the coil to the current source, then around it a magnetic field will arise.

The energy of the magnetic field of the solenoid is directly proportional to the value of the inductance and to 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, it is necessary to take into account the winding design: it can be a simple case with one layer of turns, and also a multilayer structure, where the current direction in the turns has a corrective effect on the total energy. Solenoids are used in the schemes of trams, cutting mechanisms, contactors, etc.

The magnetic field of the solenoid is a ring that emerges from one end of the winding and enters the other. Inside the coil, the lines of force are not interrupted, but propagate in a dielectric medium or along a conducting core. Corollary: the field of the solenoid is polar. The lines exit from the magnetic north pole, and return to the south pole. It is not difficult 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 solenoid to be used as an electromagnet. In production, you can see the cranes, which instead of the hook placed an electromagnet disk. This is the "big brother" of the solenoid - the winding on the core. The peculiarity of all electromagnets is that magnetic properties exist only when the current flows through the turns.

In addition to solenoids, toroids are often used. These are the same turns of wire, but wound on a circular magnetic circuit. Accordingly, the magnetic field of the solenoid and the toroid are different. The main feature is that the lines of force of the magnetic field propagate through 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.