The phenomenon of mutual induction is the basis of many electrical appliances. A situation is not uncommon when a person directly encounters its manifestations in everyday life, but does not even suspect it. Let us recall the recent past, when the main means of transmitting information were analog signals. And now, now almost all electronic equipment has been converted to digital modulations. Everyone knows that the “figure” is better. But you wondered what exactly? Surely, some houses still have a wired telephone serviced by an analog telephone exchange. If we compare modern "mobile phones" and "oldies", then the comparison is clearly not in favor of the latter. To hear intermittent broadcasting against the background of your conversation or, what is even “better”, the words of someone else's communication, this will not surprise anyone. This is because all the wires in the telephone cable are close to each other, so mutual induction arises in two lines. Another example is the pulsating clicks that appear in the TV speakers or computer speakers when a cellphone is nearby and a call is ringing to it. Finally, the old IDE loops with 80 conductors used only half of them, while the other 40 prevented the consequences of mutual induction. There are many examples; there is no point in giving everything. It is only important to remember that in this case, any "pick-ups" - this is mutual induction.
In general, this term refers to the process of the appearance of an electromotive force (EMF) in one of the adjacent conductors at a time when the effective current value changes in the other. The most simple mutual induction is explained using a transformer. In a simplified form (a special case), the transformer consists of two coils wound on the same magnetic circuit. When current flows through the wire of one of them, a magnetic field arises around . As a result, the magnetic flux that has appeared permeates the conductor of the second coil, creating an EMF in it. In order for an induced current to appear, it is enough to short the terminals of this coil, creating a circuit. With increasing magnetic flux intensity, mutual induction also increases. To achieve the required characteristics (for example, efficiency), various solutions are used: change the configuration of the magnetic circuit; Coils are winded in a special way, etc. The mutual inductance is measured using variometers.
How does it appear in the examples indicated at the beginning of the article? Very simple: in almost all cases (except the cell phone) several conductors are located nearby, at least one of which carries an electric current. Consequently, a magnetic field arises generating magnetic flux. The latter, penetrating nearby conductors, induces an EMF in them, and since there is a circuit, then, in accordance with the law of electromagnetic induction, a current appears. Its orientation is determined by applying the Lenz rule.
Mutual induction is widely used in modern electrical engineering. Since some of its undesirable manifestations were indicated at the beginning of the article, it makes sense to give examples of useful ones. One of the most famous devices is a household voltage stabilizer. Inside there is a transformer (usually a toroidal type) with many terminals, each of which corresponds to a certain voltage value. Also in some devices you can find an interesting solution - galvanic isolation. In fact, this is the same transformer (sometimes an optocoupler pair), but not using a transformation coefficient. As a result, it is possible to carry out the connection of several circuits through the magnetic flux, ensuring the proper level of electrical safety. In production, for example, this is a beam crane.