Actions of electric current: thermal, chemical, magnetic, light and mechanical

Electric current in a circuit always manifests itself through some kind of its action. This can be both operation at a certain load and the concomitant effect of the current. Thus, by the action of the current, its presence or absence in a given circuit can be judged: if the load is working, there is current. If a typical phenomenon accompanying the current is observed, there is a current in the circuit, etc.

In principle, electric current is able to cause different actions: thermal, chemical, magnetic (electromagnetic), light or mechanical, and different types of current actions often occur simultaneously. These current phenomena and actions will be discussed in this article.

Thermal effect of electric current

When direct or alternating current flows through a wire, the wire heats up. Such heating wires under different conditions and applications can be: metals, electrolytes, plasma, molten metals, semiconductors, semimetals.

In the simplest case, if, say, an electric current passes through a nichrome wire, it will heat up. This phenomenon is used in heating devices: in electric kettles, in boilers, in heaters, electric stoves, etc. In electric arc welding, the temperature of the electric arc usually reaches 7000 ° C, and the metal melts easily, this is also a heat effect of the current.

The amount of heat released in the section of the circuit depends on the voltage applied to this section, the value of the current flowing and the time of its flow (The Joule-Lenz law).

Once you have converted Ohm's law for a section of circuit, you can use either voltage or current to calculate the amount of heat, but then you must know the resistance of the circuit because it limits current and actually causes heating. Or, knowing the current and voltage in a circuit, you can just as easily find the amount of heat generated.

Chemical action of electric current

Electrolytes containing ions by direct electric current electrolyzed — this is the chemical action of the current. Negative ions (anions) are attracted to the positive electrode (anode) during electrolysis, and positive ions (cations) are attracted to the negative electrode (cathode). That is, the substances contained in the electrolyte are released during electrolysis at the electrodes of the current source.

For example, a pair of electrodes is immersed in a solution of a certain acid, alkali, or salt, and when an electric current passes through the circuit, a positive charge is created on one electrode and a negative charge on the other. The ions contained in the solution begin to deposit on the electrode with a reverse charge.

For example, during the electrolysis of copper sulfate (CuSO4), copper cations Cu2 + with a positive charge move to the negatively charged cathode, where they receive the missing charge, and turn into neutral copper atoms, settling on the surface of the electrode. The hydroxyl group -OH will donate electrons to the anode and oxygen will be released as a result. The positively charged hydrogen cations H + and the negatively charged SO42- anions will remain in solution.

The chemical action of an electric current is used in industry, for example, to break down water into its component parts (hydrogen and oxygen). Also, electrolysis allows you to get some metals in their pure form. With the help of electrolysis, a thin layer of a certain metal (nickel, chromium) is applied to the surface — that's it galvanic coating etc.

In 1832, Michael Faraday established that the mass m of the substance released at the electrode is directly proportional to the electric charge q that passed through the electrolyte. If a direct current I flows through the electrolyte for time t, then Faraday's first law of electrolysis applies:

Here the proportionality factor k is called the electrochemical equivalent of the substance. It is numerically equal to the mass of a substance released when an electric charge passes through the electrolyte, and depends on the chemical nature of the substance.

Magnetic action of electric current

In the presence of an electric current in any conductor (in a solid, liquid or gaseous state), a magnetic field is observed around the conductor, that is, the current-carrying conductor acquires magnetic properties.

So if a magnet is brought to the wire through which the current flows, for example in the form of a magnetic compass needle, then the needle will turn perpendicular to the wire, and if you wind the wire on an iron core and pass a direct current through the wire, the core will become electromagnet.

In 1820, Oersted discovered the magnetic effect of current on a magnetic needle, and Ampere established the quantitative laws of the magnetic interaction of current-carrying wires.

The magnetic field is always generated by current, that is, moving electric charges, in particular — charged particles (electrons, ions). Opposite currents repel each other, unidirectional currents attract each other.

Such a mechanical interaction occurs due to the interaction of magnetic fields of currents, that is, it is first of all a magnetic interaction, and only then - mechanical. Thus, the magnetic interaction of the currents is primary.

In 1831, Faraday found that a changing magnetic field from one circuit generates a current in another circuit: the EMF generated is proportional to the rate of change of the magnetic flux. It is logical that it is the magnetic action of currents that is used to this day in all transformers, not only in electromagnets (for example, in industrial ones).

Light effect of electric current

In its simplest form, the luminous effect of an electric current can be observed in an incandescent lamp, the coil of which is heated by the current passing through it to white heat and emits light.

For an incandescent lamp, the light energy represents about 5% of the electricity delivered, the remaining 95% of which is converted into heat.

Fluorescent lamps more efficiently convert current energy into light — up to 20% of electricity is converted into visible light thanks to phosphors that receive ultraviolet radiation from an electric discharge in mercury vapor or in an inert gas such as neon.

The light effect of electric current is realized more effectively in LEDs. When an electric current passes through the pn junction in the forward direction, the charge carriers—electrons and holes—recombine with the emission of photons (due to the transition of electrons from one energy level to another).

The best light emitters are direct-gap semiconductors (that is, those in which direct optical transitions are allowed), such as GaAs, InP, ZnSe, or CdTe. By changing the composition of the semiconductors, LEDs can be made for all kinds of wavelengths from ultraviolet (GaN) to mid-infrared (PbS). The efficiency of the LED as a light source reaches an average of 50%.

Mechanical action of electric current

As noted above, any conductor through which an electric current flows forms around itself magnetic field… Magnetic actions are converted into motion, for example in electric motors, in magnetic lifting devices, in magnetic valves, in relays, etc.

The mechanical action of one current on another is described by Ampere's law. This law was first established by Andre Marie Ampere in 1820 for direct current. From Ampere's Law it follows that parallel wires with electric currents flowing in one direction attract and those in opposite directions repel.

Ampere's law is also called the law that determines the force with which a magnetic field acts on a small segment of a current-carrying conductor. The force with which a magnetic field acts on an element of a current-carrying wire in a magnetic field is directly proportional to the current in the wire and the element vector product of the length of the wire and the magnetic induction.

This principle is based on operation of electric motors, where the rotor plays the role of a frame with a current oriented in the external magnetic field of the stator by the torque M.