Thermal action of the current: the Joule-Lenz law, examples

Moving in any conductor, the electric current transfers to it some energy, because of what the conductor heats up. Energy transfer is carried out at the level of molecules: as a result of the interaction of current electrons with ions or atoms of a conductor, part of the energy remains in the latter.

The thermal action of the current leads to a faster movement of the particles of the conductor. Then its internal energy increases and transforms into thermal energy.

The calculation formula and its elements

The thermal action of the current can be confirmed by various experiments, where the work of the current transforms into internal conductive energy. The latter increases. Then the conductor gives it to the surrounding bodies, that is, heat transfer occurs with the heating of the conductor.

The formula for calculating in this case is as follows: A = U * I * t.

The quantity of heat can be denoted by Q. Then Q = A or Q = U * I * t. Knowing that U = IR, we obtain Q = I * R * t, which was formulated in the law of Joule-Lenz.

The law of thermal action of a current - the law of Joule-Lenz

The conductor, where an electric current flows , was studied by many scientists. However, the most notable results were achieved by James Joule from England and Emilia Khristianovich Lents from Russia. Both scientists worked separately and deduced the results of the experiments independently of each other.

They derived a law that allows us to estimate the heat received as a result of the action of the current on the conductor. It was called the law of Joule-Lenz.

Let us consider in practice the thermal action of a current. Let's take the following examples:

1. The usual light bulb.
2. Heating devices.
3. A fuse in the apartment.
4. The electric arc.

Incandescent light bulb

The thermal action of the current and the discovery of the law contributed to the development of electrical engineering and increased opportunities for the use of electricity. The way in which the results of research are applied can be considered by the example of a conventional incandescent bulb.

It is designed in such a way that a thread made of tungsten wire is pulled inside. This metal is refractory with high specific resistance. When passing through a light bulb, the thermal effect of the electric current is realized.

The energy of the conductor is transformed into a thermal one, the helix heats up and starts to glow. The disadvantage of a light bulb is a large energy loss, because only at the expense of a small part of the energy it starts to glow. The main part just heats up.

To better understand this, a coefficient of efficiency is introduced , which demonstrates the efficiency of work and conversion to electricity. The efficiency and thermal action of the current are used in different areas, since there are many devices manufactured based on this principle. Mostly these are heating appliances, electric cookers, boilers and other similar devices.

The device of heating devices

Usually in the design of all appliances for heating there is a metal spiral, the function of which includes heating. If water is heated, then the spiral is installed in an isolated manner, and in such devices a balance is made between the energy from the network and the heat exchange.

Scientists are constantly faced with the task of reducing energy losses and finding the best ways and the most effective schemes for their implementation in order to reduce the thermal effect of the current. For example, a method is used to increase the voltage during the transmission of energy, thereby reducing the amperage. But this method, at the same time, lowers the security of the operation of power lines.

Another research direction is the choice of wires. After all, heat losses and other indicators depend on their properties. In addition, with the operation of heating devices, a large energy release occurs. Therefore, the spirals are made of materials specially designed for these purposes, capable of withstanding high loads.

Apartment fuses

To improve protection and secure electric circuits, special fuses are used. In the role of the main part is a wire made of low-melting metal. It passes in a cork of porcelain, has a screw thread and contact in the center. The plug is inserted into a cartridge located in a porcelain box.

Lead wire is part of the general chain. If the thermal action of the electric current increases sharply, the conductor cross section will not withstand, and it will begin to melt. As a result, the network will open, and no current overload will occur.

Electric arc

The electric arc is a fairly effective converter of electrical energy. It is used for welding metal structures, and also serves as a powerful light source.

The basis of the device is as follows. Take two coal rods, connect the wires and attach them to the insulating holders. After that, the rods are connected to a current source, which gives a small voltage, but is designed for a high current strength. Connect the rheostat. Coals in the city network are prohibited, as this can cause a fire. If you touch one coal on another, you can see how much they will burn. It is better not to look at this flame, because it is harmful to vision. The electric arc is used in furnaces for melting metal, and also in such powerful lighting devices as spotlights, film projectors and so on.