Moving in any conductor, an electric current transfers some energy to it, due to which 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 the conductor, part of the energy remains with the latter.
The thermal effect of the current leads to a faster movement of the conductor particles. Then it increases and transforms into heat.
Calculation formula and its elements
The thermal effect of the current can be confirmed by various experiments, where the work of the current is converted into internal conductor energy. At the same time, the latter increases. Then the conductor gives it to the surrounding bodies, that is, heat transfer is carried out with heating of the conductor.
The formula for calculation in this case is as follows: A=U*I*t.
The amount of heat can be denoted by Q. Then Q=A or Q=U*I*t. Knowing that U=IR, it turns out Q=I*R*t, which was formulated in the Joule-Lenz law.
The law of the thermal action of the current is the Joule-Lenz law
The conductor where the flows have been studied by many scientists. However, the most notable results were achieved from England and Emil Khristianovich Lenz from Russia. Both scientists worked separately and conclusions based on the results of the experiments were made independently of each other.
They derived a law that makes it possible to estimate the heat obtained as a result of the action of current on a conductor. It is called the Joule-Lenz law.
Consider in practice the thermal effect of the current. Let's take the following examples:
- Ordinary light bulb.
- Heating appliances.
- fuse in the apartment.
- Electric arc.
Incandescent light bulb
The thermal effect of current and the discovery of the law contributed to the development of electrical engineering and an increase in the possibilities for using electricity. How the research results are applied can be seen in the example of a conventional incandescent light bulb.
It is designed in such a way that a thread made of tungsten wire is pulled inside. This metal is refractory with high resistivity. When passing through a light bulb, the thermal effect of an electric current is carried out.
The energy of the conductor is transformed into heat, the spiral heats up and begins to glow. The disadvantage of the light bulb lies in the large energy losses, since it begins to glow only due to a small part of the energy. The main part just heats up.
To better understand this, it is introduced which demonstrates the efficiency of operation and conversion into electricity. The efficiency and thermal effect of the current are used in different areas, since there are many devices made on the basis of this principle. To a greater extent, these are heating devices, electric stoves, boilers and other similar devices.
The device of heating devices
Usually, in the design of all heating devices there is a metal spiral, the function of which is heating. If water is heated, then the spiral is installed in isolation, and such devices provide for a balance between energy from the network and heat exchange.
Scientists are constantly faced with the task of reducing energy losses and finding the best ways and most efficient schemes for their implementation in order to reduce the thermal effect of the current. For example, a method of increasing the voltage during the time is used, due to which the current strength is reduced. But this method, at the same time, reduces the safety of the operation of power lines.
Another area of research is wire selection. After all, heat loss and other indicators depend on their properties. In addition, during the operation of heating devices, a large amount of energy is released. Therefore, spirals are made from materials specially designed for this purpose, capable of withstanding high loads.
Household fuses
To improve protection and secure electrical circuits, special fuses are used. The main part is a wire made of low-melting metal. It runs in a porcelain cork, has a screw thread and a contact in the center. The cork is inserted into a cartridge located in a porcelain box.
Lead wire is part of a common chain. If the thermal effect of the electric current increases sharply, the cross section of the conductor will not withstand, and it will begin to melt. As a result of this, the network will open, and there will be no current overloads.
Electric arc
The electric arc is a fairly efficient converter of electrical energy. It is used when welding metal structures, and also serves as a powerful light source.
The device is based on the following. Take two carbon rods, connect the wires and attach them in insulating holders. After that, the rods are connected to a current source, which gives a small voltage, but is designed for a large current. Connect the rheostat. It is forbidden to turn on coals in the city network, as this can cause a fire. If you touch one coal to another, you can see how hot they are. It is better not to look at this flame, because it is harmful to the eyes. An electric arc is used in metal melting furnaces, as well as in such powerful lighting devices as searchlights, movie projectors, and so on.
