Moving in any conductor, an electric current transfers some energy to it, which causes the conductor to heat 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 particles of the conductor. Then its internal energy 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 passes 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=UIt.
The amount of heat can be denoted by Q. Then Q=A or Q=UIt. Knowing that U=IR,it turns out Q=I2Rt, which was formulated in the Joule-Lenz law.
The law of the thermal action of the current - the Joule-Lenz law
The conductor where the electric current flows has been studied by many scientists. However, the most notable results were achieved by James Joule from England and Emil Khristianovich Lenz from Russia. Both scientists worked separately and the conclusions based on the results of the experiments were made independently of one another.
They derived a law that allows you to estimate the heat received as a result of the action of current on a conductor. They called it the Joule-Lenz law.
Let's consider in practice the thermal effect of the current. Take the following examples:
- A regular light bulb.
- Heaters.
- Fuse in the apartment.
- Electric arc.
Incandescent bulb
The thermal effect of current and the discovery of the law contributed to the development of electrical engineering and increased opportunities for the use of electricity. How the research results are applied can be seen in the example of an ordinary 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 only due toa small part of the energy, it begins to glow. The main part just heats up.
To better understand this, an efficiency factor 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 appliances
Usually, in the design of all devices for heating there is a metal spiral, the function of which is heating. If water is heated, then the coil is installed in isolation, and in such devices a balance is maintained between energy from the network and heat exchange.
Scientists are constantly challenged to reduce energy losses and find 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 power transmission is used, thereby reducing the current strength. 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, the spirals are made from materials specially designed for this purpose, capable of withstanding high loads, materials.
Apartment fuses
Special fuses are used to improve the protection and safety of electrical circuits. 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 the cartridge located in the porcelain box.
The 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 current overloads will not happen.
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. The electric arc is used in metal smelting furnaces, as well as in such powerful lighting devices as spotlights, movie projectors, etc.
