Moving in any conductor, an electric current transfers some kind of energy to it, because of which the conductor heats up. Energy transfer is carried out at the molecular level: as a result of the interaction of current electrons with the ions or atoms of the conductor, some of the energy remains with 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 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 the internal conductor energy. In this case, 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 the 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, we get Q = I 2 * R * t, which was formulated in the Joule-Lenz law.
The law of thermal action of current - the Joule-Lenz law
The conductor, where electric current flows , was studied by many scientists. However, the most noticeable results were achieved by James Joule from England and Emilia Khristianovich Lenz from Russia. Both scientists worked separately and made conclusions from the results of experiments independently of one another.
They deduced a law that allows one to evaluate the heat produced by the action of current on a conductor. It was called the Joule-Lenz law.
Let us consider in practice the thermal effect of current. Examples are the following:
- An ordinary light bulb.
- Heating appliances.
- Fuse in the apartment.
- Electric arc.
Light bulb
The thermal effect of the 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 considered with an ordinary incandescent bulb as an example.
It is arranged in such a way that a thread made of tungsten wire is drawn inside. This metal is refractory with high resistivity. When passing through a 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 a light bulb is a large energy loss, since only due to an insignificant part of the energy does it begin to glow. The main part just heats up.
To better understand this, a performance factor is introduced that demonstrates the efficiency of work and conversion to electricity. Efficiency and thermal 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 devices for heating there is a metal spiral, the function of which includes heating. If water is heated, then the spiral is installed in isolation, and such devices provide for the balance between the energy from the network and heat exchange.
Scientists are constantly given 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 energy transfer, thereby reducing the current strength. But this method, at the same time, reduces the safety of the functioning of power lines.
Another research area is the selection of wires. After all, heat losses and other indicators depend on their properties. In addition, during the operation of heating devices there is a large release of energy. Therefore, spirals are made from materials specially designed for these purposes, capable of withstanding high loads.
Apartment fuses
To improve protection and secure electrical circuits, special fuses are used. The role of the main part is a wire made of fusible metal. It passes in a cork made of porcelain, has a screw thread and a contact in the center. The cork is inserted into the cartridge located in the porcelain box.
Lead wire is part of a common circuit. 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 effective converter of electrical energy. It is used in welding metal structures, and also serves as a powerful light source.
The basis of the device includes the following. Take two coal 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 strength. Connect the rheostat. It is forbidden to include coal in the city network, as this can cause a fire. If you touch one coal with another, you can see how much they will heat up. It is better not to look at this flame, because it is harmful to vision. An electric arc is used in furnaces for melting metal, as well as in such powerful lighting devices as projectors, film projectors, and more.