The reason for the heating of the conductor lies in the fact that the energy of the electrons moving in it (in other words, the energy of the current) is converted into a warm type of energy, or Q, in the sequential collision of particles with the ions of the molecular lattice of a metal element, and the concept of “thermal power” is formed.
The work of the current is measured using the international SI system of units, applying joules (J) to it, the current power is defined as “watts” (W). Departing from the system in practice, they can also use off-system units that measure the current. Among them, watt-hour (W × h), kilowatt-hour (abbreviated kW × h). For example, 1 W × h means current with a specific power of 1 watt and a duration of one hour.
If electrons move along a fixed conductor of metal, in this case all the useful work of the generated current is distributed to heat the metal structure, and, based on the provisions of the energy conservation law, this can be described by the formula Q = A = IUt = I 2 Rt = (U 2 / R) * t. Such relations accurately express the well-known Joule-Lenz law. Historically, it was first experimentally determined by the scientist D. Joule in the middle of the 19th century, and at the same time, by another scientist E. Lentz independently. The thermal power has found practical application in technical performance since the invention in 1873 by the Russian engineer A. Ladygin of an ordinary incandescent lamp.
Thermal current power is used in a number of electrical appliances and industrial installations, namely, in thermal measuring instruments, heating type electric stoves, electric welding and inventory equipment, household appliances with an electric heating effect are very common - boilers, soldering irons, kettles, irons.
The thermal effect also finds itself in the food industry. With a high proportion of use, the possibility of electrical contact heating is used, which guarantees thermal power. It is caused by the fact that the current and its thermal power, affecting a food product that has a certain degree of resistance, causes uniform heating in it. You can give an example of how sausages are made: through a special dispenser, minced meat comes in metal forms, the walls of which simultaneously serve as electrodes. This ensures uniform heating throughout the entire area and volume of the product, maintains the set temperature, maintains the optimal biological value of the food product, along with these factors, the duration of the technological work and energy consumption remain the smallest.
The specific thermal power of the electric current (ω), in other words, the amount of heat that is released in a unit volume for a certain unit of time, is calculated as follows. The elementary cylindrical volume of the conductor (dV), with the cross-sectional conductor cross section dS, length dl parallel to the direction of the current, and resistance are the equations R = p (dl / dS), dV = dSdl.
According to the definitions of the Joule-Lenz law, in the allotted time (dt) in the volume taken by us, a heat level equal to dQ = I 2 Rdt = p (dl / dS) (jdS) 2 dt = pj 2 dVdt will be released. In this case, ω = (dQ) / (dVdt) = pj 2 and, applying Ohm's law here to establish the current density j = γE and the relation p = 1 / γ, we immediately obtain the expression ω = jE = γE 2. It is in differential form gives the concept of the Joule-Lenz law.