The reason for heating the conductor lies in the fact that the energy of the electrons moving in it (in other words, the energy of the current) in the sequential collision of particles with ions of the molecular lattice of a metal element is converted into a warm type of energy, or Q, so the concept of "thermal power" is formed "".
The work of the current is measured using the international system of units SI, applying joules (J) to it, the power of the current is defined as "watt" (W). Deviating from the system in practice, they can also use off-system units that measure the work of the current. Among them are watt-hour (W × h), kilowatt-hour (abbreviated kW × h). For example, 1 Wh indicates the work of a current with a specific power of 1 watt and a time duration of one hour.
If electrons move along a fixed metal conductor, 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 law of conservation of energy, this can be described by the formula Q=A=IUt=I 2Rt=(U2/R)t. Such ratios accurately express the well-known Joule-Lenz law. Historically, it was first determined empirically by a scientistD. Joule in the middle of the 19th century, and at the same time independently of him by another scientist - E. Lenz. Thermal power has found practical application in technical design since the invention in 1873 by Russian engineer A. Ladygin of an ordinary incandescent lamp.
The thermal power of the current 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 on the electric heating effect are very common - boilers, soldering irons, kettles, irons.
Finds itself a thermal effect in the food industry. With a high share of use, the possibility of electrocontact heating is used, which guarantees thermal power. It is due to the fact that the current and its thermal power, influencing the food product, which has a certain degree of resistance, causes uniform heating in it. We can give an example of how sausages are produced: through a special dispenser, minced meat enters metal molds, the walls of which simultaneously serve as electrodes. Here, constant uniformity of heating is ensured over the entire area and volume of the product, the set temperature is maintained, the optimal biological value of the food product is maintained, together with these factors, the duration of technological work and energy consumption remain the smallest.
Specific heatthe power of the electric current (ω), in other words, the amount of heat that is released per unit volume for a certain unit of time, is calculated as follows. An elementary cylindrical volume of a conductor (dV), with a conductor cross section dS, a length dl parallel to the direction of current, and a resistance form the equations R=p(dl/dS), dV=dSdl.
According to the definitions of the Joule-Lenz law, for the allotted time (dt) in the volume taken by us, a heat level equal to dQ=I2Rdt=p(dl/dS)(jdS)2dt=pj2dVdt. In this case, ω=(dQ)/(dVdt)=pj2 and, applying here Ohm's law to establish the current density j=γE and the ratio p=1/γ, we immediately obtain the expression ω=jE=γE2. It gives the concept of the Joule-Lenz law in differential form.
