Ohm's law is one of the basic tenets of physics. The general formula, valid both for the complete circuit and for its section, indicates that the current strength is equal to the quotient obtained by dividing the value expressing the voltage in volts by the value expressing the current in amperes. This dependence shows that with a decrease in resistance, the current strength increases. The question arises: is it possible to obtain the maximum current strength by reducing the resistance to zero? Practice shows that this is impossible. Ohm's law for a complete circuit suggests that the voltage should be divided by the total, total resistance, calculated as the sum of the external resistance and internal resistance, depending on the current source. It is not possible to reduce the internal resistance of the system to zero. Otherwise, the probability of battery explosion is very high.
What is the internal and external resistance that Ohm's law speaks of for the complete chain? If, for example, a bulb is connected to the circuit, then the resistance of this bulb will be external. Internal resistance always comes from the battery, that is, it is formed inside the system itself. If a galvanic cell is used instead of a battery , then Ohm's law for the entire circuit takes into account the resistance of the electrolyte solution and electrodes. If the external resistance is several times less than the internal resistance and the circuit is closed, then a short circuit current flows through it. This is the maximum amount of current that can pass through this circuit. Current sources in automobiles show values of short circuit current that are critically life-threatening. For safety reasons, they are connected to external battery devices with sufficient resistance to prevent tragedy.
When connected in series, the total internal resistance of the circuit is calculated by adding the resistances of each current source. With a parallel connection, the voltage at each of the branch sections has the same value, and the current strength in the unbranched circuit is calculated by adding up the values that show the ammeters on each of the sections connected in parallel. A current source located in a circuit section does not exert any influence on the section connected in parallel with it.
Where do Ohm's laws apply for the complete chain? Mostly they are used to calculate the current strength in linear DC electric circuits . In order to perform the calculations correctly, it is necessary to remember the postulates of Kihgof. Firstly, the algebraic sum of the current forces located in a node is equal to zero. Secondly, the product of the algebraic sum of the currents in a closed circuit of a branched chain and the resistance of sections of a given circuit is always equal to the algebraic sum of the voltage detected in the circuit.
Under what conditions, how and when was Ohm's law discovered for the complete chain? Swiss researcher Georg Simon Om came to the formula now known to the whole world empirically. He studied the magnetic action of current and set up experiments with various generators, used conductors from various metals and alloys in his experiments. Ohm became the first physicist to note the effect on the resistance of conductors of their temperature. Ohm's law for the full chain was not immediately recognized by the scientific community. The first scientists to appreciate this law were the Russian researchers Jacobi and Lenz. The American J. Henry later compared the formula expressing Ohm's law for a complete chain with lightning in the middle of an empty gloomy room, and German professor E. Lommel called the discovery "a bright torch in the field of electricity."