The calculations of electric AC and DC besides the famous formula Ohm's law also applies Kirchhoff.The man, whose work is linked to electrical engineering, should not even middle of the night without hesitation to give definitions for each of the two laws.Often it is necessary not only to perform calculations as for the understanding of the processes.
Back in 1845 the German physicist Gustav Kirchhoff based on the works of Maxwell (conservation of charge and properties of electrostatic fields) formulated two rules for specifying the relationship between current and voltage in a closed circuit.This made it possible to solve almost any application problem related to electricity.Kirchhoff's law used to calculate a linear electric circuit, makes it possible to obtain a classical system of linear equations that take into account the voltage and currents that become known after the task.
The formulation involves the use of terms electrical "circuit node and branch."Branch - a two-way any portion of the circuit, an arbitrary length of it.The circuit - a system obsessed branches, that is, starting a mental movement of any point on any branch, in the end still get into the place where the movement began.More clear branches called "roll over", although this is not entirely correct.Host - this is the point at which two or more branches.
1 Kirchhoff's law is very simple.It is based on the fundamental law of conservation of charge.The first Kirchhoff's law states: the sum of currents (algebraic), runs down the branches to a single node is equal to zero.I.e., I1 + I2 + I3 = 0.For the calculation it is assumed that the value of current flowing into the node has a "+" sign, and the resulting "-".Therefore, the expanded formula takes the form I1 + I2 - I3 = 0. In other words, the amount of current flowing into a node is equal to the outflow.This Kirchhoff's law is very important for an understanding of the principles of electrical equipment.For example, he explains why when connecting the electric motor windings on a "star" or "triangle" there is no interphase short circuit.
2 Kirchhoff's law is generally used for the calculation of the closed loop with a number of branches.It is directly correlated with the third law of Maxwell (constant magnetic field).The rule states that the algebraic sum of the voltage drop across each of the branches of the circuit is equal to the sum of the values for all branches of the EMF calculated contour.Clearly, in the absence of a closed circuit of electrical power sources (EMF), the resulting voltage drop will be zero.In more simple terms, the energy source is only converted to consumers, and aims at returning to its original value.Using this law has a number of features, as is the case with the first.
equating circuit, it is assumed that the numerical value of EMF is positive if initially accepted the contour direction (typically clockwise) coincides with its direction, and negative if the opposite direction.The same applies to resistors: If the direction of the current is the same as the selected bypass, the voltage drop across it is attributed to "+" sign.For example, E1 - E2 + E3 = I1R1 - I2R2 + I3R3 + I4R4 ...
a result of circumvention of all branches belonging to the circuit components of the system of linear equations, solving that, it is possible to learn all the branch currents (and units).Solved the relations obtained using mesh analysis.
is difficult to overestimate the importance of Kirchhoff's laws for electrical engineering.Ease of writing formulas and their solution by the methods of classical algebra were the reason for the wide use.
