Chapter 2
Theorems of DC
These are useful at the time of solving certain circuits where the associations of components have some complexity. But the important ones are: Laws of Kirchoff and theorems of Thévenin and Norton.
They are two and one knows with the name law the nodes or knots and law of you respectively enmesh or first law of Kirchoff and second law of Kirchoff.
Law of the nodes: The sum of the current intensities that arrive at a node is equal to the sum of the current intensities that leave him.
Law of you enmesh: In a closed circuit (it enmeshes) the algebraic sum of the electromotrices forces in enmeshes is equal to the sum of products of each resistance of the same by the current that circulates around her.
When we have a unknown circuit, in which we have accessible two tips of the same, we can apply the theorem of Thévenin to obtain an equivalent circuit of this one.
The theorem says the following thing: All circuit that has two accessible terminals (To and B) could in series be represented by an equivalent made up of a source of equivalent tension VTH connected with an equivalent resistance RTH. In order to obtain the values of VTH and RTH it is made:
RTH will be the resistance that presents/displays the circuit enters the terminals and B when all the sources of tension are cortocircuiten in the original circuitry and the generators are left open circuit.
VTH will be the present tension enters the tips and B with these abiertos (without connecting).
In the figure we applied the theorem of Thévenin to the circuit to and obtained its Thévenin equivalent that is circuit d.
This theorem expresses that all circuitry that presents/displays two accessible terminals (To and B) could be replaced by an equivalent ideal circuit that is formed by an equivalent resistance Rn in parallel with an ideal source of current In.
The value of Rn is obtained from identical form that the equivalent resistance Thévenin RTH and In it is the current that circulates around branch A-B.
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