Kirchhoff's laws, explain in simple terms

With the first and second laws of Kirchhoff's and Ohm's law scheme parameters can be found any difficulty. Therefore, knowledge and understanding of the most important of these three laws is strictly necessary for all those involved in electronics. In this article I will try to explain as simply and simple diagrams to show how the laws of Kirchhoff work. So let's start.

The first law of Kirchhoff

Thus, the first Kirchhoff's law tells us that the sum of the currents at any node absolutely any electrical circuit is zero. Or so he says that the algebraic sum of the currents flowing equal to the algebraic sum of the currents flowing from the node.

Node in the network is called a circuit portion, connecting three or more conductor. The current node belongs to is denoted by an arrow having a direction to the node, and flowing - arrow having a direction from node

And now, on the basis of the first Kirchhoff's law we can write the following equation:

The same formula can be written as follows:

In this case, the positive and negative signs of the currents are assigned to probation and if you change them exactly the opposite, there is nothing fundamentally will not change.

In order to clearly see the work of the First Kirchhoff's law, let's put it the simplest scheme.

As a power source, you can choose absolutely any element from the penlight batteries and finishing power supply with adjustable.

Note. Not necessary to use resistors with a nominal value of which is specified in the diagram. You can choose absolutely any, what do you have in stock.

Thus, according to the 1 Kirchhoff's law we must be true, the following equation:

Either true:

For practical measurements we need to place on the circuit where the Set an ammeter connected, for example, a multimeter.

As we can see on the meter readings of the law works.

Kirchhoff's second law

With an understanding of the second law of many amateur radio operators at the beginning of the path there are difficulties. But if it is explained in a simple way, then more than now prove.

Thus, the definition of the second Kirchhoff's law is:

In any closed loop circuit EMF algebraic sum equal to the algebraic sum of the voltages on all of passive circuit elements.

Agree, sounds not very clear, but if it is easier to say:

Amount in a closed circuit EMF is the sum of the voltage drops and the formula expressing the law will be of the form

Or

To understand, let's analyze the most simple shemku one passive element (resistor) and a power source in the form of finger-type batteries.

Since we have a resistor, the voltage drop across its terminals is equal to the electromotive force the battery (batteries), ie 1.5 V = 1.5 V.

If multiple circuit complicate and add to another resistor with the same resistance, in this case, the voltage of 1.5 volts is halved resistors and is equal to 0.75 V.

As the voltage division will occur if we are in a chain including the third resistor with the same resistance.

The formula will find the following form:

Let's understand this scheme and collect the measurement.

As you can see, the second law of Kirchhoff slight difference in the readings of the meter will charge to the instrument error (china as in any way).

Besides a single power supply circuit may be several such as, for example, in this scheme,

In this case, we have two sources of power are connected in series in opposition, in this embodiment, the resistors will our difference is applied emf, i.e. acquire the formula as follows:

Kirchhoff's second law operates in chains no matter how many sources of electromotive force and load is in the circuit. Just as there is no fundamental difference where they are located.

As the first and second laws of Kirchhoff equally applicable to both DC and AC.

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