About Kirchhoff s second rule

The meaning of Kirchhoff's law is that in a closed loop, each element causes the electric potential to rise (fall), but the sum of the electric potential rises and falls along a circle is 0, that is, starting from a point, the electric potential changes along this circuit, but when it returns to this point, the electric potential should be equal to the value before the change, that is, the change is zero. If this is not the case, different potentials will be created at the same point, so that the charge will continue to accelerate and gain energy.

Only the vortex electric field has such a property, but the vortex electric field must have an external energy input, while the closed loop does not, because the energy is conserved, so it must satisfy Kirchhoff's law.

I don't know much about this, but I found relevant information on Wikipedia, I hope it will be helpful to you.

You can go directly to Wikipedia for the term "Kirchhoff's circuit law".

Kirchhoff's voltage law (Kirchhoff'S voltage law (KVL) is also known as Kirchhoff's second law'S Second Law), Kirchhoff's Cycle Law (Kirchhoff's loop rule) and Kirchhoff's second rule's second rule）。This is the result of conservation of energy.

The principle of conservation of energy states:

The direct sum of the potential differences around a circuit must be zero. ”

Otherwise, it is possible to build a perpetual motion machine that allows the current to circulate in the circuit. Considering that the electric potential is defined as the line integral of the electric field, then Kirchhoff's voltage law can be expressed as:

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This equation indicates that the integral of the electric field lines around the return point c is zero.

This is the application of Faraday's law of electromagnetic induction (faraday's law of induction) is a simplified version of a special case in which no fluctuating magnetic field is attached to the closed loop. If there is a magnetic field in a wave, the electric field is not conserved, then there is no way to define a pure scalar potential—the integral of the electric field line around the return point is not zero. This is because the magnetic field transfers energy to the electric current, which in turn transfers energy to the magnetic field.

In order to modify Kirchhoff's voltage law so that it can be applied to circuits with inductors, an electric potential drop or electromotive force is applied to each inductor in the circuit, which is exactly equal to the line integral of the electric field (based on Faraday's law of electromagnetic induction, this line integral is not equal to zero).

The direction of the current is based on the direction marked in the circuit, and the real current is positive if it is the same as the marked direction, and the opposite is negative.

The same or opposite method of judging the true direction is to look at the current direction in the resistor, and the end that encounters the high resistance voltage first is positive, and the end that encounters the low resistance voltage first is negative.

In short, the direction of the current in the circuit is artificially defined, and it is a different concept from the direction of the real current, so the problem of negative current occurs. Negative current means that the true direction of the current is the opposite of the artificially defined direction.

There is only one rule for the definition of current direction: there can only be one current direction on the same branch. The rest is at will. For example, in the above circuit, it is completely possible to define the direction of i3 to face upward. In that case, the final result of the calculation is a negative value of i3.

For the nodes of the three branches, the currents on the three branches must be different, because the algebraic sum of the currents flowing into the nodes is 0, so it must be that the current of one of the branches is the sum of the other two currents. For example, i3, i1, i2. If the three currents are all the same, only if i1, i2, and i3 are all 0, the equation cannot be true.

Kirchhoff's law is written as follows: i1 i2 i3 0. (In this case, the current flowing into the node is defined as positive, and i3 is outflowing, so it is negative).

If the direction of i3 is drawn upward, it is i1 i2 i3 0. (At this point, the direction of i3 is opposite to the true direction, so the result i3 must be negative).

If the current of the same branch is equal, the same circuit is not necessarily equal. i1i2i3 is an electric current through a resistor. The bull law A is positive and negative in the same direction as V0. The current goes around the direction of the regular voltage drop is positive, and the voltage rise is negative.