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Laws describing the operation of an electrical circuit

Lecture



Ohm's law - current strength is directly proportional to the applied voltage and inversely proportional to the resistance of the conductor.

  Laws describing the operation of an electrical circuit

Generalized Ohm's law for the active branch:

  Laws describing the operation of an electrical circuit

Rule: EMF and voltage are taken with a “+” sign, if their directions coincide with the direction of the current, and with a “-” sign, if not.

Kirchhoff's laws
1st law: the algebraic sum of the currents of the branches converging in one node is zero. Rule: the current flowing into the node is taken with a "+" and flowing with a "-".
Σ Ii = 0, for example:

I1 + I2 - I3 = 0

  Laws describing the operation of an electrical circuit

2nd law: the algebraic sum of voltages on the resistive elements of a closed active circuit macn (Fig. 1) is equal to the algebraic sum of the emf included in this circuit.

ΣRi • Ii = ΣEi

Example: Let's make an equation according to the 2nd Kirchhoff's law for 1 circuit and for 2 circuit, Fig. 1:

  Laws describing the operation of an electrical circuit   Laws describing the operation of an electrical circuit

the algebraic sum of the voltages of all sections of the closed passive loop abcd (Fig. 1) is 0.

ΣUi = 0

The rule is: if the emf and current have the same direction as the circuit bypass direction, then they are taken from “+”, if not, then from “-”.

Joule-Lenz law
Power source e. energy is defined as the product of current and voltage:

Pist = U • J or Rist = E • I

The power of the receiver is defined as the product of the square of the current and the resistance of the branch:

Rpr = I² • R

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Electrical Engineering, Circuit design

Terms: Electrical Engineering, Circuit design