Revision of Basic Electrical Engineering Laws and Theorems

Basic Electrical Engineering Laws and Theorems

  1. Ohm’s law

  2. Kirchhoff’s current law

  3. Kirchhoff’s voltage law

  4. Superposition principle

  5. Thevenin theorem

  6. Norton theorem

  7. Maximum power transfer theorem

  8. Substitution theorem

  9. Millman theorem


Ohm’s law

Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship

V = IR

Ohm’s Law

Kirchhoff’s current law

The total current entering a junction or a node is equal to the charge leaving the node as no charge is lost.

Put differently, the algebraic sum of every current entering and leaving the node has to be null. This property of Kirchhoff law is commonly called as Conservation of charge

∑ Current In = ∑ Current out

Kirchhoff’s voltage law

The voltage around a loop equals to the sum of every voltage drop in the same loop for any closed network and also equals to zero.

Put differently, the algebraic sum of every voltage in the loop has to be equal to zero and this property of Kirchhoff’s law is called as conservation of energy.

∑ Voltage rise = ∑ Voltage drop

Superposition principle

Many electrical circuits contain a single source powering different resistors. Sometimes a circuit contain multiple current and voltage sources. A superposition principle is applied to all circuits having multiple sources.

The voltage or current appearing across any component is equal to the sum of individual voltage or current of all independent sources.

Thevenin theorem

Thevenin’s Theorem states that “Any linear circuit containing several voltages and resistances can be replaced by just one single voltage in series with a single resistance connected across the load“.

Norton theorem

Norton’s Theorem states that it is possible to simplify any linear circuit, no matter how complex, to an equivalent circuit with just a single current source and parallel resistance connected to a load

Maximum power transfer theorem

In electrical engineering, the maximum power transfer theorem states that, to obtain maximum external power from a source with a finite internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals.

Substitution theorem

Substitution Theorem states that the voltage across any branch or the current through that branch of a network being known, the branch can be replaced by the combination of various elements that will make the same voltage and current through that branch. In other words, the Substitution Theorem says that for branch equivalence, the terminal voltage and current must be the same.

Millman’s Theorem

In electrical engineering, Millman’s theorem (or the parallel generator theorem) is a method to simplify the solution of a circuit. Specifically, Millman’s theorem is used to compute the voltage at the ends of a circuit made up of only branches in parallel. It is named after Jacob Millman, who proved the theorem.


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