**Basic Electrical Laws:**

In this page, we had given various fundamental electrical laws and theorems. When we are keep on reading advanced power electronics topics, we will forget the basic electrical laws. This page will serve as a ready reference to recall the fundamental electrical theorems. If you have any suggestions about this page please share with us which will be useful to improve this page.

Here the following laws/theorems are covered:

Coulomb's Law of electrostatics

Lenz's Law

Kirchhoff's Laws

Faraday’s law

Superposition Theorem

Thevenin’s theorem

Norton’s theorem

The maximum power transfer theorem

Ohm's Law

**Coulomb's Law of electrostatics:**

First Law:

Like charges repel each other while unlike charges attract each other.

Second Law:

It states that the force between two charged bodies is directly proportional to the product of the charges and is inversely proportional to the square of the distance between their centres.

**Lenz's Law:**

It states that the polarity of an induced emf is always such that it opposes the change which produced it.

**Kirchhoff's Laws:**

First Law (Point or Current Law):

The sum of the currents entering a junction is equal to the sum of the currents leaving the junction.

Second law (Mesh or Voltage Law):

It states that the algebraic sum of the potential drops in a closed network (mesh) is zero.

**Faraday’s law: **

It states that the voltage induced in a circuit by a changing magnetic field is equal to the rate at which the flux linking the circuit is changing.

**Superposition Theorem:**

In any network containing more than one source of emf the current in any branch is the algebraic sum of a number of individual fictitious currents (the number being equal to the number of sources of emf) each of which is due to the separate action of each source of emf taken in order, when the remaining sources of emf are replaced by conductors, the resistances of which are equal to the internal resistances of the respective sources.

**Thevenin’s theorem:**

The current in any branch of a network is that which would result if an e.m.f. equal to the voltage across a break made in the branch, were introduced into the branch, all other e.m.f.’s being removed and represented by the internal resistances of the sources.

**Norton’s theorem:**

The current that flows in any branch of a network is the same as that which would flow in the branch if it were connected across a source of electrical energy, the short-circuit current of which is equal to the current that would flow in a short-circuit across the branch, and the internal resistance of which is equal to the resistance which appears across the open-circuited branch terminals.

**The maximum power transfer theorem:**

The power transferred from a supply source to a load is at its maximum when the resistance of the load is equal to the internal resistance of the source.

**Ohm's Law:**

The ratio of potential difference(V) between any two points of a conductor to the current(I) flowing between them is constant, provided the temperature of the conductor does not change.

ie, V/I = Constant = R

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