Chapter 12


The characteristics of dipoles

FondamentalConventions generator and receptor

Conventions generator and receptor

If two dipoles are interconnected, conventions are necessarily receptor for one and generator for the other.

The arbitrary choice of conventions does not say much for the type of real operation (generator or receiver) of the dipole.

FondamentalCharacteristic of a dipole

Called dipole characteristic one of the following curves, giving either as a function of or as a function of .

Characteristic of a dipole

FondamentalCharacteristic ohmic conductors, Ohm's law

Ohm's Law (see also "Local Ohm's law") :

is the conductor resistance (expressed in ohm, )

Or :

Where is the conductance of the conductor (expressed in Siemens, ).

Ohm's Law

Associations of ohmic conductors :

  • In series :

    The resistors are added :

  • In parallel (in derivation) :

    Conductances are added :

    Is :

JAVA animation (of JJ.Rousseau, University of Le Mans) on the color code of resistance :

Click HERE

FondamentalCharacteristics of generator (linear active dipole)

The characteristic of a generator (generator convention) is given in the following figure.

It is a linear active dipole, whose characteristic can be modeled as :

With :

  • : open circuit voltage ( ), measured with a voltmeter.

  • : Short circuit current ( ), measured with an ammeter.

Characteristics of generator

We denote :

So :

The linear active dipole is thus equivalent to the following two elements in series :

  • An ideal emf generator voltage denoted (equal to open circuit voltage at the terminals of the dipole).

  • Ohmic conductor resistance (internal resistance of the active dipole).

This modeling of the active dipole is called "Thevenin's modeling"

Thevenin's model

Norton's modeling :

The linear active dipole is equivalent to the following two elements placed in parallel :

  • An ideal current generator of electromotive current (equal to the short-circuit current of the active dipole),

    in parallel with :

  • ohmic conductor resistance (internal resistance of the active dipole).

This modeling of the active dipole is called "Norton's modeling".

Norton's model

One passes from the representation of the Thevenin to Norton using the following relationships :

FondamentalFundamental associations linear active dipole

Series (choice of Thevenin model) :

The emf are added (algebraically) and internal resistances are added :

Series (choice of Thevenin model) :

In parallel (choice of Norton model) :

Electric currents are added (algebraically) and conductance are added :

In parallel (choice of Norton Model):
Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL)
Additional exercises