These concepts are dealt with by Norton's theorem and Thévenin's theorems.

Norton's theorem states that any two-terminal network can be reduced to an ideal current generator and a parallel impedance.

Application of Thévenin's theorem and Norton's theorem gives the quantities associated with the equivalence.

The theorem is well-known under the name Norton's theorem or Mayer-Norton theorem.

Norton's theorem: any two-terminal collection of voltage sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor.

This process is known as a source transformation, and is an application of Thévenin's theorem and Norton's theorem.

Notice that here the input representation satisfies Thévenin's theorem while the output representation satisfies Norton's theorem.

In general, the concept of source transformation is an application of Thévenin's theorem to a current source, or Norton's theorem to a voltage source.

Thévenin's theorem and its dual, Norton's theorem, are widely used for circuit analysis simplification and to study circuit's initial-condition and steady-state response.

The passive circuit equivalent of "Norton's theorem" in queuing theory is called the Chandy Herzog Woo theorem.

Known in Europe as the Mayer-Norton theorem, Norton's theorem holds, to illustrate in DC circuit theory terms, that (see image):

For instance, one might transform a voltage generator into a current generator using Norton's theorem in order to be able to later combine the internal resistance of the generator with a parallel impedance load.

Depending on perspective, this impedance can be modeled as being in series with an ideal voltage source, or in parallel with an ideal current source (see: Thévenin's theorem, Norton's theorem, Series and parallel circuits).

Just as impedance extends Ohm's law to cover AC circuits, other results from DC circuit analysis such as voltage division, current division, Thévenin's theorem, and Norton's theorem can also be extended to AC circuits by replacing resistance with impedance.