when do we use the thevenin's theorem and norton's theorem?

Question

can i ask

Answer 1

Thevenin's thm gives you the equivalent representation of a network in terms of an ideal VOLTAGE source with a SERIES impedance and Norton's thm gives you the equivalent representation of a network in terms of an ideal CURRENT source with a PARALLEL impedance. These equivalent circuits are "duals" of each other and can be used interchangeably. Where to use which one is a fairly general/vague question and you will have to determine if you need the network equivalent with a current source [could be required in transistor circuits based upon "current mirrors" or while designing for current sensing/current limiting applications, working with constant current loads (heavily inductive loads)etc.] or voltage source; as an example, the standard equivalent circuit of a battery with a small series resistance is technically a Thevenin's equivalent circuit which models the complicated chemical phenomenon into an ideal voltage source and series resistance.
The current source based model of a well known electrical source is the model of a silicon solar cell...but beware! it is not a Norton equivalent and includes diode (active element). The point is to illustrate that both sources (V and I) find use in modeling.
So remember:
current source, parallel impedance - Norton
voltage source, series impedance - Thevenin
NOTE: These models are applicable to dc and single frequency ac.
*This NOTE is not correct: Look at Doug's explanation* Thanks Doug!

Answer 2

2

Answer 3

DAMN!!
It sounds as if Saurabh T has actually paid attention in class and learned this stuff. Good for him. Keep it up.

Just for him: In the most general case you can actually replace the Thevenin (or Norton) resistance with a generalized impedance and use that the same way you would the simpler 'resistive' model. It's kinda useful for RF stuff because it makes it easier to match impedances for maximum power transfer.

Doug