Question

Can someone explains to me the Thevenins theorem?

Answer 1

This theorem states that a circuit of voltage sources and resistors can be converted into a Thévenin equivalent, which is a simplification technique used in circuit analysis
now it could be seen from the diagram that the all voltage sources ,current sources and resistors are converted to single voltage source with a single series resistor..it is just a method to simplify the circuit diagram as one uses kirchoff's law to find voltage across two points by kvl or current with in a branch by kcl one can do the same with this method...
firstly to understand thevnin's theorem you should be understanding about voltage and current sources..
n electric circuit theory, an ideal voltage source or constant voltage (CV) source is a circuit element where the voltage across it is independent of the current through it. A voltage source is the dual of a current source. In analysis, a voltage source supplies a constant DC or AC potential between its terminals for any current flow through it. Real-world sources of electrical energy, such as batteries, generators, or power systems, can be modeled for analysis purposes as a combination of an ideal voltage source and additional combinations of impedance elements....
and now if we could also talk about independent and dependent voltage source..
. If the voltage across an ideal voltage source can be specified independently of any other variable in a circuit, it is called an independent voltage source. Conversely, if the voltage across an ideal voltage source is determined by some other voltage or current in a circuit, it is called a dependent or controlled voltage source
Calculating the Thévenin equivalent

To calculate the equivalent circuit, the resistance and voltage are needed, so two equations are required. These two equations are usually obtained by using the following steps, but any conditions placed on the terminals of the circuit should also work:
Calculate the output voltage, VAB, when in open circuit condition (no load resistor—meaning infinite resistance). This is VTh.
Calculate the output current, IAB, when the output terminals are short circuited (load resistance is 0). RTh equals VTh divided by this IAB.
The equivalent circuit is a voltage source with voltage VTh in series with a resistance RTh.
Step 2 could also be thought of as:
2a. Replace voltage sources with short circuits, and current sources with open circuits.
2b. Calculate the resistance between terminals A and B. This is RTh.
The Thévenin-equivalent voltage is the voltage at the output terminals of the original circuit. When calculating a Thévenin-equivalent voltage, the voltage divider principle is often useful, by declaring one terminal to be Vout and the other terminal to be at the ground point.
The Thévenin-equivalent resistance is the resistance measured across points A and B "looking back" into the circuit. It is important to first replace all voltage- and current-sources with their internal resistances. For an ideal voltage source, this means replace the voltage source with a short circuit. For an ideal current source, this means replace the current source with an open circuit. Resistance can then be calculated across the terminals using the formulae for series and parallel circuits. This method is valid only for circuits with independent sources. If there are dependent sources in the circuit, another method must be used such as connecting a test source across A and B and calculating the voltage across or current through the test source.
one should keep in mind when replacing a circuit with other circuit the voltage between the elements or voltage drop should be independent..of the the modification we do that's the point for equivalent circuit and we are here describing the ways to get thevinin's equivalent circuit by thevinin's theorem ...

Answer 2

hope it helps!! and if you want to know about equivalent circuits http://en.wikipedia.org/wiki/Equivalent_circuit
because both norton's and thevin's theorem focus on drawing an equivalent circuit except thevinin's focus on cicuit with independent voltage source whilt norton's on current source...!!

Answer 3

i go it thanks. I just have to read it again to get a better understanding.

Answer 4

Tell me @shivaniits do you understand superposition theorem?

Answer 5

good to know it helped!!
superpostion theorm amm.. i don't know much but i have a brief idea!! may be that work
The superposition theorem for electrical circuits states that for a linear system the response (Voltage or Current) in any branch of a bilateral linear circuit having more than one independent source equals the algebraic sum of the responses caused by each independent source acting alone, while all other independent sources are replaced by their internal impedances.
To ascertain the contribution of each individual source, all of the other sources first must be "turned off" (set to zero) by:
Replacing all other independent voltage sources with a short circuit (thereby eliminating difference of potential. i.e. V=0, internal impedance of ideal voltage source is ZERO (short circuit)).
Replacing all other independent current sources with an open circuit (thereby eliminating current. i.e. I=0, internal impedance of ideal current source is infinite (open circuit).
we gotta follow the same procedure for any other voltage and current sources turn by turn...

Answer 6

after you have done that. You will find answers for all the others voltages and currents but How do you find the final answer?

Answer 7

just calculated using kvl and kcl and yes if you want to compare the two equivalent circuits try comparing with resistor across which you are calculating voltage just compare you found from thevinin's theorem ad from kvl..then if both are same then u have drawn correct thevinin's equivalent to that circuit..

Answer 8

ohkay. Thanks @shivaniits . It was really helpful

Answer 9

glad to know it helped!!