📌 Quick Answer
Thevenin’s theorem states that any linear, two-terminal electrical network can be replaced, as seen from those two terminals, by an equivalent circuit of a single voltage source (Vth) in series with a single resistance (Rth).
It greatly simplifies analysing how a network behaves when different loads are connected to it.
🔹 Key Takeaways
- Any linear two-terminal network = one voltage source Vth in series with one resistance Rth.
- Vth is the open-circuit voltage at the two terminals.
- Rth is the resistance seen from the terminals with all independent sources turned off.
- It is ideal for finding the current in one load resistor that may be changed.
Statement of Thevenin’s Theorem
Thevenin’s theorem states that any linear, bilateral, two-terminal network of voltage sources, current sources and resistances can be replaced by an equivalent circuit consisting of a single voltage source Vth in series with a single resistance Rth, connected across the two terminals.
Steps to Find the Thevenin Equivalent
- Remove the load resistor from the two terminals of interest.
- Find Vth, the open-circuit voltage across those two terminals.
- Find Rth by turning off all independent sources (short voltage sources, open current sources) and computing the resistance looking back into the terminals.
- Draw the equivalent circuit: Vth in series with Rth, then reconnect the load and find the load current as I = Vth / (Rth + R_load).
Applications
Thevenin’s theorem is most useful when the current or voltage in one particular element (the load) must be found for several different load values, because the rest of the network is reduced once to a simple source and resistance. It is widely used in circuit analysis, power systems and electronics design.
Frequently Asked Questions
What is Thevenin’s theorem?
It states that any linear two-terminal network can be replaced by a single voltage source Vth in series with a resistance Rth, as seen from those terminals.
How do you find the Thevenin voltage?
Vth is the open-circuit voltage measured across the two terminals after removing the load.
How do you find the Thevenin resistance?
Turn off all independent sources (short-circuit voltage sources and open-circuit current sources) and find the resistance looking back into the two terminals.
What is the difference between Thevenin’s and Norton’s theorems?
Thevenin’s gives a voltage source in series with a resistance, while Norton’s gives a current source in parallel with the same resistance; the two equivalents are interchangeable.
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