Generally, we use Kirchoff’s and Ohm’s laws to analyse and solve complicated electric circuits. Besides these laws, there are numerous circuit analysis methods that can be used to calculate the voltage and current at any given junction in a circuit. Thevenin’s Theorem is one of the most frequently used circuit theorems.
Definition of Thevenin’s Theorem
Fundamentally, Thevenin’s Theorem shows that it is possible to simplify any linear electric circuit to an equivalent electric circuit with one voltage source and series resistance, no matter how complicated the circuit is.
A Thevenin equivalent circuit is depicted in the diagram. Here, multiple resistive circuit components are substituted by a single equivalent resistance Rs and numerous energy outputs by an equivalent voltage source Vs.
Important Thevenin’s Theorem Questions with Answers
1) State Thevenin’s Theorem.
Thevenin’s Theorem shows that it is possible to simplify any linear electric circuit to an equivalent electric circuit with one voltage source and series resistance, no matter how complicated the circuit is.
2) What is Thevenin Voltage?
It is the open-circuit voltage that is present over the given two terminals.
3) What is the application of Thevenin’s Theorem?
Circuit analysis of power systems is done using Thevenin’s Theorem.
4) Can Thevenin’s Theorem be applied to a non-linear circuit?
No, applying Thevenin’s Theorem to a non-linear circuit is not possible.
5) Can Thevenin’s Theorem be applied to AC circuits?
Yes, Thevenin’s Theorem can be applied to AC circuits with linear elements like inductors, capacitors, and resistors.
6) What are the theoretical limitations of Thevenin’s Theorem?
Thevenin’s Theorem can only be used in linear circuits analysis. Thevenin’s Theorem is not applicable in electrical circuits with magnetic coupling among the load, and any other circuit component.
7) What are the steps to follow Thevenin’s Theorem?
The main steps are:
- Find the voltage of the Thevenin source by detaching the load resistor from the given circuit, and measuring the voltage over the open connection junctions where the load resistor is connected.
- Calculate the Thevenin resistance by detaching all the power sources in the original electrical circuit (current sources open and voltage sources shorted), and measuring the total resistance across the open connection points.
- Draw the derived Thevenin circuit, with the Thevenin resistance in series with the Thevenin voltage source.
- Analyse current and voltage for the load resistor following the laws of series electrical circuits.
8) Who derived Thevenin’s Theorem?
Thevenin’s Theorem was independently developed in 1853 by Hermann von Helmholtz and in 1884 by Léon Charles Thévenin.
9) Is it possible to simplify any complex linear circuits?
Yes, by using Thevenin’s Theorem, it is possible to simplify any linear electric circuit, no matter how complicated the circuit is, to an equivalent electric circuit with one voltage source and series resistance.
10) Give a few examples of network analysis theorems.
Thevenin’s Theorem, Superposition Theorem, Maximum Power Transfer Theorem, Norton’s Theorem, etc., are a few examples of network analysis theorems.
11) Thevenin’s Theorem and ____________ are extensively used to make electrical circuit analysis simpler. They are also used to study the initial-condition of a circuit and steady-state response.
Answer: Norton’s Theorem
Explanation: Thevenin’s Theorem and Norton’s Theorem are extensively used to make electrical circuit analysis simpler. They are also used to study the initial-condition of a circuit and steady-state response.
12) What is a steady-state response?
A steady-state response is the nature of an electrical circuit after an extended time when steady states have been attained after an external excitation.
13) Compare Thevenin’s Theorem and Norton’s Theorem.
- Thevenin’s Theorem utilises a voltage source, while Norton’s Theorem uses a current source.
- Norton’s Theorem employs a resistor set in parallel over the source, whereas Thevenin’s Theorem utilises a resistor in series.
- From Thevenin’s Theorem, Norton’s Theorem can be easily derived.
- Thevenin’s resistance and Norton’s resistance are equal in value.
- Thevenin’s equivalent circuit and Norton’s equivalent circuit can be straightforwardly interchanged.
14) What are the practical limitations of Thevenin’s Theorem?
The practical limitations of Thevenin’s Theorem:
- Many electrical circuits are only linear within a certain range of values. Therefore, Thevenin’s Theorem is only valid along this linear range.
- The Thevenin’s equivalent has equivalent I-V characteristics only from the load’s point of view.
- The Thevenin equivalent’s power dissipation is not strictly identical to the real system’s power dissipation. But power dissipated by an external resistor among two output terminals is identical, despite how the internal resistance is.
Practice Questions
1) What are the examples of Thevenin’s Theorem?
2) What are the important applications of Thevenin’s Theorem?
3) What is the difference between Thevenin’s Theorem and Norton’s Theorem
4) What is a Thevenin resistance?
5) What is a Thevenin Voltage?
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