# Thevenin's Theorem : Reason behind 'nullifying' or 'suppressing' sources?

In summary, according to Thevenin's theorem, when trying to nullify the effect of all sources, voltage sources must be short circuited and current sources must be open circuited. This is because an inactive voltage source is equivalent to a short circuit, while an inactive current source is equivalent to an open circuit. Replacing the voltage source with an open circuit or the current source with a short circuit would not accurately nullify their effects.

WHY aren't voltage sources open circuited and current sources short circuited?

Thevenin's theorem (and even Superposition Theorem) states that we need to 'suppress' or 'nullify' the effect of all sources. We do this by short circuiting voltage sources and open circuiting current sources. WHY exactly can't we do this the other way round by open circuiting voltage sources and short circuiting current sources? What is wrong about doing that?

An inactive voltage source is equivalent to zero volts between its terminals, independent of the current through it. This would be a "wire", or a short circuit.

An inactive current source is a current source in which no current can flow independent of the voltage across, which is represented by infinite impedance, and hence an open circuit.

Thanks a lot! You are awesome :)

If you were to replace the voltage source with an open circuit rather than a short circuit, there may exist a voltage difference across its terminals (dependent on the rest of the network) and hence it would not be considered an "inactive" voltage source. Similar arguments would apply to the current source.

## 1) What is Thevenin's Theorem?

Thevenin's Theorem is a fundamental concept in electrical engineering that states that any linear, two-terminal network can be replaced by an equivalent circuit containing a single voltage source and a single series resistor. This simplifies complex circuits and allows for easier analysis and design.

## 2) Why do we nullify or suppress sources in Thevenin's Theorem?

The process of nullifying or suppressing sources in Thevenin's Theorem is done to simplify the circuit and make it easier to analyze. By replacing the original sources with an equivalent voltage source, the circuit becomes more manageable and can be solved using basic circuit analysis techniques.

## 3) What is the reason behind using a single resistor in Thevenin's Theorem?

The single resistor in Thevenin's Theorem represents the internal resistance of the original circuit. It is used to account for the voltage drop that occurs within the original circuit and is necessary for the equivalent circuit to accurately represent the behavior of the original circuit.

## 4) Is Thevenin's Theorem only applicable to DC circuits?

No, Thevenin's Theorem is applicable to both DC and AC circuits as long as they are linear and two-terminal. However, the calculations for determining the equivalent circuit may differ for AC circuits due to the presence of reactance.

## 5) How is Thevenin's Theorem useful in practical applications?

Thevenin's Theorem is useful in practical applications because it allows for the simplification of complex circuits, making it easier to analyze and design. This helps engineers and scientists to better understand and predict the behavior of a circuit, leading to more efficient and reliable designs.