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

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?

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#### sandy.bridge

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 :)

#### sandy.bridge

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.

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